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| author | alk3pInjection <webmaster@raspii.tech> | 2024-02-04 16:16:35 +0800 |
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| committer | alk3pInjection <webmaster@raspii.tech> | 2024-02-04 16:16:35 +0800 |
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diff --git a/share/doc/gfortran/Code-Gen-Options.html b/share/doc/gfortran/Code-Gen-Options.html new file mode 100644 index 0000000..659806d --- /dev/null +++ b/share/doc/gfortran/Code-Gen-Options.html @@ -0,0 +1,680 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<!-- Copyright (C) 1999-2023 Free Software Foundation, Inc. + +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.3 or +any later version published by the Free Software Foundation; with the +Invariant Sections being "Funding Free Software", the Front-Cover +Texts being (a) (see below), and with the Back-Cover Texts being (b) +(see below). A copy of the license is included in the section entitled +"GNU Free Documentation License". + +(a) The FSF's Front-Cover Text is: + +A GNU Manual + +(b) The FSF's Back-Cover Text is: + +You have freedom to copy and modify this GNU Manual, like GNU + software. Copies published by the Free Software Foundation raise + funds for GNU development. --> +<!-- Created by GNU Texinfo 5.1, http://www.gnu.org/software/texinfo/ --> +<head> +<title>The GNU Fortran Compiler: Code Gen Options</title> + +<meta name="description" content="The GNU Fortran Compiler: Code Gen Options"> +<meta name="keywords" content="The GNU Fortran Compiler: Code Gen Options"> +<meta name="resource-type" content="document"> +<meta name="distribution" content="global"> +<meta name="Generator" content="makeinfo"> +<meta http-equiv="Content-Type" content="text/html; charset=utf-8"> +<link href="index.html#Top" rel="start" title="Top"> +<link href="Option-Index.html#Option-Index" rel="index" title="Option Index"> +<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> +<link href="Invoking-GNU-Fortran.html#Invoking-GNU-Fortran" rel="up" title="Invoking GNU Fortran"> +<link href="Interoperability-Options.html#Interoperability-Options" rel="next" title="Interoperability Options"> +<link href="Runtime-Options.html#Runtime-Options" rel="previous" title="Runtime Options"> +<style type="text/css"> +<!-- +a.summary-letter {text-decoration: none} +blockquote.smallquotation {font-size: smaller} +div.display {margin-left: 3.2em} +div.example {margin-left: 3.2em} +div.indentedblock {margin-left: 3.2em} +div.lisp {margin-left: 3.2em} +div.smalldisplay {margin-left: 3.2em} +div.smallexample {margin-left: 3.2em} +div.smallindentedblock {margin-left: 3.2em; font-size: smaller} +div.smalllisp {margin-left: 3.2em} +kbd {font-style:oblique} +pre.display {font-family: inherit} +pre.format {font-family: inherit} +pre.menu-comment {font-family: serif} +pre.menu-preformatted {font-family: serif} +pre.smalldisplay {font-family: inherit; font-size: smaller} +pre.smallexample {font-size: smaller} +pre.smallformat {font-family: inherit; font-size: smaller} +pre.smalllisp {font-size: smaller} +span.nocodebreak {white-space:nowrap} +span.nolinebreak {white-space:nowrap} +span.roman {font-family:serif; font-weight:normal} +span.sansserif {font-family:sans-serif; font-weight:normal} +ul.no-bullet {list-style: none} +--> +</style> + + +</head> + +<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> +<a name="Code-Gen-Options"></a> +<div class="header"> +<p> +Next: <a href="Interoperability-Options.html#Interoperability-Options" accesskey="n" rel="next">Interoperability Options</a>, Previous: <a href="Runtime-Options.html#Runtime-Options" accesskey="p" rel="previous">Runtime Options</a>, Up: <a href="Invoking-GNU-Fortran.html#Invoking-GNU-Fortran" accesskey="u" rel="up">Invoking GNU Fortran</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p> +</div> +<hr> +<a name="Options-for-code-generation-conventions"></a> +<h3 class="section">2.9 Options for code generation conventions</h3> +<a name="index-code-generation_002c-conventions"></a> +<a name="index-options_002c-code-generation"></a> +<a name="index-options_002c-run_002dtime"></a> + +<p>These machine-independent options control the interface conventions +used in code generation. +</p> +<p>Most of them have both positive and negative forms; the negative form +of <samp>-ffoo</samp> would be <samp>-fno-foo</samp>. In the table below, only +one of the forms is listed—the one which is not the default. You +can figure out the other form by either removing <samp>no-</samp> or adding +it. +</p> +<dl compact="compact"> +<dd><a name="index-fno_002dautomatic"></a> +<a name="index-SAVE-statement"></a> +<a name="index-statement_002c-SAVE"></a> +</dd> +<dt><code>-fno-automatic</code></dt> +<dd><p>Treat each program unit (except those marked as RECURSIVE) as if the +<code>SAVE</code> statement were specified for every local variable and array +referenced in it. Does not affect common blocks. (Some Fortran compilers +provide this option under the name <samp>-static</samp> or <samp>-save</samp>.) +The default, which is <samp>-fautomatic</samp>, uses the stack for local +variables smaller than the value given by <samp>-fmax-stack-var-size</samp>. +Use the option <samp>-frecursive</samp> to use no static memory. +</p> +<p>Local variables or arrays having an explicit <code>SAVE</code> attribute are +silently ignored unless the <samp>-pedantic</samp> option is added. +</p> +<a name="index-ff2c"></a> +<a name="index-calling-convention"></a> +<a name="index-f2c-calling-convention"></a> +<a name="index-g77-calling-convention"></a> +<a name="index-libf2c-calling-convention"></a> +</dd> +<dt><code>-ff2c</code></dt> +<dd><p>Generate code designed to be compatible with code generated +by <code>g77</code> and <code>f2c</code>. +</p> +<p>The calling conventions used by <code>g77</code> (originally implemented +in <code>f2c</code>) require functions that return type +default <code>REAL</code> to actually return the C type <code>double</code>, and +functions that return type <code>COMPLEX</code> to return the values via an +extra argument in the calling sequence that points to where to +store the return value. Under the default GNU calling conventions, such +functions simply return their results as they would in GNU +C—default <code>REAL</code> functions return the C type <code>float</code>, and +<code>COMPLEX</code> functions return the GNU C type <code>complex</code>. +Additionally, this option implies the <samp>-fsecond-underscore</samp> +option, unless <samp>-fno-second-underscore</samp> is explicitly requested. +</p> +<p>This does not affect the generation of code that interfaces with +the <code>libgfortran</code> library. +</p> +<p><em>Caution:</em> It is not a good idea to mix Fortran code compiled with +<samp>-ff2c</samp> with code compiled with the default <samp>-fno-f2c</samp> +calling conventions as, calling <code>COMPLEX</code> or default <code>REAL</code> +functions between program parts which were compiled with different +calling conventions will break at execution time. +</p> +<p><em>Caution:</em> This will break code which passes intrinsic functions +of type default <code>REAL</code> or <code>COMPLEX</code> as actual arguments, as +the library implementations use the <samp>-fno-f2c</samp> calling conventions. +</p> +<a name="index-fno_002dunderscoring"></a> +<a name="index-underscore"></a> +<a name="index-symbol-names_002c-underscores"></a> +<a name="index-transforming-symbol-names"></a> +<a name="index-symbol-names_002c-transforming"></a> +</dd> +<dt><code>-fno-underscoring</code></dt> +<dd><p>Do not transform names of entities specified in the Fortran +source file by appending underscores to them. +</p> +<p>With <samp>-funderscoring</samp> in effect, GNU Fortran appends one +underscore to external names. This is done to ensure +compatibility with code produced by many UNIX Fortran compilers. +</p> +<p><em>Caution</em>: The default behavior of GNU Fortran is +incompatible with <code>f2c</code> and <code>g77</code>, please use the +<samp>-ff2c</samp> option if you want object files compiled with +GNU Fortran to be compatible with object code created with these +tools. +</p> +<p>Use of <samp>-fno-underscoring</samp> is not recommended unless you are +experimenting with issues such as integration of GNU Fortran into +existing system environments (vis-à-vis existing libraries, tools, +and so on). +</p> +<p>For example, with <samp>-funderscoring</samp>, and assuming that <code>j()</code> and +<code>max_count()</code> are external functions while <code>my_var</code> and +<code>lvar</code> are local variables, a statement like +</p><div class="smallexample"> +<pre class="smallexample">I = J() + MAX_COUNT (MY_VAR, LVAR) +</pre></div> +<p>is implemented as something akin to: +</p><div class="smallexample"> +<pre class="smallexample">i = j_() + max_count_(&my_var, &lvar); +</pre></div> + +<p>With <samp>-fno-underscoring</samp>, the same statement is implemented as: +</p> +<div class="smallexample"> +<pre class="smallexample">i = j() + max_count(&my_var, &lvar); +</pre></div> + +<p>Use of <samp>-fno-underscoring</samp> allows direct specification of +user-defined names while debugging and when interfacing GNU Fortran +code with other languages. +</p> +<p>Note that just because the names match does <em>not</em> mean that the +interface implemented by GNU Fortran for an external name matches the +interface implemented by some other language for that same name. +That is, getting code produced by GNU Fortran to link to code produced +by some other compiler using this or any other method can be only a +small part of the overall solution—getting the code generated by +both compilers to agree on issues other than naming can require +significant effort, and, unlike naming disagreements, linkers normally +cannot detect disagreements in these other areas. +</p> +<p>Also, note that with <samp>-fno-underscoring</samp>, the lack of appended +underscores introduces the very real possibility that a user-defined +external name will conflict with a name in a system library, which +could make finding unresolved-reference bugs quite difficult in some +cases—they might occur at program run time, and show up only as +buggy behavior at run time. +</p> +<p>In future versions of GNU Fortran we hope to improve naming and linking +issues so that debugging always involves using the names as they appear +in the source, even if the names as seen by the linker are mangled to +prevent accidental linking between procedures with incompatible +interfaces. +</p> +<a name="index-fsecond_002dunderscore"></a> +<a name="index-underscore-1"></a> +<a name="index-symbol-names_002c-underscores-1"></a> +<a name="index-transforming-symbol-names-1"></a> +<a name="index-symbol-names_002c-transforming-1"></a> +<a name="index-f2c-calling-convention-1"></a> +<a name="index-g77-calling-convention-1"></a> +<a name="index-libf2c-calling-convention-1"></a> +</dd> +<dt><code>-fsecond-underscore</code></dt> +<dd><p>By default, GNU Fortran appends an underscore to external +names. If this option is used GNU Fortran appends two +underscores to names with underscores and one underscore to external names +with no underscores. GNU Fortran also appends two underscores to +internal names with underscores to avoid naming collisions with external +names. +</p> +<p>This option has no effect if <samp>-fno-underscoring</samp> is +in effect. It is implied by the <samp>-ff2c</samp> option. +</p> +<p>Otherwise, with this option, an external name such as <code>MAX_COUNT</code> +is implemented as a reference to the link-time external symbol +<code>max_count__</code>, instead of <code>max_count_</code>. This is required +for compatibility with <code>g77</code> and <code>f2c</code>, and is implied +by use of the <samp>-ff2c</samp> option. +</p> +<a name="index-fcoarray"></a> +<a name="index-coarrays"></a> +</dd> +<dt><code>-fcoarray=<var><keyword></var></code></dt> +<dd> +<dl compact="compact"> +<dt>‘<samp>none</samp>’</dt> +<dd><p>Disable coarray support; using coarray declarations and image-control +statements will produce a compile-time error. (Default) +</p> +</dd> +<dt>‘<samp>single</samp>’</dt> +<dd><p>Single-image mode, i.e. <code>num_images()</code> is always one. +</p> +</dd> +<dt>‘<samp>lib</samp>’</dt> +<dd><p>Library-based coarray parallelization; a suitable GNU Fortran coarray +library needs to be linked. +</p></dd> +</dl> + + +<a name="index-fcheck"></a> +<a name="index-array_002c-bounds-checking"></a> +<a name="index-bit-intrinsics-checking"></a> +<a name="index-bounds-checking"></a> +<a name="index-pointer-checking"></a> +<a name="index-memory-checking"></a> +<a name="index-range-checking"></a> +<a name="index-subscript-checking"></a> +<a name="index-checking-subscripts"></a> +<a name="index-run_002dtime-checking"></a> +<a name="index-checking-array-temporaries"></a> +</dd> +<dt><code>-fcheck=<var><keyword></var></code></dt> +<dd> +<p>Enable the generation of run-time checks; the argument shall be +a comma-delimited list of the following keywords. Prefixing a check with +<samp>no-</samp> disables it if it was activated by a previous specification. +</p> +<dl compact="compact"> +<dt>‘<samp>all</samp>’</dt> +<dd><p>Enable all run-time test of <samp>-fcheck</samp>. +</p> +</dd> +<dt>‘<samp>array-temps</samp>’</dt> +<dd><p>Warns at run time when for passing an actual argument a temporary array +had to be generated. The information generated by this warning is +sometimes useful in optimization, in order to avoid such temporaries. +</p> +<p>Note: The warning is only printed once per location. +</p> +</dd> +<dt>‘<samp>bits</samp>’</dt> +<dd><p>Enable generation of run-time checks for invalid arguments to the bit +manipulation intrinsics. +</p> +</dd> +<dt>‘<samp>bounds</samp>’</dt> +<dd><p>Enable generation of run-time checks for array subscripts +and against the declared minimum and maximum values. It also +checks array indices for assumed and deferred +shape arrays against the actual allocated bounds and ensures that all string +lengths are equal for character array constructors without an explicit +typespec. +</p> +<p>Some checks require that <samp>-fcheck=bounds</samp> is set for +the compilation of the main program. +</p> +<p>Note: In the future this may also include other forms of checking, e.g., +checking substring references. +</p> +</dd> +<dt>‘<samp>do</samp>’</dt> +<dd><p>Enable generation of run-time checks for invalid modification of loop +iteration variables. +</p> +</dd> +<dt>‘<samp>mem</samp>’</dt> +<dd><p>Enable generation of run-time checks for memory allocation. +Note: This option does not affect explicit allocations using the +<code>ALLOCATE</code> statement, which will be always checked. +</p> +</dd> +<dt>‘<samp>pointer</samp>’</dt> +<dd><p>Enable generation of run-time checks for pointers and allocatables. +</p> +</dd> +<dt>‘<samp>recursion</samp>’</dt> +<dd><p>Enable generation of run-time checks for recursively called subroutines and +functions which are not marked as recursive. See also <samp>-frecursive</samp>. +Note: This check does not work for OpenMP programs and is disabled if used +together with <samp>-frecursive</samp> and <samp>-fopenmp</samp>. +</p></dd> +</dl> + +<p>Example: Assuming you have a file <samp>foo.f90</samp>, the command +</p><div class="smallexample"> +<pre class="smallexample"> gfortran -fcheck=all,no-array-temps foo.f90 +</pre></div> +<p>will compile the file with all checks enabled as specified above except +warnings for generated array temporaries. +</p> + +<a name="index-fbounds_002dcheck"></a> +</dd> +<dt><code>-fbounds-check</code></dt> +<dd><p>Deprecated alias for <samp>-fcheck=bounds</samp>. +</p> +<a name="index-tail_002dcall_002dworkaround"></a> +</dd> +<dt><code>-ftail-call-workaround</code></dt> +<dt><code>-ftail-call-workaround=<var>n</var></code></dt> +<dd><p>Some C interfaces to Fortran codes violate the gfortran ABI by +omitting the hidden character length arguments as described in +See <a href="Argument-passing-conventions.html#Argument-passing-conventions">Argument passing conventions</a>. This can lead to crashes +because pushing arguments for tail calls can overflow the stack. +</p> +<p>To provide a workaround for existing binary packages, this option +disables tail call optimization for gfortran procedures with character +arguments. With <samp>-ftail-call-workaround=2</samp> tail call optimization +is disabled in all gfortran procedures with character arguments, +with <samp>-ftail-call-workaround=1</samp> or equivalent +<samp>-ftail-call-workaround</samp> only in gfortran procedures with character +arguments that call implicitly prototyped procedures. +</p> +<p>Using this option can lead to problems including crashes due to +insufficient stack space. +</p> +<p>It is <em>very strongly</em> recommended to fix the code in question. +The <samp>-fc-prototypes-external</samp> option can be used to generate +prototypes which conform to gfortran’s ABI, for inclusion in the +source code. +</p> +<p>Support for this option will likely be withdrawn in a future release +of gfortran. +</p> +<p>The negative form, <samp>-fno-tail-call-workaround</samp> or equivalent +<samp>-ftail-call-workaround=0</samp>, can be used to disable this option. +</p> +<p>Default is currently <samp>-ftail-call-workaround</samp>, this will change +in future releases. +</p> +<a name="index-fcheck_002darray_002dtemporaries"></a> +</dd> +<dt><code>-fcheck-array-temporaries</code></dt> +<dd><p>Deprecated alias for <samp>-fcheck=array-temps</samp>. +</p> +<a name="index-fmax_002darray_002dconstructor"></a> +</dd> +<dt><code>-fmax-array-constructor=<var>n</var></code></dt> +<dd><p>This option can be used to increase the upper limit permitted in +array constructors. The code below requires this option to expand +the array at compile time. +</p> +<div class="smallexample"> +<pre class="smallexample">program test +implicit none +integer j +integer, parameter :: n = 100000 +integer, parameter :: i(n) = (/ (2*j, j = 1, n) /) +print '(10(I0,1X))', i +end program test +</pre></div> + +<p><em>Caution: This option can lead to long compile times and excessively +large object files.</em> +</p> +<p>The default value for <var>n</var> is 65535. +</p> + +<a name="index-fmax_002dstack_002dvar_002dsize"></a> +</dd> +<dt><code>-fmax-stack-var-size=<var>n</var></code></dt> +<dd><p>This option specifies the size in bytes of the largest array that will be put +on the stack; if the size is exceeded static memory is used (except in +procedures marked as RECURSIVE). Use the option <samp>-frecursive</samp> to +allow for recursive procedures which do not have a RECURSIVE attribute or +for parallel programs. Use <samp>-fno-automatic</samp> to never use the stack. +</p> +<p>This option currently only affects local arrays declared with constant +bounds, and may not apply to all character variables. +Future versions of GNU Fortran may improve this behavior. +</p> +<p>The default value for <var>n</var> is 65536. +</p> +<a name="index-fstack_002darrays"></a> +</dd> +<dt><code>-fstack-arrays</code></dt> +<dd><p>Adding this option will make the Fortran compiler put all arrays of +unknown size and array temporaries onto stack memory. If your program uses very +large local arrays it is possible that you will have to extend your runtime +limits for stack memory on some operating systems. This flag is enabled +by default at optimization level <samp>-Ofast</samp> unless +<samp>-fmax-stack-var-size</samp> is specified. +</p> +<a name="index-fpack_002dderived"></a> +<a name="index-structure-packing"></a> +</dd> +<dt><code>-fpack-derived</code></dt> +<dd><p>This option tells GNU Fortran to pack derived type members as closely as +possible. Code compiled with this option is likely to be incompatible +with code compiled without this option, and may execute slower. +</p> +<a name="index-frepack_002darrays"></a> +<a name="index-repacking-arrays"></a> +</dd> +<dt><code>-frepack-arrays</code></dt> +<dd><p>In some circumstances GNU Fortran may pass assumed shape array +sections via a descriptor describing a noncontiguous area of memory. +This option adds code to the function prologue to repack the data into +a contiguous block at runtime. +</p> +<p>This should result in faster accesses to the array. However it can introduce +significant overhead to the function call, especially when the passed data +is noncontiguous. +</p> +<a name="index-fshort_002denums"></a> +</dd> +<dt><code>-fshort-enums</code></dt> +<dd><p>This option is provided for interoperability with C code that was +compiled with the <samp>-fshort-enums</samp> option. It will make +GNU Fortran choose the smallest <code>INTEGER</code> kind a given +enumerator set will fit in, and give all its enumerators this kind. +</p> +<a name="index-finline_002darg_002dpacking"></a> +</dd> +<dt><code>-finline-arg-packing</code></dt> +<dd><p>When passing an assumed-shape argument of a procedure as actual +argument to an assumed-size or explicit size or as argument to a +procedure that does not have an explicit interface, the argument may +have to be packed, that is put into contiguous memory. An example is +the call to <code>foo</code> in +</p><div class="smallexample"> +<pre class="smallexample"> subroutine foo(a) + real, dimension(*) :: a + end subroutine foo + subroutine bar(b) + real, dimension(:) :: b + call foo(b) + end subroutine bar +</pre></div> + +<p>When <samp>-finline-arg-packing</samp> is in effect, this packing will be +performed by inline code. This allows for more optimization while +increasing code size. +</p> +<p><samp>-finline-arg-packing</samp> is implied by any of the <samp>-O</samp> options +except when optimizing for size via <samp>-Os</samp>. If the code +contains a very large number of argument that have to be packed, code +size and also compilation time may become excessive. If that is the +case, it may be better to disable this option. Instances of packing +can be found by using <samp>-Warray-temporaries</samp>. +</p> +<a name="index-fexternal_002dblas"></a> +</dd> +<dt><code>-fexternal-blas</code></dt> +<dd><p>This option will make <code>gfortran</code> generate calls to BLAS functions +for some matrix operations like <code>MATMUL</code>, instead of using our own +algorithms, if the size of the matrices involved is larger than a given +limit (see <samp>-fblas-matmul-limit</samp>). This may be profitable if an +optimized vendor BLAS library is available. The BLAS library will have +to be specified at link time. +</p> +<a name="index-fblas_002dmatmul_002dlimit"></a> +</dd> +<dt><code>-fblas-matmul-limit=<var>n</var></code></dt> +<dd><p>Only significant when <samp>-fexternal-blas</samp> is in effect. +Matrix multiplication of matrices with size larger than (or equal to) <var>n</var> +will be performed by calls to BLAS functions, while others will be +handled by <code>gfortran</code> internal algorithms. If the matrices +involved are not square, the size comparison is performed using the +geometric mean of the dimensions of the argument and result matrices. +</p> +<p>The default value for <var>n</var> is 30. +</p> +<a name="index-finline_002dmatmul_002dlimit"></a> +</dd> +<dt><code>-finline-matmul-limit=<var>n</var></code></dt> +<dd><p>When front-end optimization is active, some calls to the <code>MATMUL</code> +intrinsic function will be inlined. This may result in code size +increase if the size of the matrix cannot be determined at compile +time, as code for both cases is generated. Setting +<code>-finline-matmul-limit=0</code> will disable inlining in all cases. +Setting this option with a value of <var>n</var> will produce inline code +for matrices with size up to <var>n</var>. If the matrices involved are not +square, the size comparison is performed using the geometric mean of +the dimensions of the argument and result matrices. +</p> +<p>The default value for <var>n</var> is 30. The <code>-fblas-matmul-limit</code> +can be used to change this value. +</p> +<a name="index-frecursive"></a> +</dd> +<dt><code>-frecursive</code></dt> +<dd><p>Allow indirect recursion by forcing all local arrays to be allocated +on the stack. This flag cannot be used together with +<samp>-fmax-stack-var-size=</samp> or <samp>-fno-automatic</samp>. +</p> +<a name="index-finit_002dlocal_002dzero"></a> +<a name="index-finit_002dderived"></a> +<a name="index-finit_002dinteger"></a> +<a name="index-finit_002dreal"></a> +<a name="index-finit_002dlogical"></a> +<a name="index-finit_002dcharacter"></a> +</dd> +<dt><code>-finit-local-zero</code></dt> +<dt><code>-finit-derived</code></dt> +<dt><code>-finit-integer=<var>n</var></code></dt> +<dt><code>-finit-real=<var><zero|inf|-inf|nan|snan></var></code></dt> +<dt><code>-finit-logical=<var><true|false></var></code></dt> +<dt><code>-finit-character=<var>n</var></code></dt> +<dd><p>The <samp>-finit-local-zero</samp> option instructs the compiler to +initialize local <code>INTEGER</code>, <code>REAL</code>, and <code>COMPLEX</code> +variables to zero, <code>LOGICAL</code> variables to false, and +<code>CHARACTER</code> variables to a string of null bytes. Finer-grained +initialization options are provided by the +<samp>-finit-integer=<var>n</var></samp>, +<samp>-finit-real=<var><zero|inf|-inf|nan|snan></var></samp> (which also initializes +the real and imaginary parts of local <code>COMPLEX</code> variables), +<samp>-finit-logical=<var><true|false></var></samp>, and +<samp>-finit-character=<var>n</var></samp> (where <var>n</var> is an ASCII character +value) options. +</p> +<p>With <samp>-finit-derived</samp>, components of derived type variables will be +initialized according to these flags. Components whose type is not covered by +an explicit <samp>-finit-*</samp> flag will be treated as described above with +<samp>-finit-local-zero</samp>. +</p> +<p>These options do not initialize +</p><ul> +<li> objects with the POINTER attribute +</li><li> allocatable arrays +</li><li> variables that appear in an <code>EQUIVALENCE</code> statement. +</li></ul> +<p>(These limitations may be removed in future releases). +</p> +<p>Note that the <samp>-finit-real=nan</samp> option initializes <code>REAL</code> +and <code>COMPLEX</code> variables with a quiet NaN. For a signalling NaN +use <samp>-finit-real=snan</samp>; note, however, that compile-time +optimizations may convert them into quiet NaN and that trapping +needs to be enabled (e.g. via <samp>-ffpe-trap</samp>). +</p> +<p>The <samp>-finit-integer</samp> option will parse the value into an +integer of type <code>INTEGER(kind=C_LONG)</code> on the host. Said value +is then assigned to the integer variables in the Fortran code, which +might result in wraparound if the value is too large for the kind. +</p> +<p>Finally, note that enabling any of the <samp>-finit-*</samp> options will +silence warnings that would have been emitted by <samp>-Wuninitialized</samp> +for the affected local variables. +</p> +<a name="index-falign_002dcommons"></a> +<a name="index-alignment-of-COMMON-blocks-1"></a> +</dd> +<dt><code>-falign-commons</code></dt> +<dd><p>By default, <code>gfortran</code> enforces proper alignment of all variables in a +<code>COMMON</code> block by padding them as needed. On certain platforms this is mandatory, +on others it increases performance. If a <code>COMMON</code> block is not declared with +consistent data types everywhere, this padding can cause trouble, and +<samp>-fno-align-commons</samp> can be used to disable automatic alignment. The +same form of this option should be used for all files that share a <code>COMMON</code> block. +To avoid potential alignment issues in <code>COMMON</code> blocks, it is recommended to order +objects from largest to smallest. +</p> +<a name="index-fno_002dprotect_002dparens"></a> +<a name="index-re_002dassociation-of-parenthesized-expressions"></a> +</dd> +<dt><code>-fno-protect-parens</code></dt> +<dd><p>By default the parentheses in expression are honored for all optimization +levels such that the compiler does not do any re-association. Using +<samp>-fno-protect-parens</samp> allows the compiler to reorder <code>REAL</code> and +<code>COMPLEX</code> expressions to produce faster code. Note that for the re-association +optimization <samp>-fno-signed-zeros</samp> and <samp>-fno-trapping-math</samp> +need to be in effect. The parentheses protection is enabled by default, unless +<samp>-Ofast</samp> is given. +</p> +<a name="index-frealloc_002dlhs"></a> +<a name="index-Reallocate-the-LHS-in-assignments"></a> +</dd> +<dt><code>-frealloc-lhs</code></dt> +<dd><p>An allocatable left-hand side of an intrinsic assignment is automatically +(re)allocated if it is either unallocated or has a different shape. The +option is enabled by default except when <samp>-std=f95</samp> is given. See +also <samp>-Wrealloc-lhs</samp>. +</p> +<a name="index-faggressive_002dfunction_002delimination"></a> +<a name="index-Elimination-of-functions-with-identical-argument-lists"></a> +</dd> +<dt><code>-faggressive-function-elimination</code></dt> +<dd><p>Functions with identical argument lists are eliminated within +statements, regardless of whether these functions are marked +<code>PURE</code> or not. For example, in +</p><div class="smallexample"> +<pre class="smallexample"> a = f(b,c) + f(b,c) +</pre></div> +<p>there will only be a single call to <code>f</code>. This option only works +if <samp>-ffrontend-optimize</samp> is in effect. +</p> +<a name="index-frontend_002doptimize"></a> +<a name="index-Front_002dend-optimization"></a> +</dd> +<dt><code>-ffrontend-optimize</code></dt> +<dd><p>This option performs front-end optimization, based on manipulating +parts the Fortran parse tree. Enabled by default by any <samp>-O</samp> option +except <samp>-O0</samp> and <samp>-Og</samp>. Optimizations enabled by this option +include: +</p><ul> +<li> inlining calls to <code>MATMUL</code>, +</li><li> elimination of identical function calls within expressions, +</li><li> removing unnecessary calls to <code>TRIM</code> in comparisons and assignments, +</li><li> replacing <code>TRIM(a)</code> with <code>a(1:LEN_TRIM(a))</code> and +</li><li> short-circuiting of logical operators (<code>.AND.</code> and <code>.OR.</code>). +</li></ul> +<p>It can be deselected by specifying <samp>-fno-frontend-optimize</samp>. +</p> +<a name="index-frontend_002dloop_002dinterchange"></a> +<a name="index-loop-interchange_002c-Fortran"></a> +</dd> +<dt><code>-ffrontend-loop-interchange</code></dt> +<dd><p>Attempt to interchange loops in the Fortran front end where +profitable. Enabled by default by any <samp>-O</samp> option. +At the moment, this option only affects <code>FORALL</code> and +<code>DO CONCURRENT</code> statements with several forall triplets. +</p></dd> +</dl> + +<p>See <a href="http://gcc.gnu.org/onlinedocs/gcc/Code-Gen-Options.html#Code-Gen-Options">Options for Code Generation Conventions</a> in <cite>Using the GNU Compiler Collection (GCC)</cite>, for information on more options +offered by the GBE +shared by <code>gfortran</code>, <code>gcc</code>, and other GNU compilers. +</p> + +<hr> +<div class="header"> +<p> +Next: <a href="Interoperability-Options.html#Interoperability-Options" accesskey="n" rel="next">Interoperability Options</a>, Previous: <a href="Runtime-Options.html#Runtime-Options" accesskey="p" rel="previous">Runtime Options</a>, Up: <a href="Invoking-GNU-Fortran.html#Invoking-GNU-Fortran" accesskey="u" rel="up">Invoking GNU Fortran</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p> +</div> + + + +</body> +</html> |