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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 |
| commit | abdaadbcae30fe0c9a66c7516798279fdfd97750 (patch) | |
| tree | 00a54a6e25601e43876d03c1a4a12a749d4a914c /share/doc/gccint/Logical-Operators.html | |
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diff --git a/share/doc/gccint/Logical-Operators.html b/share/doc/gccint/Logical-Operators.html new file mode 100644 index 0000000..8e2bb5c --- /dev/null +++ b/share/doc/gccint/Logical-Operators.html @@ -0,0 +1,324 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<!-- Copyright (C) 1988-2023 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>GNU Compiler Collection (GCC) Internals: Logical Operators</title> + +<meta name="description" content="GNU Compiler Collection (GCC) Internals: Logical Operators"> +<meta name="keywords" content="GNU Compiler Collection (GCC) Internals: Logical Operators"> +<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="Operands.html#Operands" rel="up" title="Operands"> +<link href="Manipulating-GIMPLE-statements.html#Manipulating-GIMPLE-statements" rel="next" title="Manipulating GIMPLE statements"> +<link href="Conditional-Expressions.html#Conditional-Expressions" rel="previous" title="Conditional Expressions"> +<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="Logical-Operators"></a> +<div class="header"> +<p> +Previous: <a href="Conditional-Expressions.html#Conditional-Expressions" accesskey="p" rel="previous">Conditional Expressions</a>, Up: <a href="Operands.html#Operands" accesskey="u" rel="up">Operands</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="Logical-Operators-1"></a> +<h4 class="subsection">12.6.4 Logical Operators</h4> +<a name="index-Logical-Operators"></a> + +<p>Except when they appear in the condition operand of a +<code>GIMPLE_COND</code>, logical ‘and’ and ‘or’ operators are simplified +as follows: <code>a = b && c</code> becomes +</p> +<div class="smallexample"> +<pre class="smallexample">T1 = (bool)b; +if (T1 == true) + T1 = (bool)c; +a = T1; +</pre></div> + +<p>Note that <code>T1</code> in this example cannot be an expression temporary, +because it has two different assignments. +</p> +<a name="Manipulating-operands"></a> +<h4 class="subsection">12.6.5 Manipulating operands</h4> + +<p>All gimple operands are of type <code>tree</code>. But only certain +types of trees are allowed to be used as operand tuples. Basic +validation is controlled by the function +<code>get_gimple_rhs_class</code>, which given a tree code, returns an +<code>enum</code> with the following values of type <code>enum +gimple_rhs_class</code> +</p> +<ul> +<li> <code>GIMPLE_INVALID_RHS</code> +The tree cannot be used as a GIMPLE operand. + +</li><li> <code>GIMPLE_TERNARY_RHS</code> +The tree is a valid GIMPLE ternary operation. + +</li><li> <code>GIMPLE_BINARY_RHS</code> +The tree is a valid GIMPLE binary operation. + +</li><li> <code>GIMPLE_UNARY_RHS</code> +The tree is a valid GIMPLE unary operation. + +</li><li> <code>GIMPLE_SINGLE_RHS</code> +The tree is a single object, that cannot be split into simpler +operands (for instance, <code>SSA_NAME</code>, <code>VAR_DECL</code>, <code>COMPONENT_REF</code>, etc). + +<p>This operand class also acts as an escape hatch for tree nodes +that may be flattened out into the operand vector, but would need +more than two slots on the RHS. For instance, a <code>COND_EXPR</code> +expression of the form <code>(a op b) ? x : y</code> could be flattened +out on the operand vector using 4 slots, but it would also +require additional processing to distinguish <code>c = a op b</code> +from <code>c = a op b ? x : y</code>. In time, these special case tree +expressions should be flattened into the operand vector. +</p></li></ul> + +<p>For tree nodes in the categories <code>GIMPLE_TERNARY_RHS</code>, +<code>GIMPLE_BINARY_RHS</code> and <code>GIMPLE_UNARY_RHS</code>, they cannot be +stored inside tuples directly. They first need to be flattened and +separated into individual components. For instance, given the GENERIC +expression +</p> +<div class="smallexample"> +<pre class="smallexample">a = b + c +</pre></div> + +<p>its tree representation is: +</p> +<div class="smallexample"> +<pre class="smallexample">MODIFY_EXPR <VAR_DECL <a>, PLUS_EXPR <VAR_DECL <b>, VAR_DECL <c>>> +</pre></div> + +<p>In this case, the GIMPLE form for this statement is logically +identical to its GENERIC form but in GIMPLE, the <code>PLUS_EXPR</code> +on the RHS of the assignment is not represented as a tree, +instead the two operands are taken out of the <code>PLUS_EXPR</code> sub-tree +and flattened into the GIMPLE tuple as follows: +</p> +<div class="smallexample"> +<pre class="smallexample">GIMPLE_ASSIGN <PLUS_EXPR, VAR_DECL <a>, VAR_DECL <b>, VAR_DECL <c>> +</pre></div> + +<a name="Operand-vector-allocation"></a> +<h4 class="subsection">12.6.6 Operand vector allocation</h4> + +<p>The operand vector is stored at the bottom of the three tuple +structures that accept operands. This means, that depending on +the code of a given statement, its operand vector will be at +different offsets from the base of the structure. To access +tuple operands use the following accessors +</p> +<dl> +<dt><a name="index-gimple_005fnum_005fops"></a>GIMPLE function: <em>unsigned</em> <strong>gimple_num_ops</strong> <em>(gimple g)</em></dt> +<dd><p>Returns the number of operands in statement G. +</p></dd></dl> + +<dl> +<dt><a name="index-gimple_005fop"></a>GIMPLE function: <em>tree</em> <strong>gimple_op</strong> <em>(gimple g, unsigned i)</em></dt> +<dd><p>Returns operand <code>I</code> from statement <code>G</code>. +</p></dd></dl> + +<dl> +<dt><a name="index-gimple_005fops"></a>GIMPLE function: <em>tree *</em> <strong>gimple_ops</strong> <em>(gimple g)</em></dt> +<dd><p>Returns a pointer into the operand vector for statement <code>G</code>. This +is computed using an internal table called <code>gimple_ops_offset_</code>[]. +This table is indexed by the gimple code of <code>G</code>. +</p> +<p>When the compiler is built, this table is filled-in using the +sizes of the structures used by each statement code defined in +gimple.def. Since the operand vector is at the bottom of the +structure, for a gimple code <code>C</code> the offset is computed as sizeof +(struct-of <code>C</code>) - sizeof (tree). +</p> +<p>This mechanism adds one memory indirection to every access when +using <code>gimple_op</code>(), if this becomes a bottleneck, a pass can +choose to memoize the result from <code>gimple_ops</code>() and use that to +access the operands. +</p></dd></dl> + +<a name="Operand-validation"></a> +<h4 class="subsection">12.6.7 Operand validation</h4> + +<p>When adding a new operand to a gimple statement, the operand will +be validated according to what each tuple accepts in its operand +vector. These predicates are called by the +<code>gimple_<var>name</var>_set_...()</code>. Each tuple will use one of the +following predicates (Note, this list is not exhaustive): +</p> +<dl> +<dt><a name="index-is_005fgimple_005fval"></a>GIMPLE function: <em>bool</em> <strong>is_gimple_val</strong> <em>(tree t)</em></dt> +<dd><p>Returns true if t is a "GIMPLE value", which are all the +non-addressable stack variables (variables for which +<code>is_gimple_reg</code> returns true) and constants (expressions for which +<code>is_gimple_min_invariant</code> returns true). +</p></dd></dl> + +<dl> +<dt><a name="index-is_005fgimple_005faddressable"></a>GIMPLE function: <em>bool</em> <strong>is_gimple_addressable</strong> <em>(tree t)</em></dt> +<dd><p>Returns true if t is a symbol or memory reference whose address +can be taken. +</p></dd></dl> + +<dl> +<dt><a name="index-is_005fgimple_005fasm_005fval"></a>GIMPLE function: <em>bool</em> <strong>is_gimple_asm_val</strong> <em>(tree t)</em></dt> +<dd><p>Similar to <code>is_gimple_val</code> but it also accepts hard registers. +</p></dd></dl> + +<dl> +<dt><a name="index-is_005fgimple_005fcall_005faddr"></a>GIMPLE function: <em>bool</em> <strong>is_gimple_call_addr</strong> <em>(tree t)</em></dt> +<dd><p>Return true if t is a valid expression to use as the function +called by a <code>GIMPLE_CALL</code>. +</p></dd></dl> + +<dl> +<dt><a name="index-is_005fgimple_005fmem_005fref_005faddr"></a>GIMPLE function: <em>bool</em> <strong>is_gimple_mem_ref_addr</strong> <em>(tree t)</em></dt> +<dd><p>Return true if t is a valid expression to use as first operand +of a <code>MEM_REF</code> expression. +</p></dd></dl> + +<dl> +<dt><a name="index-is_005fgimple_005fconstant"></a>GIMPLE function: <em>bool</em> <strong>is_gimple_constant</strong> <em>(tree t)</em></dt> +<dd><p>Return true if t is a valid gimple constant. +</p></dd></dl> + +<dl> +<dt><a name="index-is_005fgimple_005fmin_005finvariant"></a>GIMPLE function: <em>bool</em> <strong>is_gimple_min_invariant</strong> <em>(tree t)</em></dt> +<dd><p>Return true if t is a valid minimal invariant. This is different +from constants, in that the specific value of t may not be known +at compile time, but it is known that it doesn’t change (e.g., +the address of a function local variable). +</p></dd></dl> + +<dl> +<dt><a name="index-is_005fgimple_005fip_005finvariant"></a>GIMPLE function: <em>bool</em> <strong>is_gimple_ip_invariant</strong> <em>(tree t)</em></dt> +<dd><p>Return true if t is an interprocedural invariant. This means that t +is a valid invariant in all functions (e.g. it can be an address of a +global variable but not of a local one). +</p></dd></dl> + +<dl> +<dt><a name="index-is_005fgimple_005fip_005finvariant_005faddress"></a>GIMPLE function: <em>bool</em> <strong>is_gimple_ip_invariant_address</strong> <em>(tree t)</em></dt> +<dd><p>Return true if t is an <code>ADDR_EXPR</code> that does not change once the +program is running (and which is valid in all functions). +</p></dd></dl> + + +<a name="Statement-validation"></a> +<h4 class="subsection">12.6.8 Statement validation</h4> + +<dl> +<dt><a name="index-is_005fgimple_005fassign"></a>GIMPLE function: <em>bool</em> <strong>is_gimple_assign</strong> <em>(gimple g)</em></dt> +<dd><p>Return true if the code of g is <code>GIMPLE_ASSIGN</code>. +</p></dd></dl> + +<dl> +<dt><a name="index-is_005fgimple_005fcall"></a>GIMPLE function: <em>bool</em> <strong>is_gimple_call</strong> <em>(gimple g)</em></dt> +<dd><p>Return true if the code of g is <code>GIMPLE_CALL</code>. +</p></dd></dl> + +<dl> +<dt><a name="index-is_005fgimple_005fdebug"></a>GIMPLE function: <em>bool</em> <strong>is_gimple_debug</strong> <em>(gimple g)</em></dt> +<dd><p>Return true if the code of g is <code>GIMPLE_DEBUG</code>. +</p></dd></dl> + +<dl> +<dt><a name="index-gimple_005fassign_005fcast_005fp"></a>GIMPLE function: <em>bool</em> <strong>gimple_assign_cast_p</strong> <em>(const_gimple g)</em></dt> +<dd><p>Return true if g is a <code>GIMPLE_ASSIGN</code> that performs a type cast +operation. +</p></dd></dl> + +<dl> +<dt><a name="index-gimple_005fdebug_005fbind_005fp"></a>GIMPLE function: <em>bool</em> <strong>gimple_debug_bind_p</strong> <em>(gimple g)</em></dt> +<dd><p>Return true if g is a <code>GIMPLE_DEBUG</code> that binds the value of an +expression to a variable. +</p></dd></dl> + +<dl> +<dt><a name="index-is_005fgimple_005fomp"></a>GIMPLE function: <em>bool</em> <strong>is_gimple_omp</strong> <em>(gimple g)</em></dt> +<dd><p>Return true if g is any of the OpenMP codes. +</p></dd></dl> + +<dl> +<dt><a name="index-gimple_005fdebug_005fbegin_005fstmt_005fp"></a>GIMPLE function: <em>bool</em> <strong>gimple_debug_begin_stmt_p</strong> <em>(gimple g)</em></dt> +<dd><p>Return true if g is a <code>GIMPLE_DEBUG</code> that marks the beginning of +a source statement. +</p></dd></dl> + +<dl> +<dt><a name="index-gimple_005fdebug_005finline_005fentry_005fp"></a>GIMPLE function: <em>bool</em> <strong>gimple_debug_inline_entry_p</strong> <em>(gimple g)</em></dt> +<dd><p>Return true if g is a <code>GIMPLE_DEBUG</code> that marks the entry +point of an inlined function. +</p></dd></dl> + +<dl> +<dt><a name="index-gimple_005fdebug_005fnonbind_005fmarker_005fp"></a>GIMPLE function: <em>bool</em> <strong>gimple_debug_nonbind_marker_p</strong> <em>(gimple g)</em></dt> +<dd><p>Return true if g is a <code>GIMPLE_DEBUG</code> that marks a program location, +without any variable binding. +</p></dd></dl> + +<hr> +<div class="header"> +<p> +Previous: <a href="Conditional-Expressions.html#Conditional-Expressions" accesskey="p" rel="previous">Conditional Expressions</a>, Up: <a href="Operands.html#Operands" accesskey="u" rel="up">Operands</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> |