[view compiler] Add conditional branch instruction

This CL adds support for the if-eqz instruction. It should be easy to add
additional comparisons as needed.

This also introduces a new kind of Value called a Label. Labels may be created
any time and then must be bound to a location in code at some point. References
to labels are tracked, and when a label is bound all references are patched to
refer to the concrete address.

Bug: 111895153
Change-Id: I15424aec75425004f0f1f4bbc6e760bac3a6c7de

1 files changed, 75 insertions, 7 deletions

diff --git a/startop/view_compiler/dex_testcase_generator.cc b/startop/view_compiler/dex_testcase_generator.cc
index 898817b4768c..c521bf2b8ccf 100644
--- a/startop/view_compiler/dex_testcase_generator.cc
+++ b/startop/view_compiler/dex_testcase_generator.cc
@@ -46,9 +46,11 @@ void GenerateSimpleTestCases(const string& outdir) {
 
   // int return5() { return 5; }
   auto return5{cbuilder.CreateMethod("return5", Prototype{TypeDescriptor::Int()})};
-  Value r{return5.MakeRegister()};
-  return5.BuildConst4(r, 5);
-  return5.BuildReturn(r);
+  {
+    Value r{return5.MakeRegister()};
+    return5.BuildConst4(r, 5);
+    return5.BuildReturn(r);
+  }
   return5.Encode();
 
   // // int returnParam(int x) { return x; }
@@ -64,12 +66,78 @@ void GenerateSimpleTestCases(const string& outdir) {
 
   auto returnStringLength{
       cbuilder.CreateMethod("returnStringLength", Prototype{TypeDescriptor::Int(), string_type})};
-  Value result = returnStringLength.MakeRegister();
-  returnStringLength.AddInstruction(
-      Instruction::InvokeVirtual(string_length.id, result, Value::Parameter(0)));
-  returnStringLength.BuildReturn(result);
+  {
+    Value result = returnStringLength.MakeRegister();
+    returnStringLength.AddInstruction(
+        Instruction::InvokeVirtual(string_length.id, result, Value::Parameter(0)));
+    returnStringLength.BuildReturn(result);
+  }
   returnStringLength.Encode();
 
+  // int returnIfZero(int x) { if (x == 0) { return 5; } else { return 3; } }
+  MethodBuilder returnIfZero{cbuilder.CreateMethod(
+      "returnIfZero", Prototype{TypeDescriptor::Int(), TypeDescriptor::Int()})};
+  {
+    Value resultIfZero{returnIfZero.MakeRegister()};
+    Value else_target{returnIfZero.MakeLabel()};
+    returnIfZero.AddInstruction(Instruction::OpWithArgs(
+        Instruction::Op::kBranchEqz, /*dest=*/{}, Value::Parameter(0), else_target));
+    // else branch
+    returnIfZero.BuildConst4(resultIfZero, 3);
+    returnIfZero.AddInstruction(
+        Instruction::OpWithArgs(Instruction::Op::kReturn, /*dest=*/{}, resultIfZero));
+    // then branch
+    returnIfZero.AddInstruction(
+        Instruction::OpWithArgs(Instruction::Op::kBindLabel, /*dest=*/{}, else_target));
+    returnIfZero.BuildConst4(resultIfZero, 5);
+    returnIfZero.AddInstruction(
+        Instruction::OpWithArgs(Instruction::Op::kReturn, /*dest=*/{}, resultIfZero));
+  }
+  returnIfZero.Encode();
+
+  // Make sure backwards branches work too.
+  //
+  // Pseudo code for test:
+  // {
+  //   zero = 0;
+  //   result = 1;
+  //   if (zero == 0) goto B;
+  // A:
+  //   return result;
+  // B:
+  //   result = 2;
+  //   if (zero == 0) goto A;
+  //   result = 3;
+  //   return result;
+  // }
+  // If it runs correctly, this test should return 2.
+  MethodBuilder backwardsBranch{
+      cbuilder.CreateMethod("backwardsBranch", Prototype{TypeDescriptor::Int()})};
+  [](MethodBuilder& method) {
+    Value zero = method.MakeRegister();
+    Value result = method.MakeRegister();
+    Value labelA = method.MakeLabel();
+    Value labelB = method.MakeLabel();
+    method.BuildConst4(zero, 0);
+    method.BuildConst4(result, 1);
+    method.AddInstruction(
+        Instruction::OpWithArgs(Instruction::Op::kBranchEqz, /*dest=*/{}, zero, labelB));
+
+    method.AddInstruction(
+        Instruction::OpWithArgs(Instruction::Op::kBindLabel, /*dest=*/{}, labelA));
+    method.BuildReturn(result);
+
+    method.AddInstruction(
+        Instruction::OpWithArgs(Instruction::Op::kBindLabel, /*dest=*/{}, labelB));
+    method.BuildConst4(result, 2);
+    method.AddInstruction(
+        Instruction::OpWithArgs(Instruction::Op::kBranchEqz, /*dest=*/{}, zero, labelA));
+
+    method.BuildConst4(result, 3);
+    method.BuildReturn(result);
+  }(backwardsBranch);
+  backwardsBranch.Encode();
+
   slicer::MemView image{dex_file.CreateImage()};
   std::ofstream out_file(outdir + "/simple.dex");
   out_file.write(image.ptr<const char>(), image.size());