[wasm] Detect unrepresentability in the float32-to-int32 conversion correctly on arm.

src/compiler/arm64/code-generator-arm64.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/compiler/code-generator.h"
 
 #include "src/arm64/frames-arm64.h"
 #include "src/arm64/macro-assembler-arm64.h"
 #include "src/ast/scopes.h"
 #include "src/compiler/code-generator-impl.h"
@@ skipping 1305 matching lines @@
       __ Fsqrt(i.OutputDoubleRegister(), i.InputDoubleRegister(0));
       break;
     case kArm64Float32ToFloat64:
       __ Fcvt(i.OutputDoubleRegister(), i.InputDoubleRegister(0).S());
       break;
     case kArm64Float64ToFloat32:
       __ Fcvt(i.OutputDoubleRegister().S(), i.InputDoubleRegister(0));
       break;
     case kArm64Float32ToInt32:
       __ Fcvtzs(i.OutputRegister32(), i.InputFloat32Register(0));
+      // Avoid INT32_MAX as an overflow indicator and use INT32_MIN instead,
+      // because INT32_MIN allows easier out-of-bounds detection.
+      __ Cmn(i.OutputRegister32(), 1);
+      __ Csinc(i.OutputRegister32(), i.OutputRegister32(), i.OutputRegister32(),
+               vc);
       break;
     case kArm64Float64ToInt32:
       __ Fcvtzs(i.OutputRegister32(), i.InputDoubleRegister(0));
       break;
     case kArm64Float32ToUint32:
       __ Fcvtzu(i.OutputRegister32(), i.InputFloat32Register(0));
+      // Avoid UINT32_MAX as an overflow indicator and use 0 instead,
+      // because 0 allows easier out-of-bounds detection.
+      __ Cmn(i.OutputRegister32(), 1);
+      __ Adc(i.OutputRegister(), i.OutputRegister(), Operand(0));

[Rodolph Perfetta (ARM), 2016/06/29 15:42:18]

i.OutputRegister32(), I made the mistake in my previous suggestion.

[ahaas, 2016/06/29 15:49:53]

Done. Thanks for looking at it so carefully again.

       break;
     case kArm64Float64ToUint32:
       __ Fcvtzu(i.OutputRegister32(), i.InputDoubleRegister(0));
       break;
     case kArm64Float32ToInt64:
       __ Fcvtzs(i.OutputRegister64(), i.InputFloat32Register(0));
       if (i.OutputCount() > 1) {
         __ Mov(i.OutputRegister(1), 1);
         Label done;
         __ Cmp(i.OutputRegister(0), 1);
@@ skipping 645 matching lines @@
       padding_size -= kInstructionSize;
     }
   }
 }
 
 #undef __
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8