Turbofan: Modify WASM linkage to store floats using only 4 bytes.

test/cctest/compiler/test-run-native-calls.cc

 // Copyright 2015 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/assembler.h"
 #include "src/codegen.h"
 #include "src/compiler/linkage.h"
 #include "src/compiler/raw-machine-assembler.h"
 #include "src/machine-type.h"
 #include "src/register-configuration.h"
@@ skipping 136 matching lines @@
       if (gp_offset < gp_count) {
         return LinkageLocation::ForRegister(gp_regs[gp_offset++]);
       } else {
         int offset = -1 - stack_offset;
         stack_offset += StackWords(type);
         return LinkageLocation::ForCallerFrameSlot(offset);
       }
     }
   }
   int StackWords(MachineType type) {
-    // TODO(titzer): hack. float32 occupies 8 bytes on stack.
-    int size = IsFloatingPoint(type.representation())
-                   ? kDoubleSize
-                   : (1 << ElementSizeLog2Of(type.representation()));
+    int size = 1 << ElementSizeLog2Of(type.representation());
     return size <= kPointerSize ? 1 : size / kPointerSize;
   }
   void Reset() {
     fp_offset = 0;
     gp_offset = 0;
     stack_offset = 0;
   }
 };
 
 
@@ skipping 1087 matching lines @@
   TestStackSlot(MachineType::Float32(), magic);
 }
 
 TEST(RunStackSlotFloat64) {
   double magic = 3456.375;
   TestStackSlot(MachineType::Float64(), magic);
 }
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8