X87: Fix the sqrt precision issue.

src/x87/codegen-x87.cc

 // Copyright 2012 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/x87/codegen-x87.h"
 
 #if V8_TARGET_ARCH_X87
 
 #include "src/codegen.h"
 #include "src/heap/heap.h"
@@ skipping 23 matching lines @@
 #define __ masm.
 
 
 UnaryMathFunction CreateExpFunction() {
   // No SSE2 support
   return &std::exp;
 }
 
 
 UnaryMathFunction CreateSqrtFunction() {
-  // No SSE2 support
-  return &std::sqrt;
+  size_t actual_size;
+  // Allocate buffer in executable space.
+  byte* buffer =
+      static_cast<byte*>(base::OS::Allocate(1 * KB, &actual_size, true));
+  if (buffer == NULL) return &std::sqrt;
+
+  MacroAssembler masm(NULL, buffer, static_cast<int>(actual_size));
+  // Load double input into registers.
+  __ fld_d(MemOperand(esp, 4));
+  __ X87SetFPUCW(0x027F);
+  __ fsqrt();
+  __ X87SetFPUCW(0x037F);
+  __ Ret();
+
+  CodeDesc desc;
+  masm.GetCode(&desc);
+  DCHECK(!RelocInfo::RequiresRelocation(desc));
+
+  Assembler::FlushICacheWithoutIsolate(buffer, actual_size);
+  base::OS::ProtectCode(buffer, actual_size);
+  return FUNCTION_CAST<UnaryMathFunction>(buffer);
 }
 
 
 // Helper functions for CreateMemMoveFunction.
 #undef __
 #define __ ACCESS_MASM(masm)
 
 enum Direction { FORWARD, BACKWARD };
 enum Alignment { MOVE_ALIGNED, MOVE_UNALIGNED };
 
@@ skipping 567 matching lines @@
     CodePatcher patcher(sequence, young_length);
     patcher.masm()->call(stub->instruction_start(), RelocInfo::NONE32);
   }
 }
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_X87