[turbofan] Add support for overflow add/sub to the MachineOperatorReducer.

src/base/bits.h

 // 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.
 
 #ifndef V8_BASE_BITS_H_
 #define V8_BASE_BITS_H_
 
 #include "include/v8stdint.h"
+#include "src/base/macros.h"
 #if V8_CC_MSVC
 #include <intrin.h>
 #endif
 #if V8_OS_WIN32
 #include "src/base/win32-headers.h"
 #endif
 
 namespace v8 {
 namespace base {
 namespace bits {
@@ skipping 88 matching lines @@
   if (shift == 0) return value;
   return (value >> shift) | (value << (32 - shift));
 }
 
 
 inline uint64_t RotateRight64(uint64_t value, uint64_t shift) {
   if (shift == 0) return value;
   return (value >> shift) | (value << (64 - shift));
 }
 
+
+// SignedAddOverflow32(lhs,rhs,val) performs a signed summation of |lhs| and
+// |rhs| and stores the result into the variable pointed to by |val| and
+// returns true if the signed summation resulted in an overflow.
+inline bool SignedAddOverflow32(int32_t lhs, int32_t rhs, int32_t* val) {
+#if V8_HAS_BUILTIN_SADD_OVERFLOW
+  return __builtin_sadd_overflow(lhs, rhs, val);
+#else
+  uint32_t res = static_cast<uint32_t>(lhs) + static_cast<uint32_t>(rhs);
+  *val = bit_cast<int32_t>(res);
+  return (((res ^ lhs) & (res ^ rhs)) >> 31) & 1;

[Sven Panne, 2014/09/09 13:10:48]

I think that

   return (((res ^ lhs) & (res ^ rhs) & (1U << 31)) != 0;

is a bit clearer and involves no implicit conversion, similar below.

[Benedikt Meurer, 2014/09/09 14:15:23]

Done.

+#endif
+}
+
+
+// SignedSubOverflow32(lhs,rhs,val) performs a signed subtraction of |lhs| and
+// |rhs| and stores the result into the variable pointed to by |val| and
+// returns true if the signed subtraction resulted in an overflow.
+inline bool SignedSubOverflow32(int32_t lhs, int32_t rhs, int32_t* val) {
+#if V8_HAS_BUILTIN_SSUB_OVERFLOW
+  return __builtin_ssub_overflow(lhs, rhs, val);
+#else
+  uint32_t res = static_cast<uint32_t>(lhs) - static_cast<uint32_t>(rhs);
+  *val = bit_cast<int32_t>(res);
+  return (((res ^ lhs) & (res ^ ~rhs)) >> 31) & 1;
+#endif
+}
+
 }  // namespace bits
 }  // namespace base
 }  // namespace v8
 
 #endif  // V8_BASE_BITS_H_