AuroraMiddleware/v8
1
0
Fork 0
Code Issues 2 Pull Requests Releases Wiki Activity

[cleanup] Better implementation of SmiTagging<4>::IsValidSmi()

Browse Source 
... which works properly when intptr_t is bigger than int and makes
MSVC happy about this.

Bug: v8:9183
Change-Id: I224eff00c1cbcb9a8c9f16eadaec078db7cf16db
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1601511
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61405}
This commit is contained in:
Igor Sheludko 2019-05-09 16:15:47 +02:00 committed by Commit Bot
parent 0975c55409
commit e96d591e7e
2 changed files with 25 additions and 18 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

41
include/v8-internal.h
View File

@ -48,28 +48,32 @@ const intptr_t kSmiTagMask = (1 << kSmiTagSize) - 1;
template <size_t tagged_ptr_size>
struct SmiTagging;
constexpr intptr_t kIntptrAllBitsSet = intptr_t{-1};
constexpr uintptr_t kUintptrAllBitsSet =
static_cast<uintptr_t>(kIntptrAllBitsSet);
// Smi constants for systems where tagged pointer is a 32-bit value.
template <>
struct SmiTagging<4> {
enum { kSmiShiftSize = 0, kSmiValueSize = 31 };
static constexpr intptr_t kSmiMinValue =
static_cast<intptr_t>(kUintptrAllBitsSet << (kSmiValueSize - 1));
static constexpr intptr_t kSmiMaxValue = -(kSmiMinValue + 1);
V8_INLINE static int SmiToInt(const internal::Address value) {
int shift_bits = kSmiTagSize + kSmiShiftSize;
// Shift down (requires >> to be sign extending).
return static_cast<int>(static_cast<intptr_t>(value)) >> shift_bits;
}
V8_INLINE static constexpr bool IsValidSmi(intptr_t value) {
// To be representable as an tagged small integer, the two
// most-significant bits of 'value' must be either 00 or 11 due to
// sign-extension. To check this we add 01 to the two
// most-significant bits, and check if the most-significant bit is 0.
//
// CAUTION: The original code below:
// bool result = ((value + 0x40000000) & 0x80000000) == 0;
// may lead to incorrect results according to the C language spec, and
// in fact doesn't work correctly with gcc4.1.1 in some cases: The
// compiler may produce undefined results in case of signed integer
// overflow. The computation must be done w/ unsigned ints.
return static_cast<uintptr_t>(value) + 0x40000000U < 0x80000000U;
// Is value in range [kSmiMinValue, kSmiMaxValue].
// Use unsigned operations in order to avoid undefined behaviour in case of
// signed integer overflow.
return (static_cast<uintptr_t>(value) -
static_cast<uintptr_t>(kSmiMinValue)) <=
(static_cast<uintptr_t>(kSmiMaxValue) -
static_cast<uintptr_t>(kSmiMinValue));
}
};
@ -77,6 +81,11 @@ struct SmiTagging<4> {
template <>
struct SmiTagging<8> {
enum { kSmiShiftSize = 31, kSmiValueSize = 32 };
static constexpr intptr_t kSmiMinValue =
static_cast<intptr_t>(kUintptrAllBitsSet << (kSmiValueSize - 1));
static constexpr intptr_t kSmiMaxValue = -(kSmiMinValue + 1);
V8_INLINE static int SmiToInt(const internal::Address value) {
int shift_bits = kSmiTagSize + kSmiShiftSize;
// Shift down and throw away top 32 bits.
@ -98,15 +107,15 @@ const int kApiTaggedSize = kApiSystemPointerSize;
#endif
#ifdef V8_31BIT_SMIS_ON_64BIT_ARCH
typedef SmiTagging<kApiInt32Size> PlatformSmiTagging;
using PlatformSmiTagging = SmiTagging<kApiInt32Size>;
#else
typedef SmiTagging<kApiTaggedSize> PlatformSmiTagging;
using PlatformSmiTagging = SmiTagging<kApiTaggedSize>;
#endif
const int kSmiShiftSize = PlatformSmiTagging::kSmiShiftSize;
const int kSmiValueSize = PlatformSmiTagging::kSmiValueSize;
const int kSmiMinValue = (static_cast<unsigned int>(-1)) << (kSmiValueSize - 1);
const int kSmiMaxValue = -(kSmiMinValue + 1);
const int kSmiMinValue = static_cast<int>(PlatformSmiTagging::kSmiMinValue);
const int kSmiMaxValue = static_cast<int>(PlatformSmiTagging::kSmiMaxValue);
constexpr bool SmiValuesAre31Bits() { return kSmiValueSize == 31; }
constexpr bool SmiValuesAre32Bits() { return kSmiValueSize == 32; }

2
src/globals.h
View File

@ -162,7 +162,6 @@ constexpr size_t kMaxWasmCodeMemory = kMaxWasmCodeMB * MB;
constexpr int kSystemPointerSizeLog2 = 3;
constexpr intptr_t kIntptrSignBit =
static_cast<intptr_t>(uintptr_t{0x8000000000000000});
constexpr uintptr_t kUintptrAllBitsSet = uintptr_t{0xFFFFFFFFFFFFFFFF};
constexpr bool kRequiresCodeRange = true;
#if V8_HOST_ARCH_PPC && V8_TARGET_ARCH_PPC && V8_OS_LINUX
constexpr size_t kMaximalCodeRangeSize = 512 * MB;
@ -184,7 +183,6 @@ constexpr size_t kReservedCodeRangePages = 0;
#else
constexpr int kSystemPointerSizeLog2 = 2;
constexpr intptr_t kIntptrSignBit = 0x80000000;
constexpr uintptr_t kUintptrAllBitsSet = 0xFFFFFFFFu;
#if V8_HOST_ARCH_PPC && V8_TARGET_ARCH_PPC && V8_OS_LINUX
constexpr bool kRequiresCodeRange = false;
constexpr size_t kMaximalCodeRangeSize = 0 * MB;