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[ptr-compr] Use __builtin_assume_aligned() when available

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... to let C++ compiler know that isolate root is 4Gb aligned and give
it a chance to generate a better code.

Bug: v8:9353
Change-Id: Ibd23c14cc44107c722a446a84dd14ca66f3bccfe
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1776079
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63445}
This commit is contained in:
Igor Sheludko 2019-08-29 13:14:02 +02:00 committed by Commit Bot
parent 2e0bc516b7
commit fe7b3f9dbb
2 changed files with 14 additions and 1 deletions
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8
include/v8config.h
View File

@ -216,6 +216,7 @@
# define V8_HAS_ATTRIBUTE_WARN_UNUSED_RESULT \
(__has_attribute(warn_unused_result))
# define V8_HAS_BUILTIN_ASSUME_ALIGNED (__has_builtin(__builtin_assume_aligned))
# define V8_HAS_BUILTIN_BSWAP16 (__has_builtin(__builtin_bswap16))
# define V8_HAS_BUILTIN_BSWAP32 (__has_builtin(__builtin_bswap32))
# define V8_HAS_BUILTIN_BSWAP64 (__has_builtin(__builtin_bswap64))
@ -262,6 +263,7 @@
# define V8_HAS_ATTRIBUTE_WARN_UNUSED_RESULT \
(!V8_CC_INTEL && V8_GNUC_PREREQ(4, 1, 0))
# define V8_HAS_BUILTIN_ASSUME_ALIGNED (V8_GNUC_PREREQ(4, 7, 0))
# define V8_HAS_BUILTIN_CLZ (V8_GNUC_PREREQ(3, 4, 0))
# define V8_HAS_BUILTIN_CTZ (V8_GNUC_PREREQ(3, 4, 0))
# define V8_HAS_BUILTIN_EXPECT (V8_GNUC_PREREQ(2, 96, 0))
@ -300,6 +302,12 @@
# define V8_INLINE inline
#endif
#if V8_HAS_BUILTIN_ASSUME_ALIGNED
# define V8_ASSUME_ALIGNED(ptr, alignment) \
__builtin_assume_aligned((ptr), (alignment))
#else
# define V8_ASSUME_ALIGNED(ptr) (ptr)
#endif
// A macro used to tell the compiler to never inline a particular function.
// Don't bother for debug builds.

7
src/common/ptr-compr-inl.h
View File

@ -35,7 +35,12 @@ V8_INLINE Address GetIsolateRoot<Address>(Address on_heap_addr) {
template <>
V8_INLINE Address GetIsolateRoot<Isolate*>(Isolate* isolate) {
return isolate->isolate_root();
Address isolate_root = isolate->isolate_root();
#ifdef V8_COMPRESS_POINTERS
isolate_root = reinterpret_cast<Address>(V8_ASSUME_ALIGNED(
reinterpret_cast<void*>(isolate_root), kPtrComprIsolateRootAlignment));
#endif
return isolate_root;
}
// Decompresses smi value.