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gcc/x86{,_64}/ck_pr: improve codegen for compare-and-swap, particularly on GCC6+

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1. For ck_pr_cas_foo_value, let the inline assembly save the observed
   value in a register, and store to the output reference in C.
   This lets the C optimiser eliminate the memory access once the
   CAS function is inlined.

2. Specify the result of the CAS as a condition code in EFLAGS instead
   of executing SETcc in inline assembly, when possible.  GCC gained
   this functionality in GCC 6; CAS loops can now directly branch on
   the condition code, without SETcc / TEST.

TESTED=existing regression tests.
awsm
Paul Khuong 5 years ago committed by Samy Al Bahra
parent 571bb264b0
commit e18fba64ec
2 changed files with 98 additions and 32 deletions
Show Stats Download Patch File Download Diff File

63
include/gcc/x86/ck_pr.h
Unescape View File

@ -309,6 +309,22 @@ CK_PR_GENERATE(xor)
/*
* Atomic compare and swap.
*/
#ifdef __GCC_ASM_FLAG_OUTPUTS__
#define CK_PR_CAS(S, M, T, C, I) \
CK_CC_INLINE static bool \
ck_pr_cas_##S(M *target, T compare, T set) \
{ \
bool z; \
__asm__ __volatile__(CK_PR_LOCK_PREFIX I " %3, %0" \
: "+m" (*(C *)target), \
"=@ccz" (z), \
/* RAX is clobbered by cmpxchg. */ \
"+a" (compare) \
: "q" (set) \
: "memory", "cc"); \
return z; \
}
#else
#define CK_PR_CAS(S, M, T, C, I) \
CK_CC_INLINE static bool \
ck_pr_cas_##S(M *target, T compare, T set) \
@ -322,6 +338,7 @@ CK_PR_GENERATE(xor)
: "memory", "cc"); \
return z; \
}
#endif
CK_PR_CAS(ptr, void, void *, char, "cmpxchgl")
@ -340,34 +357,50 @@ CK_PR_CAS_S(8, uint8_t, "cmpxchgb")
/*
* Compare and swap, set *v to old value of target.
*/
#define CK_PR_CAS_O(S, M, T, C, I, R) \
#ifdef __GCC_ASM_FLAG_OUTPUTS__
#define CK_PR_CAS_O(S, M, T, C, I) \
CK_CC_INLINE static bool \
ck_pr_cas_##S##_value(M *target, T compare, T set, M *v) \
{ \
bool z; \
__asm__ __volatile__(CK_PR_LOCK_PREFIX "cmpxchg" I " %3, %0;" \
: "+m" (*(C *)target), \
"=@ccz" (z), \
"+a" (compare) \
: "q" (set) \
: "memory", "cc"); \
*(T *)v = compare; \
return z; \
}
#else
#define CK_PR_CAS_O(S, M, T, C, I) \
CK_CC_INLINE static bool \
ck_pr_cas_##S##_value(M *target, T compare, T set, M *v) \
{ \
bool z; \
__asm__ __volatile__(CK_PR_LOCK_PREFIX "cmpxchg" I " %3, %0;" \
"mov %% " R ", %2;" \
"setz %1;" \
: "+m" (*(C *)target), \
"=a" (z), \
"=m" (*(C *)v) \
: "q" (set), \
"a" (compare) \
"=q" (z), \
"+a" (compare) \
: "q" (set) \
: "memory", "cc"); \
*(T *)v = compare; \
return z; \
}
#endif
CK_PR_CAS_O(ptr, void, void *, char, "l", "eax")
CK_PR_CAS_O(ptr, void, void *, char, "l")
#define CK_PR_CAS_O_S(S, T, I, R) \
CK_PR_CAS_O(S, T, T, T, I, R)
#define CK_PR_CAS_O_S(S, T, I) \
CK_PR_CAS_O(S, T, T, T, I)
CK_PR_CAS_O_S(char, char, "b", "al")
CK_PR_CAS_O_S(int, int, "l", "eax")
CK_PR_CAS_O_S(uint, unsigned int, "l", "eax")
CK_PR_CAS_O_S(32, uint32_t, "l", "eax")
CK_PR_CAS_O_S(16, uint16_t, "w", "ax")
CK_PR_CAS_O_S(8, uint8_t, "b", "al")
CK_PR_CAS_O_S(char, char, "b")
CK_PR_CAS_O_S(int, int, "l")
CK_PR_CAS_O_S(uint, unsigned int, "l")
CK_PR_CAS_O_S(32, uint32_t, "l")
CK_PR_CAS_O_S(16, uint16_t, "w")
CK_PR_CAS_O_S(8, uint8_t, "b")
#undef CK_PR_CAS_O_S
#undef CK_PR_CAS_O

67
include/gcc/x86_64/ck_pr.h
Unescape View File

@ -410,6 +410,22 @@ CK_PR_GENERATE(xor)
/*
* Atomic compare and swap.
*/
#ifdef __GCC_ASM_FLAG_OUTPUTS__
#define CK_PR_CAS(S, M, T, C, I) \
CK_CC_INLINE static bool \
ck_pr_cas_##S(M *target, T compare, T set) \
{ \
bool z; \
__asm__ __volatile__(CK_PR_LOCK_PREFIX I " %3, %0" \
: "+m" (*(C *)target), \
"=@ccz" (z), \
/* RAX is clobbered by cmpxchg. */ \
"+a" (compare) \
: "q" (set) \
: "memory", "cc"); \
return z; \
}
#else
#define CK_PR_CAS(S, M, T, C, I) \
CK_CC_INLINE static bool \
ck_pr_cas_##S(M *target, T compare, T set) \
@ -423,6 +439,7 @@ CK_PR_GENERATE(xor)
: "memory", "cc"); \
return z; \
}
#endif
CK_PR_CAS(ptr, void, void *, char, "cmpxchgq")
@ -445,38 +462,54 @@ CK_PR_CAS_S(8, uint8_t, "cmpxchgb")
/*
* Compare and swap, set *v to old value of target.
*/
#define CK_PR_CAS_O(S, M, T, C, I, R) \
#ifdef __GCC_ASM_FLAG_OUTPUTS__
#define CK_PR_CAS_O(S, M, T, C, I) \
CK_CC_INLINE static bool \
ck_pr_cas_##S##_value(M *target, T compare, T set, M *v) \
{ \
bool z; \
__asm__ __volatile__(CK_PR_LOCK_PREFIX "cmpxchg" I " %3, %0;" \
: "+m" (*(C *)target), \
"=@ccz" (z), \
"+a" (compare) \
: "q" (set) \
: "memory", "cc"); \
*(T *)v = compare; \
return z; \
}
#else
#define CK_PR_CAS_O(S, M, T, C, I) \
CK_CC_INLINE static bool \
ck_pr_cas_##S##_value(M *target, T compare, T set, M *v) \
{ \
bool z; \
__asm__ __volatile__(CK_PR_LOCK_PREFIX "cmpxchg" I " %3, %0;" \
"mov %% " R ", %2;" \
"setz %1;" \
: "+m" (*(C *)target), \
"=a" (z), \
"=m" (*(C *)v) \
: "q" (set), \
"a" (compare) \
"=q" (z), \
"+a" (compare) \
: "q" (set) \
: "memory", "cc"); \
*(T *)v = compare; \
return z; \
}
#endif
CK_PR_CAS_O(ptr, void, void *, char, "q", "rax")
CK_PR_CAS_O(ptr, void, void *, char, "q")
#define CK_PR_CAS_O_S(S, T, I, R) \
CK_PR_CAS_O(S, T, T, T, I, R)
#define CK_PR_CAS_O_S(S, T, I) \
CK_PR_CAS_O(S, T, T, T, I)
CK_PR_CAS_O_S(char, char, "b", "al")
CK_PR_CAS_O_S(int, int, "l", "eax")
CK_PR_CAS_O_S(uint, unsigned int, "l", "eax")
CK_PR_CAS_O_S(char, char, "b")
CK_PR_CAS_O_S(int, int, "l")
CK_PR_CAS_O_S(uint, unsigned int, "l")
#ifndef CK_PR_DISABLE_DOUBLE
CK_PR_CAS_O_S(double, double, "q", "rax")
CK_PR_CAS_O_S(double, double, "q")
#endif
CK_PR_CAS_O_S(64, uint64_t, "q", "rax")
CK_PR_CAS_O_S(32, uint32_t, "l", "eax")
CK_PR_CAS_O_S(16, uint16_t, "w", "ax")
CK_PR_CAS_O_S(8, uint8_t, "b", "al")
CK_PR_CAS_O_S(64, uint64_t, "q")
CK_PR_CAS_O_S(32, uint32_t, "l")
CK_PR_CAS_O_S(16, uint16_t, "w")
CK_PR_CAS_O_S(8, uint8_t, "b")
#undef CK_PR_CAS_O_S
#undef CK_PR_CAS_O

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