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| author | Noah Misch <noah@leadboat.com> | 2019-10-18 20:20:28 -0700 |
|---|---|---|
| committer | Noah Misch <noah@leadboat.com> | 2019-10-18 20:20:32 -0700 |
| commit | af4477b00cf93c8305aebe3b58ea26499664336e (patch) | |
| tree | 973ddd63166394cbe30c256cebe7726d0f9791cb | |
| parent | f7b70700bc44d4a7e5de143c6906e2421dd0c709 (diff) | |
| download | postgresql-af4477b00cf93c8305aebe3b58ea26499664336e.tar.gz postgresql-af4477b00cf93c8305aebe3b58ea26499664336e.zip | |
For PowerPC instruction "addi", use constraint "b".
Without "b", a variant of the tas() code miscompiles on macOS 10.4.
This may also fix a compilation failure involving macOS 10.1. Today's
compilers have been allocating acceptable registers with or without this
change, but this future-proofs the code by precisely conveying the
acceptable registers. Back-patch to 9.4 (all supported versions).
Reviewed by Tom Lane.
Discussion: https://postgr.es/m/20191009063900.GA4066266@rfd.leadboat.com
| -rw-r--r-- | src/include/storage/s_lock.h | 7 |
1 files changed, 6 insertions, 1 deletions
diff --git a/src/include/storage/s_lock.h b/src/include/storage/s_lock.h index 7ec32c1e6fb..eebfe890f03 100644 --- a/src/include/storage/s_lock.h +++ b/src/include/storage/s_lock.h @@ -452,6 +452,11 @@ typedef unsigned int slock_t; #define TAS_SPIN(lock) (*(lock) ? 1 : TAS(lock)) /* + * The second operand of addi can hold a constant zero or a register number, + * hence constraint "=&b" to avoid allocating r0. "b" stands for "address + * base register"; most operands having this register-or-zero property are + * address bases, e.g. the second operand of lwax. + * * NOTE: per the Enhanced PowerPC Architecture manual, v1.0 dated 7-May-2002, * an isync is a sufficient synchronization barrier after a lwarx/stwcx loop. * On newer machines, we can use lwsync instead for better performance. @@ -488,7 +493,7 @@ tas(volatile slock_t *lock) #endif " li %1,0 \n" -: "=&r"(_t), "=r"(_res), "+m"(*lock) +: "=&b"(_t), "=r"(_res), "+m"(*lock) : "r"(lock) : "memory", "cc"); return _res; |