1; RUN: llc < %s -march=x86-64 -verify-machineinstrs | FileCheck %s --check-prefix=CHECK --check-prefix=X64 2; RUN: llc < %s -march=x86 -mattr=+sse2 -verify-machineinstrs | FileCheck %s --check-prefix=CHECK --check-prefix=X32 3 4; On x86, an atomic rmw operation that does not modify the value in memory 5; (such as atomic add 0) can be replaced by an mfence followed by a mov. 6; This is explained (with the motivation for such an optimization) in 7; http://www.hpl.hp.com/techreports/2012/HPL-2012-68.pdf 8 9define i8 @add8(i8* %p) { 10; CHECK-LABEL: add8 11; CHECK: mfence 12; CHECK: movb 13 %1 = atomicrmw add i8* %p, i8 0 monotonic 14 ret i8 %1 15} 16 17define i16 @or16(i16* %p) { 18; CHECK-LABEL: or16 19; CHECK: mfence 20; CHECK: movw 21 %1 = atomicrmw or i16* %p, i16 0 acquire 22 ret i16 %1 23} 24 25define i32 @xor32(i32* %p) { 26; CHECK-LABEL: xor32 27; CHECK: mfence 28; CHECK: movl 29 %1 = atomicrmw xor i32* %p, i32 0 release 30 ret i32 %1 31} 32 33define i64 @sub64(i64* %p) { 34; CHECK-LABEL: sub64 35; X64: mfence 36; X64: movq 37; X32-NOT: mfence 38 %1 = atomicrmw sub i64* %p, i64 0 seq_cst 39 ret i64 %1 40} 41 42define i128 @or128(i128* %p) { 43; CHECK-LABEL: or128 44; CHECK-NOT: mfence 45 %1 = atomicrmw or i128* %p, i128 0 monotonic 46 ret i128 %1 47} 48 49; For 'and', the idempotent value is (-1) 50define i32 @and32 (i32* %p) { 51; CHECK-LABEL: and32 52; CHECK: mfence 53; CHECK: movl 54 %1 = atomicrmw and i32* %p, i32 -1 acq_rel 55 ret i32 %1 56} 57