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[AArch64] Don't replace dst of SWP instructions with (X|W)ZR #102139

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Aug 7, 2024
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[AArch64] Don't replace dst of SWP instructions with (X|W)ZR #102139

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4 changes: 4 additions & 0 deletions llvm/lib/Target/AArch64/AArch64DeadRegisterDefinitionsPass.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -108,6 +108,10 @@ static bool atomicReadDroppedOnZero(unsigned Opcode) {
case AArch64::LDUMINW: case AArch64::LDUMINX:
case AArch64::LDUMINLB: case AArch64::LDUMINLH:
case AArch64::LDUMINLW: case AArch64::LDUMINLX:
case AArch64::SWPB: case AArch64::SWPH:
case AArch64::SWPW: case AArch64::SWPX:
case AArch64::SWPLB: case AArch64::SWPLH:
case AArch64::SWPLW: case AArch64::SWPLX:
return true;
}
return false;
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64 changes: 64 additions & 0 deletions llvm/test/CodeGen/AArch64/Atomics/aarch64-atomic-exchange-fence.ll
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Original file line number Diff line number Diff line change
@@ -0,0 +1,64 @@
; RUN: llc %s -o - -verify-machineinstrs -mtriple=aarch64 -mattr=+lse -O0 | FileCheck %s
; RUN: llc %s -o - -verify-machineinstrs -mtriple=aarch64 -mattr=+lse -O1 | FileCheck %s

; When their destination register is WZR/ZZR, SWP operations are not regarded as
; a read for the purpose of a DMB.LD in the AArch64 memory model.
; This test ensures that the AArch64DeadRegisterDefinitions pass does not
; replace the desitnation register of SWP instructions with the zero register
; when the read value is unused.

define dso_local i32 @atomic_exchange_monotonic(ptr %ptr, ptr %ptr2, i32 %value) {
; CHECK-LABEL: atomic_exchange_monotonic:
; CHECK: // %bb.0:
; CHECK-NEXT: swp
; CHECK-NOT: wzr
; CHECK-NEXT: dmb ishld
; CHECK-NEXT: ldr w0, [x1]
; CHECK-NEXT: ret
%r0 = atomicrmw xchg ptr %ptr, i32 %value monotonic
fence acquire
%r1 = load atomic i32, ptr %ptr2 monotonic, align 4
ret i32 %r1
}

define dso_local i32 @atomic_exchange_acquire(ptr %ptr, ptr %ptr2, i32 %value) {
; CHECK-LABEL: atomic_exchange_acquire:
; CHECK: // %bb.0:
; CHECK-NEXT: swpa
; CHECK-NOT: wzr
; CHECK-NEXT: dmb ishld
; CHECK-NEXT: ldr w0, [x1]
; CHECK-NEXT: ret
%r0 = atomicrmw xchg ptr %ptr, i32 %value acquire
fence acquire
%r1 = load atomic i32, ptr %ptr2 monotonic, align 4
ret i32 %r1
}

define dso_local i32 @atomic_exchange_release(ptr %ptr, ptr %ptr2, i32 %value) {
; CHECK-LABEL: atomic_exchange_release:
; CHECK: // %bb.0:
; CHECK-NEXT: swpl
; CHECK-NOT: wzr
; CHECK-NEXT: dmb ishld
; CHECK-NEXT: ldr w0, [x1]
; CHECK-NEXT: ret
%r0 = atomicrmw xchg ptr %ptr, i32 %value release
fence acquire
%r1 = load atomic i32, ptr %ptr2 monotonic, align 4
ret i32 %r1
}

define dso_local i32 @atomic_exchange_acquire_release(ptr %ptr, ptr %ptr2, i32 %value) {
; CHECK-LABEL: atomic_exchange_acquire_release:
; CHECK: // %bb.0:
; CHECK-NEXT: swpal
; CHECK-NOT: wzr
; CHECK-NEXT: dmb ishld
; CHECK-NEXT: ldr w0, [x1]
; CHECK-NEXT: ret
%r0 = atomicrmw xchg ptr %ptr, i32 %value acq_rel
fence acquire
%r1 = load atomic i32, ptr %ptr2 monotonic, align 4
ret i32 %r1
}
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