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[GlobalISel] Clear nsw flags when converting sub to add. #137288

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Merged
davemgreen merged 1 commit into from
Apr 26, 2025
Merged

[GlobalISel] Clear nsw flags when converting sub to add. #137288

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2 changes: 2 additions & 0 deletions llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2112,6 +2112,8 @@ bool CombinerHelper::matchCombineSubToAdd(MachineInstr &MI,
MI.setDesc(B.getTII().get(TargetOpcode::G_ADD));
MI.getOperand(2).setReg(NegCst.getReg(0));
MI.clearFlag(MachineInstr::MIFlag::NoUWrap);
if (Imm.isMinSignedValue())
MI.clearFlags(MachineInstr::MIFlag::NoSWrap);
Observer.changedInstr(MI);
};
return true;
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45 changes: 45 additions & 0 deletions llvm/test/CodeGen/AArch64/GlobalISel/prelegalizercombiner-trivial-arith.mir
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Expand Up @@ -551,3 +551,48 @@ body: |
RET_ReallyLR implicit $w0

...
---
name: sub_to_add_nsw_128
body: |
bb.0:
liveins: $w0, $w1

; CHECK-LABEL: name: sub_to_add_nsw_128
; CHECK: liveins: $w0, $w1
; CHECK-NEXT: {{ $}}
; CHECK-NEXT: %a:_(s32) = COPY $w0
; CHECK-NEXT: %b:_(s8) = G_TRUNC %a(s32)
; CHECK-NEXT: %c:_(s8) = G_CONSTANT i8 -128
; CHECK-NEXT: %add:_(s8) = G_ADD %b, %c
; CHECK-NEXT: %d:_(s32) = G_ZEXT %add(s8)
; CHECK-NEXT: $w0 = COPY %d(s32)
; CHECK-NEXT: RET_ReallyLR implicit $x0
%a:_(s32) = COPY $w0
%b:_(s8) = G_TRUNC %a
%c:_(s8) = G_CONSTANT i8 -128
%add:_(s8) = nsw nuw G_SUB %b, %c
%d:_(s32) = G_ZEXT %add
$w0 = COPY %d
RET_ReallyLR implicit $x0

...
---
name: sub_to_add_nsw_intmin
body: |
bb.0:
liveins: $w0, $w1

; CHECK-LABEL: name: sub_to_add_nsw_intmin
; CHECK: liveins: $w0, $w1
; CHECK-NEXT: {{ $}}
; CHECK-NEXT: %a:_(s32) = COPY $w0
; CHECK-NEXT: %c:_(s32) = G_CONSTANT i32 -2147483648
; CHECK-NEXT: %add:_(s32) = G_ADD %a, %c
; CHECK-NEXT: $w0 = COPY %add(s32)
; CHECK-NEXT: RET_ReallyLR implicit $x0
%a:_(s32) = COPY $w0
%c:_(s32) = G_CONSTANT i32 -2147483648
%add:_(s32) = nsw nuw G_SUB %a, %c
$w0 = COPY %add
RET_ReallyLR implicit $x0
...
14 changes: 14 additions & 0 deletions llvm/test/CodeGen/AArch64/sub1.ll
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Expand Up @@ -117,3 +117,17 @@ define <4 x i32> @masked_sub_v4i32(<4 x i32> %x) {
%m = sub <4 x i32> <i32 511, i32 511, i32 511, i32 511>, %a
ret <4 x i32> %m
}

define i32 @pr137254(i32 %0) {
; CHECK-LABEL: pr137254:
; CHECK: // %bb.0:
; CHECK-NEXT: mov w8, #-2147483648 // =0x80000000
; CHECK-NEXT: add w8, w0, w8
; CHECK-NEXT: cmp w8, #0
; CHECK-NEXT: cset w0, gt
; CHECK-NEXT: ret
%2 = sub nsw i32 %0, -2147483648
%3 = icmp sgt i32 %2, 0
%4 = select i1 %3, i32 1, i32 0
ret i32 %4
}
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