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[DAG] SimplifyDemandedBits - ensure we drop NSW/NUW flags when we simplify a SHL node's input

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We already do this for variable shifts, but we missed it for constant shifts

Fixes #69965
This commit is contained in:
Simon Pilgrim
2023-10-26 10:34:06 +01:00
parent 12dfcc0238
commit 547dc46122
2 changed files with 21 additions and 9 deletions
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11
llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
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@@ -1786,8 +1786,17 @@ bool TargetLowering::SimplifyDemandedBits(
APInt InDemandedMask = DemandedBits.lshr(ShAmt);
if (SimplifyDemandedBits(Op0, InDemandedMask, DemandedElts, Known, TLO,
Depth + 1))
Depth + 1)) {
SDNodeFlags Flags = Op.getNode()->getFlags();
if (Flags.hasNoSignedWrap() || Flags.hasNoUnsignedWrap()) {
// Disable the nsw and nuw flags. We can no longer guarantee that we
// won't wrap after simplification.
Flags.setNoSignedWrap(false);
Flags.setNoUnsignedWrap(false);
Op->setFlags(Flags);
}
return true;
}
assert(!Known.hasConflict() && "Bits known to be one AND zero?");
Known.Zero <<= ShAmt;
Known.One <<= ShAmt;

19
llvm/test/CodeGen/X86/pr69965.ll
View File

@@ -10,10 +10,12 @@ define i64 @PR69965(ptr %input_ptrs, ptr %output_ptrs) {
; X86-NEXT: movl (%eax), %eax
; X86-NEXT: movzbl (%eax), %eax
; X86-NEXT: notl %eax
; X86-NEXT: movzbl %al, %edx
; X86-NEXT: shll $8, %eax
; X86-NEXT: movl %eax, %edx
; X86-NEXT: shll $8, %edx
; X86-NEXT: movl (%ecx), %ecx
; X86-NEXT: leal (%eax,%edx,2), %eax
; X86-NEXT: addb %al, %al
; X86-NEXT: movzbl %al, %eax
; X86-NEXT: orl %edx, %eax
; X86-NEXT: orl $32768, %eax # imm = 0x8000
; X86-NEXT: movw %ax, (%ecx)
; X86-NEXT: xorl %eax, %eax
@@ -25,13 +27,14 @@ define i64 @PR69965(ptr %input_ptrs, ptr %output_ptrs) {
; X64-NEXT: movq (%rdi), %rax
; X64-NEXT: movzbl (%rax), %eax
; X64-NEXT: notl %eax
; X64-NEXT: movzbl %al, %ecx
; X64-NEXT: # kill: def $eax killed $eax def $rax
; X64-NEXT: leal (%rax,%rax), %ecx
; X64-NEXT: # kill: def $eax killed $eax killed $rax
; X64-NEXT: shll $8, %eax
; X64-NEXT: movq (%rsi), %rdx
; X64-NEXT: leal (%rax,%rcx,2), %eax
; X64-NEXT: orl $32768, %eax # imm = 0x8000
; X64-NEXT: movw %ax, (%rdx)
; X64-NEXT: movzbl %cl, %ecx
; X64-NEXT: orl %eax, %ecx
; X64-NEXT: orl $32768, %ecx # imm = 0x8000
; X64-NEXT: movw %cx, (%rdx)
; X64-NEXT: xorl %eax, %eax
; X64-NEXT: retq
entry: