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[InstSimplify] Make sure the simplified value doesn't generate poison in threadBinOpOverSelect #87075

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Apr 11, 2024
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[InstSimplify] Make sure the simplified value doesn't generate poison in threadBinOpOverSelect #87075

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b035913
[InstSimplify] Add pre-commit tests. NFC.
dtcxzyw Mar 29, 2024
4ca1c82
[InstSimplify] Make sure the simplified value doesn't generate poison…
dtcxzyw Mar 29, 2024
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3 changes: 2 additions & 1 deletion llvm/lib/Analysis/InstructionSimplify.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -440,7 +440,8 @@ static Value *threadBinOpOverSelect(Instruction::BinaryOps Opcode, Value *LHS,
// Check that the simplified value has the form "X op Y" where "op" is the
// same as the original operation.
Instruction *Simplified = dyn_cast<Instruction>(FV ? FV : TV);
if (Simplified && Simplified->getOpcode() == unsigned(Opcode)) {
if (Simplified && Simplified->getOpcode() == unsigned(Opcode) &&
!Simplified->hasPoisonGeneratingFlags()) {
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Shouldn't isSafeToSpeculativelyExecute suffice here?

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isSafeToSpeculativelyExecute only cares about immediate UB instead of poison.

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why is the fix to prohibit any poison flag and not to just drop the poison generating flag?

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IIRC modifying an instruction is not allowed in InstSimplify :(

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oh yeah xD

Maybe just move this to InstCombine? Or put equivelent code that drops poison generating flags there?

// The value that didn't simplify is "UnsimplifiedLHS op UnsimplifiedRHS".
// We already know that "op" is the same as for the simplified value. See
// if the operands match too. If so, return the simplified value.
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42 changes: 42 additions & 0 deletions llvm/test/Transforms/InstSimplify/pr87042.ll
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@@ -0,0 +1,42 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4
; RUN: opt < %s -passes=instsimplify -S | FileCheck %s

; %or2 cannot be folded into %or1 because %or1 has disjoint.
; TODO: Can we move the logic into InstCombine and drop the disjoint flag?
define i64 @test(i1 %cond, i64 %x) {
; CHECK-LABEL: define i64 @test(
; CHECK-SAME: i1 [[COND:%.*]], i64 [[X:%.*]]) {
; CHECK-NEXT: [[OR1:%.*]] = or disjoint i64 [[X]], 7
; CHECK-NEXT: [[SEL1:%.*]] = select i1 [[COND]], i64 [[OR1]], i64 [[X]]
; CHECK-NEXT: [[OR2:%.*]] = or i64 [[SEL1]], 7
; CHECK-NEXT: ret i64 [[OR2]]
;
%or1 = or disjoint i64 %x, 7
%sel1 = select i1 %cond, i64 %or1, i64 %x
%or2 = or i64 %sel1, 7
ret i64 %or2
}

define i64 @pr87042(i64 %x) {
; CHECK-LABEL: define i64 @pr87042(
; CHECK-SAME: i64 [[X:%.*]]) {
; CHECK-NEXT: [[AND1:%.*]] = and i64 [[X]], 65535
; CHECK-NEXT: [[CMP1:%.*]] = icmp eq i64 [[AND1]], 0
; CHECK-NEXT: [[OR1:%.*]] = or disjoint i64 [[X]], 7
; CHECK-NEXT: [[SEL1:%.*]] = select i1 [[CMP1]], i64 [[OR1]], i64 [[X]]
; CHECK-NEXT: [[AND2:%.*]] = and i64 [[SEL1]], 16776960
; CHECK-NEXT: [[CMP2:%.*]] = icmp eq i64 [[AND2]], 0
; CHECK-NEXT: [[OR2:%.*]] = or i64 [[SEL1]], 7
; CHECK-NEXT: [[SEL2:%.*]] = select i1 [[CMP2]], i64 [[OR2]], i64 [[SEL1]]
; CHECK-NEXT: ret i64 [[SEL2]]
;
%and1 = and i64 %x, 65535
%cmp1 = icmp eq i64 %and1, 0
%or1 = or disjoint i64 %x, 7
%sel1 = select i1 %cmp1, i64 %or1, i64 %x
%and2 = and i64 %sel1, 16776960
%cmp2 = icmp eq i64 %and2, 0
%or2 = or i64 %sel1, 7
%sel2 = select i1 %cmp2, i64 %or2, i64 %sel1
ret i64 %sel2
}
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