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[ValueTracking] Handle not in dominating condition. #126423

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Merged
merged 1 commit into from
Feb 10, 2025
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[ValueTracking] Handle not in dominating condition. #126423

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11 changes: 11 additions & 0 deletions llvm/lib/Analysis/ValueTracking.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -801,6 +801,9 @@ static void computeKnownBitsFromCond(const Value *V, Value *Cond,

if (auto *Cmp = dyn_cast<ICmpInst>(Cond))
computeKnownBitsFromICmpCond(V, Cmp, Known, SQ, Invert);

if (Depth < MaxAnalysisRecursionDepth && match(Cond, m_Not(m_Value(A))))
computeKnownBitsFromCond(V, A, Known, Depth + 1, SQ, !Invert);
}

void llvm::computeKnownBitsFromContext(const Value *V, KnownBits &Known,
Expand Down Expand Up @@ -4934,6 +4937,11 @@ static void computeKnownFPClassFromCond(const Value *V, Value *Cond,
KnownFromContext);
return;
}
if (Depth < MaxAnalysisRecursionDepth && match(Cond, m_Not(m_Value(A)))) {
computeKnownFPClassFromCond(V, A, Depth + 1, !CondIsTrue, CxtI,
KnownFromContext);
return;
}
CmpPredicate Pred;
Value *LHS;
uint64_t ClassVal = 0;
Expand Down Expand Up @@ -10272,6 +10280,9 @@ void llvm::findValuesAffectedByCondition(
m_Value()))) {
// Handle patterns that computeKnownFPClass() support.
AddAffected(A);
} else if (!IsAssume && match(V, m_Not(m_Value(X)))) {
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Can we drop the !IsAssume here and instead drop the m_Not special case for assumes above?

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to be able to do that isEphemeralValueOf need to be updated to handle that.
example of test that will fail as the assume is optimized away.

llvm-project/llvm/test/Transforms/GVN/assume.ll

Lines 48 to 61 in 3d14000

define void @pr47496(i8 %x) {
; CHECK-LABEL: @pr47496(
; CHECK-NEXT: [[CMP:%.*]] = icmp slt i8 [[X:%.*]], 0
; CHECK-NEXT: [[XOR:%.*]] = xor i1 [[CMP]], true
; CHECK-NEXT: call void @llvm.assume(i1 [[XOR]])
; CHECK-NEXT: call void @use(i1 false)
; CHECK-NEXT: ret void
;
%cmp = icmp slt i8 %x, 0
%xor = xor i1 %cmp, true
call void @llvm.assume(i1 %xor)
call void @use(i1 %cmp)
ret void
}

Maybe all instructions with boolean results building up the condition for the assume shall be Ephemeral.

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@andjo403 andjo403 Feb 9, 2025 •
edited
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Have some follow up changes that update isEphemeralValueOf here main...andjo403:llvm-project:assumeNotCond but probably better as multiple PRs if that is something that we want

// Assume is checked here to avoid issues with ephemeral values
Worklist.push_back(X);
}
}
}
3 changes: 1 addition & 2 deletions llvm/test/Transforms/InstCombine/fpclass-from-dom-cond.ll
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Expand Up @@ -528,8 +528,7 @@ define i1 @test_inv_and(float %x, i1 %cond2) {
; CHECK-NEXT: [[AND:%.*]] = and i1 [[COND2]], [[NOT]]
; CHECK-NEXT: br i1 [[AND]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
; CHECK: if.then:
; CHECK-NEXT: [[RET1:%.*]] = fcmp oeq float [[X]], 0x7FF0000000000000
; CHECK-NEXT: ret i1 [[RET1]]
; CHECK-NEXT: ret i1 false
; CHECK: if.else:
; CHECK-NEXT: ret i1 false
;
Expand Down
3 changes: 1 addition & 2 deletions llvm/test/Transforms/InstCombine/known-bits.ll
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Expand Up @@ -2374,8 +2374,7 @@ define i8 @test_inv_cond_and(i8 %x, i1 %c) {
; CHECK-NEXT: [[COND:%.*]] = and i1 [[C:%.*]], [[NOT]]
; CHECK-NEXT: br i1 [[COND]], label [[IF:%.*]], label [[EXIT:%.*]]
; CHECK: if:
; CHECK-NEXT: [[OR1:%.*]] = or i8 [[X]], -4
; CHECK-NEXT: ret i8 [[OR1]]
; CHECK-NEXT: ret i8 -4
; CHECK: exit:
; CHECK-NEXT: [[OR2:%.*]] = or i8 [[X]], -4
; CHECK-NEXT: ret i8 [[OR2]]
Expand Down