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[ValueTracking] Handle trunc to i1 as condition in dominating condition. #126414

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Merged
merged 1 commit into from
Feb 11, 2025
Merged

[ValueTracking] Handle trunc to i1 as condition in dominating condition. #126414

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24 changes: 23 additions & 1 deletion llvm/lib/Analysis/ValueTracking.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -797,10 +797,28 @@ static void computeKnownBitsFromCond(const Value *V, Value *Cond,
else
Known2 = Known2.intersectWith(Known3);
Known = Known.unionWith(Known2);
return;
}

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

if (match(Cond, m_Trunc(m_Specific(V)))) {
KnownBits DstKnown(1);
if (Invert) {
DstKnown.setAllZero();
} else {
DstKnown.setAllOnes();
}
if (cast<TruncInst>(Cond)->hasNoUnsignedWrap()) {
Known = Known.unionWith(DstKnown.zext(Known.getBitWidth()));
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you can sext if you have trunc nsw

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avoided sext as it was not handled i #125414 seems like it is uncommon to have sext for trunc to i1 only found 3 in llvm-opt-benchmark

return;
}
Known = Known.unionWith(DstKnown.anyext(Known.getBitWidth()));
return;
}

if (Depth < MaxAnalysisRecursionDepth && match(Cond, m_Not(m_Value(A))))
computeKnownBitsFromCond(V, A, Known, Depth + 1, SQ, !Invert);
Expand Down Expand Up @@ -10280,6 +10298,10 @@ void llvm::findValuesAffectedByCondition(
m_Value()))) {
// Handle patterns that computeKnownFPClass() support.
AddAffected(A);
} else if (!IsAssume && match(V, m_Trunc(m_Value(X)))) {
// Assume is checked here as X is already added above for assumes in
// addValueAffectedByCondition
AddAffected(X);
} else if (!IsAssume && match(V, m_Not(m_Value(X)))) {
// Assume is checked here to avoid issues with ephemeral values
Worklist.push_back(X);
Expand Down
36 changes: 12 additions & 24 deletions llvm/test/Transforms/InstCombine/known-bits.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -2167,11 +2167,9 @@ define i8 @test_trunc_and_1(i8 %a) {
; CHECK-NEXT: [[CAST:%.*]] = trunc i8 [[A:%.*]] to i1
; CHECK-NEXT: br i1 [[CAST]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
; CHECK: if.then:
; CHECK-NEXT: [[B:%.*]] = and i8 [[A]], 1
; CHECK-NEXT: ret i8 [[B]]
; CHECK-NEXT: ret i8 1
; CHECK: if.else:
; CHECK-NEXT: [[C:%.*]] = and i8 [[A]], 1
; CHECK-NEXT: ret i8 [[C]]
; CHECK-NEXT: ret i8 0
;
entry:
%cast = trunc i8 %a to i1
Expand All @@ -2192,11 +2190,9 @@ define i8 @test_not_trunc_and_1(i8 %a) {
; CHECK-NEXT: [[CAST:%.*]] = trunc i8 [[A:%.*]] to i1
; CHECK-NEXT: br i1 [[CAST]], label [[IF_ELSE:%.*]], label [[IF_THEN:%.*]]
; CHECK: if.then:
; CHECK-NEXT: [[B:%.*]] = and i8 [[A]], 1
; CHECK-NEXT: ret i8 [[B]]
; CHECK-NEXT: ret i8 0
; CHECK: if.else:
; CHECK-NEXT: [[C:%.*]] = and i8 [[A]], 1
; CHECK-NEXT: ret i8 [[C]]
; CHECK-NEXT: ret i8 1
;
entry:
%cast = trunc i8 %a to i1
Expand Down Expand Up @@ -2243,11 +2239,9 @@ define i8 @test_trunc_nuw_and_1(i8 %a) {
; CHECK-NEXT: [[CAST:%.*]] = trunc nuw i8 [[A:%.*]] to i1
; CHECK-NEXT: br i1 [[CAST]], label [[IF_ELSE:%.*]], label [[IF_THEN:%.*]]
; CHECK: if.then:
; CHECK-NEXT: [[B:%.*]] = and i8 [[A]], 1
; CHECK-NEXT: ret i8 [[B]]
; CHECK-NEXT: ret i8 0
; CHECK: if.else:
; CHECK-NEXT: [[C:%.*]] = and i8 [[A]], 1
; CHECK-NEXT: ret i8 [[C]]
; CHECK-NEXT: ret i8 1
;
entry:
%cast = trunc nuw i8 %a to i1
Expand All @@ -2268,11 +2262,9 @@ define i8 @test_trunc_nuw_or_2(i8 %a) {
; CHECK-NEXT: [[CAST:%.*]] = trunc nuw i8 [[A:%.*]] to i1
; CHECK-NEXT: br i1 [[CAST]], label [[IF_ELSE:%.*]], label [[IF_THEN:%.*]]
; CHECK: if.then:
; CHECK-NEXT: [[B:%.*]] = or i8 [[A]], 2
; CHECK-NEXT: ret i8 [[B]]
; CHECK-NEXT: ret i8 2
; CHECK: if.else:
; CHECK-NEXT: [[C:%.*]] = or i8 [[A]], 2
; CHECK-NEXT: ret i8 [[C]]
; CHECK-NEXT: ret i8 3
;
entry:
%cast = trunc nuw i8 %a to i1
Expand All @@ -2293,11 +2285,9 @@ define i8 @test_not_trunc_nuw_and_1(i8 %a) {
; CHECK-NEXT: [[CAST:%.*]] = trunc nuw i8 [[A:%.*]] to i1
; CHECK-NEXT: br i1 [[CAST]], label [[IF_ELSE:%.*]], label [[IF_THEN:%.*]]
; CHECK: if.then:
; CHECK-NEXT: [[B:%.*]] = and i8 [[A]], 1
; CHECK-NEXT: ret i8 [[B]]
; CHECK-NEXT: ret i8 0
; CHECK: if.else:
; CHECK-NEXT: [[C:%.*]] = and i8 [[A]], 1
; CHECK-NEXT: ret i8 [[C]]
; CHECK-NEXT: ret i8 1
;
entry:
%cast = trunc nuw i8 %a to i1
Expand All @@ -2319,8 +2309,7 @@ define i8 @test_trunc_cond_and(i8 %x, i1 %c) {
; CHECK-NEXT: [[COND:%.*]] = and i1 [[C:%.*]], [[CMP]]
; CHECK-NEXT: br i1 [[COND]], label [[IF:%.*]], label [[EXIT:%.*]]
; CHECK: if:
; CHECK-NEXT: [[OR1:%.*]] = or i8 [[X]], -2
; CHECK-NEXT: ret i8 [[OR1]]
; CHECK-NEXT: ret i8 -1
; CHECK: exit:
; CHECK-NEXT: [[OR2:%.*]] = or i8 [[X]], -2
; CHECK-NEXT: ret i8 [[OR2]]
Expand All @@ -2345,8 +2334,7 @@ define i8 @test_not_trunc_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]], -2
; CHECK-NEXT: ret i8 [[OR1]]
; CHECK-NEXT: ret i8 -2
; CHECK: exit:
; CHECK-NEXT: [[OR2:%.*]] = or i8 [[X]], -2
; CHECK-NEXT: ret i8 [[OR2]]
Expand Down