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[ValueTracking] Handle trunc nuw in computeKnownBitsFromICmpCond #125414

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Merged
merged 3 commits into from
Feb 3, 2025
Merged

[ValueTracking] Handle trunc nuw in computeKnownBitsFromICmpCond #125414

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4405af5
[InstCombine] Add pre-commit tests. NFC.
dtcxzyw Feb 2, 2025
a02eade
[ValueTracking] Handle `trunc nuw` in `computeKnownBitsFromICmpCond`
dtcxzyw Feb 2, 2025
ae59b59
[ValueTracking] Address review comments. NFC.
dtcxzyw Feb 3, 2025
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5 changes: 4 additions & 1 deletion llvm/lib/Analysis/ValueTracking.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -776,7 +776,10 @@ static void computeKnownBitsFromICmpCond(const Value *V, ICmpInst *Cmp,
if (match(LHS, m_Trunc(m_Specific(V)))) {
KnownBits DstKnown(LHS->getType()->getScalarSizeInBits());
computeKnownBitsFromCmp(LHS, Pred, LHS, RHS, DstKnown, SQ);
Known = Known.unionWith(DstKnown.anyext(Known.getBitWidth()));
if (cast<TruncInst>(LHS)->hasNoUnsignedWrap())
Known = Known.unionWith(DstKnown.zext(Known.getBitWidth()));
else
Known = Known.unionWith(DstKnown.anyext(Known.getBitWidth()));
return;
}

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49 changes: 49 additions & 0 deletions llvm/test/Transforms/InstCombine/known-bits.ll
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Expand Up @@ -480,6 +480,55 @@ if.else:
ret i64 13
}

define i64 @test_icmp_trunc_nuw(i64 %a) {
; CHECK-LABEL: @test_icmp_trunc_nuw(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[CAST:%.*]] = trunc nuw i64 [[A:%.*]] to i32
; CHECK-NEXT: [[CMP:%.*]] = icmp sgt i32 [[CAST]], 0
; CHECK-NEXT: br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
; CHECK: if.then:
; CHECK-NEXT: ret i64 [[A]]
; CHECK: if.else:
; CHECK-NEXT: ret i64 0
;
entry:
%cast = trunc nuw i64 %a to i32
%cmp = icmp sgt i32 %cast, 0
br i1 %cmp, label %if.then, label %if.else

if.then:
%b = and i64 %a, 2147483647
ret i64 %b

if.else:
ret i64 0
}

define i64 @test_icmp_trunc_no_nuw(i64 %a) {
; CHECK-LABEL: @test_icmp_trunc_no_nuw(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[CAST:%.*]] = trunc i64 [[A:%.*]] to i32
; CHECK-NEXT: [[CMP:%.*]] = icmp sgt i32 [[CAST]], 0
; CHECK-NEXT: br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
; CHECK: if.then:
; CHECK-NEXT: [[B:%.*]] = and i64 [[A]], 2147483647
; CHECK-NEXT: ret i64 [[B]]
; CHECK: if.else:
; CHECK-NEXT: ret i64 0
;
entry:
%cast = trunc i64 %a to i32
%cmp = icmp sgt i32 %cast, 0
br i1 %cmp, label %if.then, label %if.else

if.then:
%b = and i64 %a, 2147483647
ret i64 %b

if.else:
ret i64 0
}

define i1 @test_icmp_or_distjoint(i8 %n, i1 %other) {
; CHECK-LABEL: @test_icmp_or_distjoint(
; CHECK-NEXT: entry:
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