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[InstCombine] Try the flipped strictness of predicate in foldICmpShlConstant #92773

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Merged
merged 4 commits into from
May 28, 2024
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[InstCombine] Try the flipped strictness of predicate in foldICmpShlConstant #92773

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fa36954
[InstCombine] Add pre-commit tests. NFC.
dtcxzyw May 20, 2024
91faa84
[InstCombine] Try the flipped strictness of predicate in `foldICmpShl…
dtcxzyw May 20, 2024
bba9b38
[InstCombine] Address review comments.
dtcxzyw May 20, 2024
c28db82
[InstCombine] Simplify code. NFC.
dtcxzyw May 20, 2024
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36 changes: 28 additions & 8 deletions llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2414,14 +2414,34 @@ Instruction *InstCombinerImpl::foldICmpShlConstant(ICmpInst &Cmp,
// free on the target. It has the additional benefit of comparing to a
// smaller constant that may be more target-friendly.
unsigned Amt = ShiftAmt->getLimitedValue(TypeBits - 1);
if (Shl->hasOneUse() && Amt != 0 && C.countr_zero() >= Amt &&
DL.isLegalInteger(TypeBits - Amt)) {
Type *TruncTy = IntegerType::get(Cmp.getContext(), TypeBits - Amt);
if (auto *ShVTy = dyn_cast<VectorType>(ShType))
TruncTy = VectorType::get(TruncTy, ShVTy->getElementCount());
Constant *NewC =
ConstantInt::get(TruncTy, C.ashr(*ShiftAmt).trunc(TypeBits - Amt));
return new ICmpInst(Pred, Builder.CreateTrunc(X, TruncTy), NewC);
if (Shl->hasOneUse() && Amt != 0 &&
shouldChangeType(ShType->getScalarSizeInBits(), TypeBits - Amt)) {
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To account for Vec types should construct ShType->getWithNewBitWidth(TypeBits - Amt) and use that + ShType for this check.

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#92773 (comment)

It breaks some vec tests.

ICmpInst::Predicate CmpPred = Pred;
APInt RHSC = C;

if (RHSC.countr_zero() < Amt && ICmpInst::isStrictPredicate(CmpPred)) {
// Try the flipped strictness predicate.
// e.g.:
// icmp ult i64 (shl X, 32), 8589934593 ->
// icmp ule i64 (shl X, 32), 8589934592 ->
// icmp ule i32 (trunc X, i32), 2 ->
// icmp ult i32 (trunc X, i32), 3
if (auto FlippedStrictness =
InstCombiner::getFlippedStrictnessPredicateAndConstant(
Pred, ConstantInt::get(ShType->getContext(), C))) {
CmpPred = FlippedStrictness->first;
RHSC = cast<ConstantInt>(FlippedStrictness->second)->getValue();
}
}

if (RHSC.countr_zero() >= Amt) {
Type *TruncTy = ShType->getWithNewBitWidth(TypeBits - Amt);
Constant *NewC =
ConstantInt::get(TruncTy, RHSC.ashr(*ShiftAmt).trunc(TypeBits - Amt));
return new ICmpInst(
CmpPred, Builder.CreateTrunc(X, TruncTy, "", Shl->hasNoSignedWrap()),
NewC);
}
}

return nullptr;
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97 changes: 97 additions & 0 deletions llvm/test/Transforms/InstCombine/icmp.ll
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Expand Up @@ -5198,3 +5198,100 @@ define i1 @icmp_freeze_sext(i16 %x, i16 %y) {
%cmp2 = icmp uge i16 %ext.fr, %y
ret i1 %cmp2
}

define i1 @test_icmp_shl(i64 %x) {
; CHECK-LABEL: @test_icmp_shl(
; CHECK-NEXT: [[TMP1:%.*]] = trunc i64 [[X:%.*]] to i32
; CHECK-NEXT: [[CMP:%.*]] = icmp ult i32 [[TMP1]], 3
; CHECK-NEXT: ret i1 [[CMP]]
;
%shl = shl i64 %x, 32
%cmp = icmp ult i64 %shl, 8589934593
ret i1 %cmp
}

define i1 @test_icmp_shl_multiuse(i64 %x) {
; CHECK-LABEL: @test_icmp_shl_multiuse(
; CHECK-NEXT: [[SHL:%.*]] = shl i64 [[X:%.*]], 32
; CHECK-NEXT: call void @use_i64(i64 [[SHL]])
; CHECK-NEXT: [[CMP:%.*]] = icmp ult i64 [[SHL]], 8589934593
; CHECK-NEXT: ret i1 [[CMP]]
;
%shl = shl i64 %x, 32
call void @use_i64(i64 %shl)
%cmp = icmp ult i64 %shl, 8589934593
ret i1 %cmp
}

define i1 @test_icmp_shl_illegal_length(i64 %x) {
; CHECK-LABEL: @test_icmp_shl_illegal_length(
; CHECK-NEXT: [[SHL:%.*]] = shl i64 [[X:%.*]], 31
; CHECK-NEXT: [[CMP:%.*]] = icmp ult i64 [[SHL]], 8589934593
; CHECK-NEXT: ret i1 [[CMP]]
;
%shl = shl i64 %x, 31
%cmp = icmp ult i64 %shl, 8589934593
ret i1 %cmp
}

define i1 @test_icmp_shl_invalid_rhsc(i64 %x) {
; CHECK-LABEL: @test_icmp_shl_invalid_rhsc(
; CHECK-NEXT: [[SHL:%.*]] = shl i64 [[X:%.*]], 32
; CHECK-NEXT: [[CMP:%.*]] = icmp ult i64 [[SHL]], 8589934595
; CHECK-NEXT: ret i1 [[CMP]]
;
%shl = shl i64 %x, 32
%cmp = icmp ult i64 %shl, 8589934595
ret i1 %cmp
}

define i1 @test_icmp_shl_nuw(i64 %x) {
; CHECK-LABEL: @test_icmp_shl_nuw(
; CHECK-NEXT: [[CMP:%.*]] = icmp ult i64 [[X:%.*]], 3
; CHECK-NEXT: ret i1 [[CMP]]
;
%shl = shl nuw i64 %x, 32
%cmp = icmp ult i64 %shl, 8589934593
ret i1 %cmp
}

define i1 @test_icmp_shl_nsw(i64 %x) {
; CHECK-LABEL: @test_icmp_shl_nsw(
; CHECK-NEXT: [[CMP:%.*]] = icmp ult i64 [[X:%.*]], 3
; CHECK-NEXT: ret i1 [[CMP]]
;
%shl = shl nsw i64 %x, 32
%cmp = icmp ult i64 %shl, 8589934593
ret i1 %cmp
}

define <2 x i1> @test_icmp_shl_vec(<2 x i64> %x) {
; CHECK-LABEL: @test_icmp_shl_vec(
; CHECK-NEXT: [[TMP1:%.*]] = trunc <2 x i64> [[X:%.*]] to <2 x i32>
; CHECK-NEXT: [[CMP:%.*]] = icmp ult <2 x i32> [[TMP1]], <i32 3, i32 3>
; CHECK-NEXT: ret <2 x i1> [[CMP]]
;
%shl = shl <2 x i64> %x, splat(i64 32)
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didn't know about the splat syntax, thats nice :)

%cmp = icmp ult <2 x i64> %shl, splat(i64 8589934593)
ret <2 x i1> %cmp
}

define i1 @test_icmp_shl_eq(i64 %x) {
; CHECK-LABEL: @test_icmp_shl_eq(
; CHECK-NEXT: ret i1 false
;
%shl = shl i64 %x, 32
%cmp = icmp eq i64 %shl, 8589934593
ret i1 %cmp
}

define i1 @test_icmp_shl_sgt(i64 %x) {
; CHECK-LABEL: @test_icmp_shl_sgt(
; CHECK-NEXT: [[TMP1:%.*]] = trunc i64 [[X:%.*]] to i32
; CHECK-NEXT: [[CMP:%.*]] = icmp sgt i32 [[TMP1]], 1
; CHECK-NEXT: ret i1 [[CMP]]
;
%shl = shl i64 %x, 32
%cmp = icmp sgt i64 %shl, 8589934591
ret i1 %cmp
}
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