[llvm] [InstCombine] Try the flipped strictness of predicate in `foldICmpShlConstant` (PR #92773)
Yingwei Zheng via llvm-commits
llvm-commits at lists.llvm.org
Mon May 20 09:41:11 PDT 2024
================
@@ -2414,14 +2414,37 @@ 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 && DL.isLegalInteger(TypeBits - Amt)) {
+ auto FoldICmpShlToICmpTrunc = [&](ICmpInst::Predicate Pred,
+ const APInt &C) -> Instruction * {
+ if (C.countr_zero() < Amt)
+ return nullptr;
+ Type *TruncTy = ShType->getWithNewBitWidth(TypeBits - Amt);
+ Constant *NewC =
+ ConstantInt::get(TruncTy, C.ashr(*ShiftAmt).trunc(TypeBits - Amt));
+ return new ICmpInst(
+ Pred, Builder.CreateTrunc(X, TruncTy, "", Shl->hasNoSignedWrap()),
+ NewC);
+ };
+
+ if (Instruction *Res = FoldICmpShlToICmpTrunc(Pred, C))
+ return Res;
+
+ // 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 =
----------------
dtcxzyw wrote:
InstCombine calls `canonicalizeCmpWithConstant` before `foldICmpWithConstant`. So the pred should be strict.
BTW I forget to exclude `eq/ne` here :( It may cause an assertion failure.
https://github.com/llvm/llvm-project/pull/92773
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