[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 08:43:26 PDT 2024
https://github.com/dtcxzyw created https://github.com/llvm/llvm-project/pull/92773
This patch extends the transform `(icmp pred iM (shl iM %v, N), C) -> (icmp pred i(M-N) (trunc %v iM to i(M-N)), (trunc (C>>N))` to handle icmps with the flipped strictness of predicate.
See the following case:
```
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
```
Fixes the regression introduced by https://github.com/llvm/llvm-project/pull/86111#issuecomment-2098203152.
Alive2 proofs: https://alive2.llvm.org/ce/z/-sp5n3
`nuw` cannot be propagated as we always use `ashr` here. I don't see the value of fixing this (see the test `test_icmp_shl_nuw`).
>From fa36954024e7708a7d99d65fe3669bba5926175b Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Mon, 20 May 2024 23:00:01 +0800
Subject: [PATCH 1/2] [InstCombine] Add pre-commit tests. NFC.
---
llvm/test/Transforms/InstCombine/icmp.ll | 78 ++++++++++++++++++++++++
1 file changed, 78 insertions(+)
diff --git a/llvm/test/Transforms/InstCombine/icmp.ll b/llvm/test/Transforms/InstCombine/icmp.ll
index 2d786c8f48833..6e1a8c2a289f7 100644
--- a/llvm/test/Transforms/InstCombine/icmp.ll
+++ b/llvm/test/Transforms/InstCombine/icmp.ll
@@ -5198,3 +5198,81 @@ 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: [[SHL:%.*]] = shl i64 [[X:%.*]], 32
+; CHECK-NEXT: [[CMP:%.*]] = icmp ult i64 [[SHL]], 8589934593
+; 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: [[SHL:%.*]] = shl nsw i64 [[X:%.*]], 32
+; CHECK-NEXT: [[CMP:%.*]] = icmp ult i64 [[SHL]], 8589934593
+; 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: [[SHL:%.*]] = shl <2 x i64> [[X:%.*]], <i64 32, i64 32>
+; CHECK-NEXT: [[CMP:%.*]] = icmp ult <2 x i64> [[SHL]], <i64 8589934593, i64 8589934593>
+; CHECK-NEXT: ret <2 x i1> [[CMP]]
+;
+ %shl = shl <2 x i64> %x, splat(i64 32)
+ %cmp = icmp ult <2 x i64> %shl, splat(i64 8589934593)
+ ret <2 x i1> %cmp
+}
>From 91faa84c4ce2fae976e48116805cba27434db2d8 Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Mon, 20 May 2024 23:04:22 +0800
Subject: [PATCH 2/2] [InstCombine] Try the flipped strictness of predicate in
`foldICmpShlConstant`.
---
.../InstCombine/InstCombineCompares.cpp | 39 +++++++++++++++----
llvm/test/Transforms/InstCombine/icmp.ll | 11 +++---
2 files changed, 36 insertions(+), 14 deletions(-)
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 542a1c82b127a..f5952362f56bd 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -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 =
+ InstCombiner::getFlippedStrictnessPredicateAndConstant(
+ Pred, ConstantInt::get(ShType->getContext(), C))) {
+ ICmpInst::Predicate NewPred = FlippedStrictness->first;
+ const APInt &NewC =
+ cast<ConstantInt>(FlippedStrictness->second)->getValue();
+ if (Instruction *Res = FoldICmpShlToICmpTrunc(NewPred, NewC))
+ return Res;
+ }
}
return nullptr;
diff --git a/llvm/test/Transforms/InstCombine/icmp.ll b/llvm/test/Transforms/InstCombine/icmp.ll
index 6e1a8c2a289f7..319e13235ccd6 100644
--- a/llvm/test/Transforms/InstCombine/icmp.ll
+++ b/llvm/test/Transforms/InstCombine/icmp.ll
@@ -5201,8 +5201,8 @@ define i1 @icmp_freeze_sext(i16 %x, i16 %y) {
define i1 @test_icmp_shl(i64 %x) {
; CHECK-LABEL: @test_icmp_shl(
-; CHECK-NEXT: [[SHL:%.*]] = shl i64 [[X:%.*]], 32
-; CHECK-NEXT: [[CMP:%.*]] = icmp ult i64 [[SHL]], 8589934593
+; 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
@@ -5257,8 +5257,7 @@ define i1 @test_icmp_shl_nuw(i64 %x) {
define i1 @test_icmp_shl_nsw(i64 %x) {
; CHECK-LABEL: @test_icmp_shl_nsw(
-; CHECK-NEXT: [[SHL:%.*]] = shl nsw i64 [[X:%.*]], 32
-; CHECK-NEXT: [[CMP:%.*]] = icmp ult i64 [[SHL]], 8589934593
+; CHECK-NEXT: [[CMP:%.*]] = icmp ult i64 [[X:%.*]], 3
; CHECK-NEXT: ret i1 [[CMP]]
;
%shl = shl nsw i64 %x, 32
@@ -5268,8 +5267,8 @@ define i1 @test_icmp_shl_nsw(i64 %x) {
define <2 x i1> @test_icmp_shl_vec(<2 x i64> %x) {
; CHECK-LABEL: @test_icmp_shl_vec(
-; CHECK-NEXT: [[SHL:%.*]] = shl <2 x i64> [[X:%.*]], <i64 32, i64 32>
-; CHECK-NEXT: [[CMP:%.*]] = icmp ult <2 x i64> [[SHL]], <i64 8589934593, i64 8589934593>
+; 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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