[llvm] [InstCombine] Use known bits to simplify mask in foldSelectICmpAnd (PR #128741)
Julian Nagele via llvm-commits
llvm-commits at lists.llvm.org
Thu Mar 13 10:52:24 PDT 2025
https://github.com/juliannagele updated https://github.com/llvm/llvm-project/pull/128741
>From 7f78ed9ad91ae71c78e50ef0c37b1ce44be16d77 Mon Sep 17 00:00:00 2001
From: Julian Nagele <j.nagele at apple.com>
Date: Tue, 25 Feb 2025 15:44:19 +0000
Subject: [PATCH 1/4] [InstCombine] Add test showing bittest which uses range
attribute
---
llvm/test/Transforms/InstCombine/select-icmp-and.ll | 11 +++++++++++
1 file changed, 11 insertions(+)
diff --git a/llvm/test/Transforms/InstCombine/select-icmp-and.ll b/llvm/test/Transforms/InstCombine/select-icmp-and.ll
index 16fb3f34047ee..09a4b0dc64699 100644
--- a/llvm/test/Transforms/InstCombine/select-icmp-and.ll
+++ b/llvm/test/Transforms/InstCombine/select-icmp-and.ll
@@ -912,3 +912,14 @@ define i16 @select_trunc_nuw_bittest_or(i8 %x) {
%res = or i16 4, %select
ret i16 %res
}
+
+define i16 @select_icmp_bittest_range(i16 range (i16 0, 512) %a) {
+; CHECK-LABEL: @select_icmp_bittest_range(
+; CHECK-NEXT: [[CMP:%.*]] = icmp samesign ult i16 [[A:%.*]], 256
+; CHECK-NEXT: [[RES:%.*]] = select i1 [[CMP]], i16 0, i16 256
+; CHECK-NEXT: ret i16 [[RES]]
+;
+ %cmp = icmp ult i16 %a, 256
+ %res = select i1 %cmp, i16 0, i16 256
+ ret i16 %res
+}
>From ffd72987fb6c05cb387ac99e17b05decdcfc2926 Mon Sep 17 00:00:00 2001
From: Julian Nagele <j.nagele at apple.com>
Date: Tue, 25 Feb 2025 15:52:21 +0000
Subject: [PATCH 2/4] [InstCombine] Use known bits to simplify mask in
foldSelectICmpAnd
---
.../Transforms/InstCombine/InstCombineSelect.cpp | 13 ++++++++-----
llvm/test/Transforms/InstCombine/select-icmp-and.ll | 3 +--
2 files changed, 9 insertions(+), 7 deletions(-)
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index dca969e160bb7..dc317da97e13c 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -120,7 +120,8 @@ static Instruction *foldSelectBinOpIdentity(SelectInst &Sel,
/// With some variations depending if FC is larger than TC, or the shift
/// isn't needed, or the bit widths don't match.
static Value *foldSelectICmpAnd(SelectInst &Sel, ICmpInst *Cmp,
- InstCombiner::BuilderTy &Builder) {
+ InstCombiner::BuilderTy &Builder,
+ SimplifyQuery &SQ) {
const APInt *SelTC, *SelFC;
if (!match(Sel.getTrueValue(), m_APInt(SelTC)) ||
!match(Sel.getFalseValue(), m_APInt(SelFC)))
@@ -148,11 +149,13 @@ static Value *foldSelectICmpAnd(SelectInst &Sel, ICmpInst *Cmp,
} else if (auto Res = decomposeBitTestICmp(Cmp->getOperand(0),
Cmp->getOperand(1), Pred)) {
assert(ICmpInst::isEquality(Res->Pred) && "Not equality test?");
- if (!Res->Mask.isPowerOf2())
+ AndMask = Res->Mask;
+ V = Res->X;
+ KnownBits Known = computeKnownBits(V, 0, SQ.getWithInstruction(Cmp));
+ AndMask &= Known.getMaxValue();
+ if (!AndMask.isPowerOf2())
return nullptr;
- V = Res->X;
- AndMask = Res->Mask;
Pred = Res->Pred;
CreateAnd = true;
} else {
@@ -1957,7 +1960,7 @@ Instruction *InstCombinerImpl::foldSelectInstWithICmp(SelectInst &SI,
tryToReuseConstantFromSelectInComparison(SI, *ICI, *this))
return NewSel;
- if (Value *V = foldSelectICmpAnd(SI, ICI, Builder))
+ if (Value *V = foldSelectICmpAnd(SI, ICI, Builder, SQ))
return replaceInstUsesWith(SI, V);
// NOTE: if we wanted to, this is where to detect integer MIN/MAX
diff --git a/llvm/test/Transforms/InstCombine/select-icmp-and.ll b/llvm/test/Transforms/InstCombine/select-icmp-and.ll
index 09a4b0dc64699..c84e925658046 100644
--- a/llvm/test/Transforms/InstCombine/select-icmp-and.ll
+++ b/llvm/test/Transforms/InstCombine/select-icmp-and.ll
@@ -915,8 +915,7 @@ define i16 @select_trunc_nuw_bittest_or(i8 %x) {
define i16 @select_icmp_bittest_range(i16 range (i16 0, 512) %a) {
; CHECK-LABEL: @select_icmp_bittest_range(
-; CHECK-NEXT: [[CMP:%.*]] = icmp samesign ult i16 [[A:%.*]], 256
-; CHECK-NEXT: [[RES:%.*]] = select i1 [[CMP]], i16 0, i16 256
+; CHECK-NEXT: [[RES:%.*]] = and i16 [[A:%.*]], 256
; CHECK-NEXT: ret i16 [[RES]]
;
%cmp = icmp ult i16 %a, 256
>From 17c8b668073d874f45d5b47ba011e84ed2e35c55 Mon Sep 17 00:00:00 2001
From: Julian Nagele <j.nagele at apple.com>
Date: Fri, 7 Mar 2025 11:19:38 +0000
Subject: [PATCH 3/4] fixup! [InstCombine] Use known bits to simplify mask in
foldSelectICmpAnd
---
llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index dc317da97e13c..4346f82fa5da9 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -121,7 +121,7 @@ static Instruction *foldSelectBinOpIdentity(SelectInst &Sel,
/// isn't needed, or the bit widths don't match.
static Value *foldSelectICmpAnd(SelectInst &Sel, ICmpInst *Cmp,
InstCombiner::BuilderTy &Builder,
- SimplifyQuery &SQ) {
+ const SimplifyQuery &SQ) {
const APInt *SelTC, *SelFC;
if (!match(Sel.getTrueValue(), m_APInt(SelTC)) ||
!match(Sel.getFalseValue(), m_APInt(SelFC)))
@@ -151,7 +151,8 @@ static Value *foldSelectICmpAnd(SelectInst &Sel, ICmpInst *Cmp,
assert(ICmpInst::isEquality(Res->Pred) && "Not equality test?");
AndMask = Res->Mask;
V = Res->X;
- KnownBits Known = computeKnownBits(V, 0, SQ.getWithInstruction(Cmp));
+ KnownBits Known =
+ computeKnownBits(V, /*Depth=*/0, SQ.getWithInstruction(&Sel));
AndMask &= Known.getMaxValue();
if (!AndMask.isPowerOf2())
return nullptr;
>From 036445d82fe8896d1d02f370873c683b9c34be4b Mon Sep 17 00:00:00 2001
From: Julian Nagele <j.nagele at apple.com>
Date: Thu, 13 Mar 2025 17:51:49 +0000
Subject: [PATCH 4/4] fixup! [InstCombine] Use known bits to simplify mask in
foldSelectICmpAnd
---
.../Transforms/InstCombine/select-icmp-and.ll | 22 +++++++++++++++++++
1 file changed, 22 insertions(+)
diff --git a/llvm/test/Transforms/InstCombine/select-icmp-and.ll b/llvm/test/Transforms/InstCombine/select-icmp-and.ll
index c84e925658046..8b61b55a62712 100644
--- a/llvm/test/Transforms/InstCombine/select-icmp-and.ll
+++ b/llvm/test/Transforms/InstCombine/select-icmp-and.ll
@@ -922,3 +922,25 @@ define i16 @select_icmp_bittest_range(i16 range (i16 0, 512) %a) {
%res = select i1 %cmp, i16 0, i16 256
ret i16 %res
}
+
+define i16 @select_icmp_bittest_range_negative_test(i16 range (i16 0, 513) %a) {
+; CHECK-LABEL: @select_icmp_bittest_range_negative_test(
+; CHECK-NEXT: [[CMP:%.*]] = icmp samesign ult i16 [[A:%.*]], 256
+; CHECK-NEXT: [[RES:%.*]] = select i1 [[CMP]], i16 0, i16 256
+; CHECK-NEXT: ret i16 [[RES]]
+;
+ %cmp = icmp ult i16 %a, 256
+ %res = select i1 %cmp, i16 0, i16 256
+ ret i16 %res
+}
+
+define i16 @select_icmp_bittest_range_negative_test2(i16 range (i16 0, 512) %a) {
+; CHECK-LABEL: @select_icmp_bittest_range_negative_test2(
+; CHECK-NEXT: [[CMP:%.*]] = icmp samesign ult i16 [[A:%.*]], 255
+; CHECK-NEXT: [[RES:%.*]] = select i1 [[CMP]], i16 0, i16 255
+; CHECK-NEXT: ret i16 [[RES]]
+;
+ %cmp = icmp ult i16 %a, 255
+ %res = select i1 %cmp, i16 0, i16 255
+ ret i16 %res
+}
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