[InstCombine] Fold (add (add A, 1), (sext (icmp ne A, 0))) to call umax(A, 1) #122491

Ruhung · 2025-01-10T16:38:38Z

Transform (add (add A, 1), (sext (icmp ne A, 0))) into call umax(A, 1).
Fixes #121853
Alive2 : https://alive2.llvm.org/ce/z/TweTan

github-actions · 2025-01-10T16:38:57Z

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llvmbot · 2025-01-10T16:39:33Z

@llvm/pr-subscribers-llvm-transforms

Author: None (Ruhung)

Changes

Transform (add (add A, 1), (sext (icmp ne A, 0))) into call umax(A, 1).
Fixes #121853
Alive2 : https://alive2.llvm.org/ce/z/TweTan

Full diff: https://github.com/llvm/llvm-project/pull/122491.diff

2 Files Affected:

(modified) llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp (+9)
(added) llvm/test/Transforms/InstCombine/add_sext_icmp.ll (+141)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index 73876d00e73a7c..83e1d3bdf9aeda 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1775,6 +1775,15 @@ Instruction *InstCombinerImpl::visitAdd(BinaryOperator &I) {
     }
   }
 
+  // (add (add A, 1), (sext (icmp ne A, 0))) => call umax(A, 1)
+  if (match(LHS, m_OneUse(m_Add(m_Value(A), m_One()))) &&
+      match(RHS, m_OneUse(m_SExt(m_OneUse(m_SpecificICmp(
+        ICmpInst::ICMP_NE, m_Deferred(A), m_ZeroInt())))))) {
+    Value *OneConst = ConstantInt::get(A->getType(), 1);
+    Value *UMax = Builder.CreateIntrinsic(Intrinsic::umax, A->getType(), {A, OneConst});
+    return replaceInstUsesWith(I, UMax);
+  }
+
   if (Instruction *Ashr = foldAddToAshr(I))
     return Ashr;
 
diff --git a/llvm/test/Transforms/InstCombine/add_sext_icmp.ll b/llvm/test/Transforms/InstCombine/add_sext_icmp.ll
new file mode 100644
index 00000000000000..f8bd106964ae44
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/add_sext_icmp.ll
@@ -0,0 +1,141 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -S -passes=instcombine < %s | FileCheck %s
+
+; The pattern:
+;   add(add A, 1), (sext(icmp ne A, 0))
+; is transformed into:
+;   umax(A, 1)
+
+define i32 @add_sext_icmp(i32 %A) {
+; CHECK-LABEL: define i32 @add_sext_icmp(
+; CHECK-SAME: i32 [[A:%.*]]) {
+; CHECK-NEXT:    [[ADD2:%.*]] = call i32 @llvm.umax.i32(i32 [[A]], i32 1)
+; CHECK-NEXT:    ret i32 [[ADD2]]
+;
+  %add1 = add i32 %A, 1
+  %icmp = icmp ne i32 %A, 0
+  %sext = sext i1 %icmp to i32
+  %add2 = add i32 %add1, %sext
+  ret i32 %add2
+}
+
+define i32 @add_sext_icmp_commutative(i32 %A) {
+; CHECK-LABEL: define i32 @add_sext_icmp_commutative(
+; CHECK-SAME: i32 [[A:%.*]]) {
+; CHECK-NEXT:    [[ADD2:%.*]] = call i32 @llvm.umax.i32(i32 [[A]], i32 1)
+; CHECK-NEXT:    ret i32 [[ADD2]]
+;
+  %add1 = add i32 %A, 1
+  %icmp = icmp ne i32 %A, 0
+  %sext = sext i1 %icmp to i32
+  %add2 = add i32 %sext, %add1
+  ret i32 %add2
+}
+
+; Negative test
+
+define i32 @add_sext_icmp_negative_constant(i32 %A) {
+; CHECK-LABEL: define i32 @add_sext_icmp_negative_constant(
+; CHECK-SAME: i32 [[A:%.*]]) {
+; CHECK-NEXT:    [[ADD1:%.*]] = add i32 [[A]], 2
+; CHECK-NEXT:    [[ICMP:%.*]] = icmp ne i32 [[A]], 0
+; CHECK-NEXT:    [[SEXT:%.*]] = sext i1 [[ICMP]] to i32
+; CHECK-NEXT:    [[ADD2:%.*]] = add i32 [[ADD1]], [[SEXT]]
+; CHECK-NEXT:    ret i32 [[ADD2]]
+;
+  %add1 = add i32 %A, 2
+  %icmp = icmp ne i32 %A, 0
+  %sext = sext i1 %icmp to i32
+  %add2 = add i32 %add1, %sext
+  ret i32 %add2
+}
+
+define i32 @add_sext_icmp_negative_pred(i32 %A) {
+; CHECK-LABEL: define i32 @add_sext_icmp_negative_pred(
+; CHECK-SAME: i32 [[A:%.*]]) {
+; CHECK-NEXT:    [[ADD1:%.*]] = add i32 [[A]], 1
+; CHECK-NEXT:    [[ICMP:%.*]] = icmp eq i32 [[A]], 0
+; CHECK-NEXT:    [[SEXT:%.*]] = sext i1 [[ICMP]] to i32
+; CHECK-NEXT:    [[ADD2:%.*]] = add i32 [[ADD1]], [[SEXT]]
+; CHECK-NEXT:    ret i32 [[ADD2]]
+;
+  %add1 = add i32 %A, 1
+  %icmp = icmp eq i32 %A, 0
+  %sext = sext i1 %icmp to i32
+  %add2 = add i32 %add1, %sext
+  ret i32 %add2
+}
+
+; multi-use test
+
+define i32 @add_sext_icmp_multi_use_add2(i32 %A) {
+; CHECK-LABEL: define i32 @add_sext_icmp_multi_use_add2(
+; CHECK-SAME: i32 [[A:%.*]]) {
+; CHECK-NEXT:    [[ADD2:%.*]] = call i32 @llvm.umax.i32(i32 [[A]], i32 1)
+; CHECK-NEXT:    call void @use(i32 [[ADD2]])
+; CHECK-NEXT:    ret i32 [[ADD2]]
+;
+  %add1 = add i32 %A, 1
+  %icmp = icmp ne i32 %A, 0
+  %sext = sext i1 %icmp to i32
+  %add2 = add i32 %add1, %sext
+  call void @use(i32 %add2)
+  ret i32 %add2
+}
+
+define i32 @add_sext_icmp_multi_use_sext(i32 %A) {
+; CHECK-LABEL: define i32 @add_sext_icmp_multi_use_sext(
+; CHECK-SAME: i32 [[A:%.*]]) {
+; CHECK-NEXT:    [[ADD1:%.*]] = add i32 [[A]], 1
+; CHECK-NEXT:    [[ICMP:%.*]] = icmp ne i32 [[A]], 0
+; CHECK-NEXT:    [[SEXT:%.*]] = sext i1 [[ICMP]] to i32
+; CHECK-NEXT:    call void @use(i32 [[SEXT]])
+; CHECK-NEXT:    [[ADD2:%.*]] = add i32 [[ADD1]], [[SEXT]]
+; CHECK-NEXT:    ret i32 [[ADD2]]
+;
+  %add1 = add i32 %A, 1
+  %icmp = icmp ne i32 %A, 0
+  %sext = sext i1 %icmp to i32
+  call void @use(i32 %sext)
+  %add2 = add i32 %add1, %sext
+  ret i32 %add2
+}
+
+define i32 @add_sext_icmp_multi_use_icmp(i32 %A) {
+; CHECK-LABEL: define i32 @add_sext_icmp_multi_use_icmp(
+; CHECK-SAME: i32 [[A:%.*]]) {
+; CHECK-NEXT:    [[ADD1:%.*]] = add i32 [[A]], 1
+; CHECK-NEXT:    [[ICMP:%.*]] = icmp ne i32 [[A]], 0
+; CHECK-NEXT:    call void @use(i1 [[ICMP]])
+; CHECK-NEXT:    [[SEXT:%.*]] = sext i1 [[ICMP]] to i32
+; CHECK-NEXT:    [[ADD2:%.*]] = add i32 [[ADD1]], [[SEXT]]
+; CHECK-NEXT:    ret i32 [[ADD2]]
+;
+  %add1 = add i32 %A, 1
+  %icmp = icmp ne i32 %A, 0
+  call void @use(i1 %icmp)
+  %sext = sext i1 %icmp to i32
+  %add2 = add i32 %add1, %sext
+  ret i32 %add2
+}
+
+define i32 @add_sext_icmp_multi_use_add1(i32 %A) {
+; CHECK-LABEL: define i32 @add_sext_icmp_multi_use_add1(
+; CHECK-SAME: i32 [[A:%.*]]) {
+; CHECK-NEXT:    [[ADD1:%.*]] = add i32 [[A]], 1
+; CHECK-NEXT:    call void @use(i32 [[ADD1]])
+; CHECK-NEXT:    [[ICMP:%.*]] = icmp ne i32 [[A]], 0
+; CHECK-NEXT:    [[SEXT:%.*]] = sext i1 [[ICMP]] to i32
+; CHECK-NEXT:    [[ADD2:%.*]] = add i32 [[ADD1]], [[SEXT]]
+; CHECK-NEXT:    ret i32 [[ADD2]]
+;
+  %add1 = add i32 %A, 1
+  call void @use(i32 %add1)
+  %icmp = icmp ne i32 %A, 0
+  %sext = sext i1 %icmp to i32
+  %add2 = add i32 %add1, %sext
+  ret i32 %add2
+}
+
+declare void @use(i32)
+

github-actions · 2025-01-11T05:10:16Z

✅ With the latest revision this PR passed the C/C++ code formatter.

llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp

dtcxzyw

LGTM. I don't have more comments.

nikic · 2025-01-12T14:29:12Z

llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp

  }

+  // (add (add A, 1), (sext (icmp ne A, 0))) => call umax(A, 1)
+  if (match(LHS, m_OneUse(m_Add(m_Value(A), m_One()))) &&


I think we should drop the one-use check on the add at least: https://llvm.godbolt.org/z/YGq6osY3z

…ax(A, 1)

nikic

LGTM

github-actions · 2025-01-12T15:52:17Z

@Ruhung Congratulations on having your first Pull Request (PR) merged into the LLVM Project!

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Ruhung requested a review from nikic as a code owner January 10, 2025 16:38

llvmbot added llvm:instcombine Covers the InstCombine, InstSimplify and AggressiveInstCombine passes llvm:transforms labels Jan 10, 2025

This was referenced Jan 11, 2025

Task submission dtcxzyw/llvm-opt-benchmark#1312

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pre-commit: PR122491 dtcxzyw/llvm-opt-benchmark#1950

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Grep PR122491 dtcxzyw/llvm-opt-benchmark#1951

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Ruhung force-pushed the combine-dev branch from 13bc4b4 to 5107688 Compare January 11, 2025 07:02

goldsteinn requested a review from dtcxzyw January 11, 2025 21:06

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[InstCombine] Pre-commit tests

61f0c5e

Ruhung force-pushed the combine-dev branch 2 times, most recently from 746a563 to 77bd90e Compare January 12, 2025 07:56

dtcxzyw mentioned this pull request Jan 12, 2025

Fuzz PR122491 dtcxzyw/llvm-mutation-based-fuzz-service#24

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[InstCombine] Fold (add (add A, 1), (sext (icmp ne A, 0))) to call um…

e4a4e38

…ax(A, 1)

Ruhung force-pushed the combine-dev branch from 77bd90e to e4a4e38 Compare January 12, 2025 14:43

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nikic merged commit 4f7dc1b into llvm:main Jan 12, 2025
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[InstCombine] Fold (add (add A, 1), (sext (icmp ne A, 0))) to call umax(A, 1) #122491

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