[llvm] [InstCombine] Add optimization to combine adds through zext nneg, and add testcase (PR #157723)
via llvm-commits
llvm-commits at lists.llvm.org
Thu Sep 25 09:16:57 PDT 2025
https://github.com/Aethezz updated https://github.com/llvm/llvm-project/pull/157723
>From 0e8a5fd5b05517159b0df102913086d6e4bb2390 Mon Sep 17 00:00:00 2001
From: Aethezz <ellisonlao999 at gmail.com>
Date: Tue, 9 Sep 2025 13:20:22 -0400
Subject: [PATCH 1/4] Combine adds through zext nneg, and add testcase
---
.../InstCombine/InstCombineAddSub.cpp | 17 +++++++++++++++++
llvm/test/Transforms/InstCombine/zext.ll | 11 +++++++++++
2 files changed, 28 insertions(+)
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index d934638c15e75..f4a2ab5377a34 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1910,6 +1910,23 @@ Instruction *InstCombinerImpl::visitAdd(BinaryOperator &I) {
if (Instruction *Res = foldBinOpOfSelectAndCastOfSelectCondition(I))
return Res;
+ // Combine adds through zext nneg:
+ // (zext nneg (X + C1)) + C2 --> zext X if C1 + C2 == 0
+ {
+ Value *X;
+ const APInt *C1, *C2;
+ if (match(&I, m_c_Add(m_NNegZExt(m_Add(m_Value(X), m_APInt(C1))),
+ m_APInt(C2)))) {
+ // Check if the constants cancel out (C1 + C2 == 0)
+ APInt Sum = C1->sext(C2->getBitWidth()) + *C2;
+ if (Sum.isZero()) {
+ // The add inside the zext and the outer add cancel out
+ Value *NewZExt = Builder.CreateZExt(X, I.getType());
+ return replaceInstUsesWith(I, NewZExt);
+ }
+ }
+ }
+
// Re-enqueue users of the induction variable of add recurrence if we infer
// new nuw/nsw flags.
if (Changed) {
diff --git a/llvm/test/Transforms/InstCombine/zext.ll b/llvm/test/Transforms/InstCombine/zext.ll
index e4d18e9395219..15aa2aaec430a 100644
--- a/llvm/test/Transforms/InstCombine/zext.ll
+++ b/llvm/test/Transforms/InstCombine/zext.ll
@@ -976,3 +976,14 @@ entry:
%res = zext nneg i2 %x to i32
ret i32 %res
}
+
+define i32 @zext_nneg_add_cancel(i8 %arg) {
+; CHECK-LABEL: @zext_nneg_add_cancel(
+; CHECK-NEXT: [[ADD2:%.*]] = zext i8 [[ARG:%.*]] to i32
+; CHECK-NEXT: ret i32 [[ADD2]]
+;
+ %add = add i8 %arg, -2
+ %zext = zext nneg i8 %add to i32
+ %add2 = add i32 %zext, 2
+ ret i32 %add2
+}
\ No newline at end of file
>From edde23371aa6a9b94ebde072f8c09da9e244feeb Mon Sep 17 00:00:00 2001
From: Aethezz <ellisonlao999 at gmail.com>
Date: Tue, 16 Sep 2025 12:48:02 -0400
Subject: [PATCH 2/4] added preconditions and adjusted testcases
---
.../InstCombine/InstCombineAddSub.cpp | 26 ++++++++++++------
llvm/test/Transforms/InstCombine/zext.ll | 27 ++++++++++++++++++-
2 files changed, 44 insertions(+), 9 deletions(-)
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index f4a2ab5377a34..7058af37ab153 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1910,20 +1910,30 @@ Instruction *InstCombinerImpl::visitAdd(BinaryOperator &I) {
if (Instruction *Res = foldBinOpOfSelectAndCastOfSelectCondition(I))
return Res;
- // Combine adds through zext nneg:
- // (zext nneg (X + C1)) + C2 --> zext X if C1 + C2 == 0
{
Value *X;
const APInt *C1, *C2;
if (match(&I, m_c_Add(m_NNegZExt(m_Add(m_Value(X), m_APInt(C1))),
m_APInt(C2)))) {
- // Check if the constants cancel out (C1 + C2 == 0)
+ // Check if inner constant C1 is negative C1 < 0 and outer constant C2 >=
+ // 0
+ if (!C1->isNegative() || C2->isNegative())
+ return nullptr;
+
APInt Sum = C1->sext(C2->getBitWidth()) + *C2;
- if (Sum.isZero()) {
- // The add inside the zext and the outer add cancel out
- Value *NewZExt = Builder.CreateZExt(X, I.getType());
- return replaceInstUsesWith(I, NewZExt);
- }
+ APInt newSum = Sum.trunc(C1->getBitWidth());
+
+ if (newSum.sext(C2->getBitWidth()) != Sum)
+ return nullptr;
+
+ // X if sum is zero, else X + newSum
+ Value *Inner =
+ Sum.isZero()
+ ? X
+ : Builder.CreateAdd(X, ConstantInt::get(X->getType(), newSum));
+
+ Value *NewZExt = Builder.CreateZExt(Inner, I.getType());
+ return replaceInstUsesWith(I, NewZExt);
}
}
diff --git a/llvm/test/Transforms/InstCombine/zext.ll b/llvm/test/Transforms/InstCombine/zext.ll
index 15aa2aaec430a..c2622aab437af 100644
--- a/llvm/test/Transforms/InstCombine/zext.ll
+++ b/llvm/test/Transforms/InstCombine/zext.ll
@@ -986,4 +986,29 @@ define i32 @zext_nneg_add_cancel(i8 %arg) {
%zext = zext nneg i8 %add to i32
%add2 = add i32 %zext, 2
ret i32 %add2
-}
\ No newline at end of file
+}
+
+define i32 @zext_nneg_no_cancel(i8 %arg) {
+; CHECK-LABEL: @zext_nneg_no_cancel(
+; CHECK-NEXT: [[TMP1:%.*]] = add i8 [[ARG:%.*]], -1
+; CHECK-NEXT: [[ADD2:%.*]] = zext i8 [[TMP1]] to i32
+; CHECK-NEXT: ret i32 [[ADD2]]
+;
+ %add = add i8 %arg, -2
+ %zext = zext nneg i8 %add to i32
+ %add2 = add i32 %zext, 1
+ ret i32 %add2
+}
+
+define i32 @zext_nneg_overflow(i8 %arg) {
+; CHECK-LABEL: @zext_nneg_overflow(
+; CHECK-NEXT: [[ADD:%.*]] = add i8 [[ARG:%.*]], -2
+; CHECK-NEXT: [[ZEXT:%.*]] = zext nneg i8 [[ADD]] to i32
+; CHECK-NEXT: [[ADD2:%.*]] = add nuw nsw i32 [[ZEXT]], 299
+; CHECK-NEXT: ret i32 [[ADD2]]
+;
+ %add = add i8 %arg, -2
+ %zext = zext nneg i8 %add to i32
+ %add2 = add i32 %zext, 299
+ ret i32 %add2
+}
>From 93612576fa58811a72d127fb8d02ddf8f04fe56f Mon Sep 17 00:00:00 2001
From: Aethezz <ellisonlao999 at gmail.com>
Date: Wed, 24 Sep 2025 11:21:35 -0400
Subject: [PATCH 3/4] update review and added multiuse
---
.../InstCombine/InstCombineAddSub.cpp | 9 ++--
llvm/test/Transforms/InstCombine/zext.ll | 46 +++++++++++++++++++
2 files changed, 50 insertions(+), 5 deletions(-)
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index 7058af37ab153..1a339e2620e82 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1913,8 +1913,8 @@ Instruction *InstCombinerImpl::visitAdd(BinaryOperator &I) {
{
Value *X;
const APInt *C1, *C2;
- if (match(&I, m_c_Add(m_NNegZExt(m_Add(m_Value(X), m_APInt(C1))),
- m_APInt(C2)))) {
+ if (match(&I,
+ m_Add(m_NNegZExt(m_Add(m_Value(X), m_APInt(C1))), m_APInt(C2)))) {
// Check if inner constant C1 is negative C1 < 0 and outer constant C2 >=
// 0
if (!C1->isNegative() || C2->isNegative())
@@ -1923,7 +1923,7 @@ Instruction *InstCombinerImpl::visitAdd(BinaryOperator &I) {
APInt Sum = C1->sext(C2->getBitWidth()) + *C2;
APInt newSum = Sum.trunc(C1->getBitWidth());
- if (newSum.sext(C2->getBitWidth()) != Sum)
+ if (!Sum.isSignedIntN(C1->getBitWidth()))
return nullptr;
// X if sum is zero, else X + newSum
@@ -1932,8 +1932,7 @@ Instruction *InstCombinerImpl::visitAdd(BinaryOperator &I) {
? X
: Builder.CreateAdd(X, ConstantInt::get(X->getType(), newSum));
- Value *NewZExt = Builder.CreateZExt(Inner, I.getType());
- return replaceInstUsesWith(I, NewZExt);
+ return new ZExtInst(Inner, I.getType());
}
}
diff --git a/llvm/test/Transforms/InstCombine/zext.ll b/llvm/test/Transforms/InstCombine/zext.ll
index c2622aab437af..5b3e7caea3bb8 100644
--- a/llvm/test/Transforms/InstCombine/zext.ll
+++ b/llvm/test/Transforms/InstCombine/zext.ll
@@ -988,6 +988,21 @@ define i32 @zext_nneg_add_cancel(i8 %arg) {
ret i32 %add2
}
+define i32 @zext_nneg_add_cancel_multi_use(i8 %arg) {
+; CHECK-LABEL: @zext_nneg_add_cancel_multi_use(
+; CHECK-NEXT: [[ADD:%.*]] = add i8 [[ARG:%.*]], -2
+; CHECK-NEXT: [[ZEXT:%.*]] = zext nneg i8 [[ADD]] to i32
+; CHECK-NEXT: call void @use32(i32 [[ZEXT]])
+; CHECK-NEXT: [[ADD2:%.*]] = zext i8 [[ARG]] to i32
+; CHECK-NEXT: ret i32 [[ADD2]]
+;
+ %add = add i8 %arg, -2
+ %zext = zext nneg i8 %add to i32
+ call void @use32(i32 %zext)
+ %add2 = add i32 %zext, 2
+ ret i32 %add2
+}
+
define i32 @zext_nneg_no_cancel(i8 %arg) {
; CHECK-LABEL: @zext_nneg_no_cancel(
; CHECK-NEXT: [[TMP1:%.*]] = add i8 [[ARG:%.*]], -1
@@ -1000,6 +1015,22 @@ define i32 @zext_nneg_no_cancel(i8 %arg) {
ret i32 %add2
}
+define i32 @zext_nneg_no_cancel_multi_use(i8 %arg) {
+; CHECK-LABEL: @zext_nneg_no_cancel_multi_use(
+; CHECK-NEXT: [[ADD:%.*]] = add i8 [[ARG:%.*]], -2
+; CHECK-NEXT: [[ZEXT:%.*]] = zext nneg i8 [[ADD]] to i32
+; CHECK-NEXT: call void @use32(i32 [[ZEXT]])
+; CHECK-NEXT: [[TMP1:%.*]] = add i8 [[ARG]], -1
+; CHECK-NEXT: [[ADD2:%.*]] = zext i8 [[TMP1]] to i32
+; CHECK-NEXT: ret i32 [[ADD2]]
+;
+ %add = add i8 %arg, -2
+ %zext = zext nneg i8 %add to i32
+ call void @use32(i32 %zext)
+ %add2 = add i32 %zext, 1
+ ret i32 %add2
+}
+
define i32 @zext_nneg_overflow(i8 %arg) {
; CHECK-LABEL: @zext_nneg_overflow(
; CHECK-NEXT: [[ADD:%.*]] = add i8 [[ARG:%.*]], -2
@@ -1012,3 +1043,18 @@ define i32 @zext_nneg_overflow(i8 %arg) {
%add2 = add i32 %zext, 299
ret i32 %add2
}
+
+define i32 @zext_nneg_overflow_multi_use(i8 %arg) {
+; CHECK-LABEL: @zext_nneg_overflow_multi_use(
+; CHECK-NEXT: [[ADD:%.*]] = add i8 [[ARG:%.*]], -2
+; CHECK-NEXT: [[ZEXT:%.*]] = zext nneg i8 [[ADD]] to i32
+; CHECK-NEXT: call void @use32(i32 [[ZEXT]])
+; CHECK-NEXT: [[ADD2:%.*]] = add nuw nsw i32 [[ZEXT]], 299
+; CHECK-NEXT: ret i32 [[ADD2]]
+;
+ %add = add i8 %arg, -2
+ %zext = zext nneg i8 %add to i32
+ call void @use32(i32 %zext)
+ %add2 = add i32 %zext, 299
+ ret i32 %add2
+}
>From 0f37733f316a75e44270c0ce46d85ccc8172e65a Mon Sep 17 00:00:00 2001
From: Aethezz <ellisonlao999 at gmail.com>
Date: Thu, 25 Sep 2025 12:16:26 -0400
Subject: [PATCH 4/4] fix extra case and multiuse
---
.../InstCombine/InstCombineAddSub.cpp | 27 +++++++++++++------
llvm/test/Transforms/InstCombine/zext.ll | 17 +-----------
2 files changed, 20 insertions(+), 24 deletions(-)
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index 1a339e2620e82..8d4a2a11d235e 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1915,22 +1915,33 @@ Instruction *InstCombinerImpl::visitAdd(BinaryOperator &I) {
const APInt *C1, *C2;
if (match(&I,
m_Add(m_NNegZExt(m_Add(m_Value(X), m_APInt(C1))), m_APInt(C2)))) {
- // Check if inner constant C1 is negative C1 < 0 and outer constant C2 >=
- // 0
+ // Check if inner const C1 is negative C1 < 0 and outer const C2 >= 0
if (!C1->isNegative() || C2->isNegative())
return nullptr;
APInt Sum = C1->sext(C2->getBitWidth()) + *C2;
- APInt newSum = Sum.trunc(C1->getBitWidth());
if (!Sum.isSignedIntN(C1->getBitWidth()))
return nullptr;
- // X if sum is zero, else X + newSum
- Value *Inner =
- Sum.isZero()
- ? X
- : Builder.CreateAdd(X, ConstantInt::get(X->getType(), newSum));
+ Value *Inner;
+
+ if (Sum.isZero()) {
+ Inner = X;
+ } else {
+ unsigned XWidth = X->getType()->getIntegerBitWidth();
+ APInt MinX = APInt::getSignedMinValue(XWidth);
+ if ((MinX + Sum.trunc(XWidth)).isNegative())
+ return nullptr;
+
+ auto *ZExt = cast<ZExtInst>(I.getOperand(0));
+ auto *InnerAdd = ZExt->getOperand(0);
+ if (!ZExt->hasOneUse() || !InnerAdd->hasOneUse())
+ return nullptr;
+
+ Inner = Builder.CreateAdd(
+ X, ConstantInt::get(X->getType(), Sum.trunc(C1->getBitWidth())));
+ }
return new ZExtInst(Inner, I.getType());
}
diff --git a/llvm/test/Transforms/InstCombine/zext.ll b/llvm/test/Transforms/InstCombine/zext.ll
index 5b3e7caea3bb8..2f9cbcdf00218 100644
--- a/llvm/test/Transforms/InstCombine/zext.ll
+++ b/llvm/test/Transforms/InstCombine/zext.ll
@@ -1020,8 +1020,7 @@ define i32 @zext_nneg_no_cancel_multi_use(i8 %arg) {
; CHECK-NEXT: [[ADD:%.*]] = add i8 [[ARG:%.*]], -2
; CHECK-NEXT: [[ZEXT:%.*]] = zext nneg i8 [[ADD]] to i32
; CHECK-NEXT: call void @use32(i32 [[ZEXT]])
-; CHECK-NEXT: [[TMP1:%.*]] = add i8 [[ARG]], -1
-; CHECK-NEXT: [[ADD2:%.*]] = zext i8 [[TMP1]] to i32
+; CHECK-NEXT: [[ADD2:%.*]] = add nuw nsw i32 [[ZEXT]], 1
; CHECK-NEXT: ret i32 [[ADD2]]
;
%add = add i8 %arg, -2
@@ -1044,17 +1043,3 @@ define i32 @zext_nneg_overflow(i8 %arg) {
ret i32 %add2
}
-define i32 @zext_nneg_overflow_multi_use(i8 %arg) {
-; CHECK-LABEL: @zext_nneg_overflow_multi_use(
-; CHECK-NEXT: [[ADD:%.*]] = add i8 [[ARG:%.*]], -2
-; CHECK-NEXT: [[ZEXT:%.*]] = zext nneg i8 [[ADD]] to i32
-; CHECK-NEXT: call void @use32(i32 [[ZEXT]])
-; CHECK-NEXT: [[ADD2:%.*]] = add nuw nsw i32 [[ZEXT]], 299
-; CHECK-NEXT: ret i32 [[ADD2]]
-;
- %add = add i8 %arg, -2
- %zext = zext nneg i8 %add to i32
- call void @use32(i32 %zext)
- %add2 = add i32 %zext, 299
- ret i32 %add2
-}
More information about the llvm-commits
mailing list