[llvm] [InstCombine] KnownBits::isNonNegative should recognize `b - a` after `a <= b` (PR #145105)
Ross Kirsling via llvm-commits
llvm-commits at lists.llvm.org
Mon Jun 23 12:54:53 PDT 2025
https://github.com/rkirsling updated https://github.com/llvm/llvm-project/pull/145105
>From e6612fe4290bd154e981569b92565f551ce21a21 Mon Sep 17 00:00:00 2001
From: Ross Kirsling <ross.kirsling at sony.com>
Date: Fri, 20 Jun 2025 11:46:11 -0700
Subject: [PATCH 1/8] Add test case.
---
.../sub-after-sle-is-non-negative.ll | 53 +++++++++++++++++++
1 file changed, 53 insertions(+)
create mode 100644 llvm/test/Transforms/InstCombine/sub-after-sle-is-non-negative.ll
diff --git a/llvm/test/Transforms/InstCombine/sub-after-sle-is-non-negative.ll b/llvm/test/Transforms/InstCombine/sub-after-sle-is-non-negative.ll
new file mode 100644
index 0000000000000..b4427b72ff8a5
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/sub-after-sle-is-non-negative.ll
@@ -0,0 +1,53 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt < %s -passes=instcombine -S | FileCheck %s
+define void @test_as_arg(i8 %a, i8 %b) {
+; CHECK-LABEL: define void @test_as_arg(
+; CHECK-SAME: i8 [[A:%.*]], i8 [[B:%.*]]) {
+; CHECK-NEXT: [[CMP:%.*]] = icmp sgt i8 [[A]], [[B]]
+; CHECK-NEXT: br i1 [[CMP]], label %[[COND_END:.*]], label %[[COND_FALSE:.*]]
+; CHECK: [[COND_FALSE]]:
+; CHECK-NEXT: [[SUB:%.*]] = sub nsw i8 [[B]], [[A]]
+; CHECK-NEXT: [[CONV:%.*]] = sext i8 [[SUB]] to i16
+; CHECK-NEXT: call void @subroutine(i16 [[CONV]])
+; CHECK-NEXT: br label %[[COND_END]]
+; CHECK: [[COND_END]]:
+; CHECK-NEXT: ret void
+;
+ %cmp = icmp sgt i8 %a, %b
+ br i1 %cmp, label %cond.end, label %cond.false
+
+cond.false:
+ %sub = sub nsw i8 %b, %a
+ %conv = sext i8 %sub to i16
+ call void @subroutine(i16 %conv)
+ br label %cond.end
+
+cond.end:
+ ret void
+}
+
+declare void @subroutine(i16)
+
+define i16 @test_as_retval(i8 %a, i8 %b) {
+; CHECK-LABEL: define i16 @test_as_retval(
+; CHECK-SAME: i8 [[A:%.*]], i8 [[B:%.*]]) {
+; CHECK-NEXT: [[CMP:%.*]] = icmp sgt i8 [[A]], [[B]]
+; CHECK-NEXT: br i1 [[CMP]], label %[[COND_TRUE:.*]], label %[[COND_FALSE:.*]]
+; CHECK: [[COND_TRUE]]:
+; CHECK-NEXT: ret i16 0
+; CHECK: [[COND_FALSE]]:
+; CHECK-NEXT: [[SUB:%.*]] = sub nsw i8 [[B]], [[A]]
+; CHECK-NEXT: [[CONV:%.*]] = sext i8 [[SUB]] to i16
+; CHECK-NEXT: ret i16 [[CONV]]
+;
+ %cmp = icmp sgt i8 %a, %b
+ br i1 %cmp, label %cond.true, label %cond.false
+
+cond.true:
+ ret i16 0
+
+cond.false:
+ %sub = sub nsw i8 %b, %a
+ %conv = sext i8 %sub to i16
+ ret i16 %conv
+}
>From d80031d1c511b91b86f9333a6a32c24c52b7ad32 Mon Sep 17 00:00:00 2001
From: Ross Kirsling <ross.kirsling at sony.com>
Date: Fri, 20 Jun 2025 11:46:58 -0700
Subject: [PATCH 2/8] Address issue.
---
llvm/lib/Analysis/ValueTracking.cpp | 11 ++++++++++-
.../InstCombine/sub-after-sle-is-non-negative.ll | 4 ++--
2 files changed, 12 insertions(+), 3 deletions(-)
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 73320b556f825..be9843503298f 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -278,7 +278,16 @@ static bool isKnownNonZero(const Value *V, const APInt &DemandedElts,
bool llvm::isKnownNonNegative(const Value *V, const SimplifyQuery &SQ,
unsigned Depth) {
- return computeKnownBits(V, SQ, Depth).isNonNegative();
+ if (computeKnownBits(V, SQ, Depth).isNonNegative())
+ return true;
+
+ Value *X, *Y;
+ if (match(V, m_NSWSub(m_Value(X), m_Value(Y))))
+ if (std::optional<bool> result =
+ isImpliedByDomCondition(ICmpInst::ICMP_SLE, Y, X, SQ.CxtI, SQ.DL))
+ return *result;
+
+ return false;
}
bool llvm::isKnownPositive(const Value *V, const SimplifyQuery &SQ,
diff --git a/llvm/test/Transforms/InstCombine/sub-after-sle-is-non-negative.ll b/llvm/test/Transforms/InstCombine/sub-after-sle-is-non-negative.ll
index b4427b72ff8a5..279a6de4125ed 100644
--- a/llvm/test/Transforms/InstCombine/sub-after-sle-is-non-negative.ll
+++ b/llvm/test/Transforms/InstCombine/sub-after-sle-is-non-negative.ll
@@ -7,7 +7,7 @@ define void @test_as_arg(i8 %a, i8 %b) {
; CHECK-NEXT: br i1 [[CMP]], label %[[COND_END:.*]], label %[[COND_FALSE:.*]]
; CHECK: [[COND_FALSE]]:
; CHECK-NEXT: [[SUB:%.*]] = sub nsw i8 [[B]], [[A]]
-; CHECK-NEXT: [[CONV:%.*]] = sext i8 [[SUB]] to i16
+; CHECK-NEXT: [[CONV:%.*]] = zext nneg i8 [[SUB]] to i16
; CHECK-NEXT: call void @subroutine(i16 [[CONV]])
; CHECK-NEXT: br label %[[COND_END]]
; CHECK: [[COND_END]]:
@@ -37,7 +37,7 @@ define i16 @test_as_retval(i8 %a, i8 %b) {
; CHECK-NEXT: ret i16 0
; CHECK: [[COND_FALSE]]:
; CHECK-NEXT: [[SUB:%.*]] = sub nsw i8 [[B]], [[A]]
-; CHECK-NEXT: [[CONV:%.*]] = sext i8 [[SUB]] to i16
+; CHECK-NEXT: [[CONV:%.*]] = zext nneg i8 [[SUB]] to i16
; CHECK-NEXT: ret i16 [[CONV]]
;
%cmp = icmp sgt i8 %a, %b
>From 905381cae7795093d3a31af58ba7eb155b814f71 Mon Sep 17 00:00:00 2001
From: Ross Kirsling <ross.kirsling at sony.com>
Date: Fri, 20 Jun 2025 21:53:59 -0700
Subject: [PATCH 3/8] rebuild linux
>From 823ede1bea906881208f8e94994d1ff1fec59f53 Mon Sep 17 00:00:00 2001
From: Ross Kirsling <ross.kirsling at sony.com>
Date: Sun, 22 Jun 2025 18:13:18 -0700
Subject: [PATCH 4/8] Add negative tests.
---
.../sub-after-sle-is-non-negative.ll | 54 ++++++++++++++++++-
1 file changed, 52 insertions(+), 2 deletions(-)
diff --git a/llvm/test/Transforms/InstCombine/sub-after-sle-is-non-negative.ll b/llvm/test/Transforms/InstCombine/sub-after-sle-is-non-negative.ll
index 279a6de4125ed..a282236850135 100644
--- a/llvm/test/Transforms/InstCombine/sub-after-sle-is-non-negative.ll
+++ b/llvm/test/Transforms/InstCombine/sub-after-sle-is-non-negative.ll
@@ -1,5 +1,7 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
; RUN: opt < %s -passes=instcombine -S | FileCheck %s
+declare void @subroutine(i16)
+
define void @test_as_arg(i8 %a, i8 %b) {
; CHECK-LABEL: define void @test_as_arg(
; CHECK-SAME: i8 [[A:%.*]], i8 [[B:%.*]]) {
@@ -26,8 +28,6 @@ cond.end:
ret void
}
-declare void @subroutine(i16)
-
define i16 @test_as_retval(i8 %a, i8 %b) {
; CHECK-LABEL: define i16 @test_as_retval(
; CHECK-SAME: i8 [[A:%.*]], i8 [[B:%.*]]) {
@@ -51,3 +51,53 @@ cond.false:
%conv = sext i8 %sub to i16
ret i16 %conv
}
+
+define void @test_as_arg_neg(i8 %a, i8 %b) {
+; CHECK-LABEL: define void @test_as_arg_neg(
+; CHECK-SAME: i8 [[A:%.*]], i8 [[B:%.*]]) {
+; CHECK-NEXT: [[CMP:%.*]] = icmp slt i8 [[A]], [[B]]
+; CHECK-NEXT: br i1 [[CMP]], label %[[COND_END:.*]], label %[[COND_FALSE:.*]]
+; CHECK: [[COND_FALSE]]:
+; CHECK-NEXT: [[SUB:%.*]] = sub nsw i8 [[B]], [[A]]
+; CHECK-NEXT: [[CONV:%.*]] = sext i8 [[SUB]] to i16
+; CHECK-NEXT: call void @subroutine(i16 [[CONV]])
+; CHECK-NEXT: br label %[[COND_END]]
+; CHECK: [[COND_END]]:
+; CHECK-NEXT: ret void
+;
+ %cmp = icmp slt i8 %a, %b
+ br i1 %cmp, label %cond.end, label %cond.false
+
+cond.false:
+ %sub = sub nsw i8 %b, %a
+ %conv = sext i8 %sub to i16
+ call void @subroutine(i16 %conv)
+ br label %cond.end
+
+cond.end:
+ ret void
+}
+
+define i16 @test_as_retval_neg(i8 %a, i8 %b) {
+; CHECK-LABEL: define i16 @test_as_retval_neg(
+; CHECK-SAME: i8 [[A:%.*]], i8 [[B:%.*]]) {
+; CHECK-NEXT: [[CMP:%.*]] = icmp slt i8 [[A]], [[B]]
+; CHECK-NEXT: br i1 [[CMP]], label %[[COND_TRUE:.*]], label %[[COND_FALSE:.*]]
+; CHECK: [[COND_TRUE]]:
+; CHECK-NEXT: ret i16 0
+; CHECK: [[COND_FALSE]]:
+; CHECK-NEXT: [[SUB:%.*]] = sub nsw i8 [[B]], [[A]]
+; CHECK-NEXT: [[CONV:%.*]] = sext i8 [[SUB]] to i16
+; CHECK-NEXT: ret i16 [[CONV]]
+;
+ %cmp = icmp slt i8 %a, %b
+ br i1 %cmp, label %cond.true, label %cond.false
+
+cond.true:
+ ret i16 0
+
+cond.false:
+ %sub = sub nsw i8 %b, %a
+ %conv = sext i8 %sub to i16
+ ret i16 %conv
+}
>From b4e86030c10c90550e39e48226fc6e87d59f7550 Mon Sep 17 00:00:00 2001
From: Ross Kirsling <ross.kirsling at sony.com>
Date: Sun, 22 Jun 2025 18:20:32 -0700
Subject: [PATCH 5/8] Move logic into computeKnownBits.
---
llvm/lib/Analysis/ValueTracking.cpp | 17 +++++++----------
1 file changed, 7 insertions(+), 10 deletions(-)
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index be9843503298f..bf017ded68b52 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -278,16 +278,7 @@ static bool isKnownNonZero(const Value *V, const APInt &DemandedElts,
bool llvm::isKnownNonNegative(const Value *V, const SimplifyQuery &SQ,
unsigned Depth) {
- if (computeKnownBits(V, SQ, Depth).isNonNegative())
- return true;
-
- Value *X, *Y;
- if (match(V, m_NSWSub(m_Value(X), m_Value(Y))))
- if (std::optional<bool> result =
- isImpliedByDomCondition(ICmpInst::ICMP_SLE, Y, X, SQ.CxtI, SQ.DL))
- return *result;
-
- return false;
+ return computeKnownBits(V, SQ, Depth).isNonNegative();
}
bool llvm::isKnownPositive(const Value *V, const SimplifyQuery &SQ,
@@ -371,6 +362,12 @@ static void computeKnownBitsAddSub(bool Add, const Value *Op0, const Value *Op1,
computeKnownBits(Op0, DemandedElts, Known2, Q, Depth + 1);
KnownOut = KnownBits::computeForAddSub(Add, NSW, NUW, Known2, KnownOut);
+
+ if (!Add && NSW)
+ if (std::optional<bool> result =
+ isImpliedByDomCondition(ICmpInst::ICMP_SLE, Op1, Op0, Q.CxtI, Q.DL);
+ *result)
+ KnownOut.makeNonNegative();
}
static void computeKnownBitsMul(const Value *Op0, const Value *Op1, bool NSW,
>From 68cb10e5d3b44bf74f7e7da189e95465654443c1 Mon Sep 17 00:00:00 2001
From: Ross Kirsling <ross.kirsling at sony.com>
Date: Sun, 22 Jun 2025 22:15:45 -0700
Subject: [PATCH 6/8] Address feedback
---
llvm/lib/Analysis/ValueTracking.cpp | 9 ++++-----
1 file changed, 4 insertions(+), 5 deletions(-)
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 5a20169cdc2d9..7cedcad6af862 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -363,11 +363,10 @@ static void computeKnownBitsAddSub(bool Add, const Value *Op0, const Value *Op1,
computeKnownBits(Op0, DemandedElts, Known2, Q, Depth + 1);
KnownOut = KnownBits::computeForAddSub(Add, NSW, NUW, Known2, KnownOut);
- if (!Add && NSW)
- if (std::optional<bool> result =
- isImpliedByDomCondition(ICmpInst::ICMP_SLE, Op1, Op0, Q.CxtI, Q.DL);
- *result)
- KnownOut.makeNonNegative();
+ if (!Add && NSW &&
+ isImpliedByDomCondition(ICmpInst::ICMP_SLE, Op1, Op0, Q.CxtI, Q.DL)
+ .value_or(false))
+ KnownOut.makeNonNegative();
}
static void computeKnownBitsMul(const Value *Op0, const Value *Op1, bool NSW,
>From 1ecadd1f920f09b566c3e3c80cf0cfa3cb8ae5ee Mon Sep 17 00:00:00 2001
From: Ross Kirsling <ross.kirsling at sony.com>
Date: Mon, 23 Jun 2025 10:45:19 -0700
Subject: [PATCH 7/8] Address nikic's feedback.
---
llvm/lib/Analysis/ValueTracking.cpp | 2 +-
.../sub-after-sle-is-non-negative.ll | 58 +++++++++++++++++--
2 files changed, 55 insertions(+), 5 deletions(-)
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 7cedcad6af862..b226eaf310f3b 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -363,7 +363,7 @@ static void computeKnownBitsAddSub(bool Add, const Value *Op0, const Value *Op1,
computeKnownBits(Op0, DemandedElts, Known2, Q, Depth + 1);
KnownOut = KnownBits::computeForAddSub(Add, NSW, NUW, Known2, KnownOut);
- if (!Add && NSW &&
+ if (!Add && NSW && !KnownOut.isNonNegative() &&
isImpliedByDomCondition(ICmpInst::ICMP_SLE, Op1, Op0, Q.CxtI, Q.DL)
.value_or(false))
KnownOut.makeNonNegative();
diff --git a/llvm/test/Transforms/InstCombine/sub-after-sle-is-non-negative.ll b/llvm/test/Transforms/InstCombine/sub-after-sle-is-non-negative.ll
index a282236850135..8395895b1af65 100644
--- a/llvm/test/Transforms/InstCombine/sub-after-sle-is-non-negative.ll
+++ b/llvm/test/Transforms/InstCombine/sub-after-sle-is-non-negative.ll
@@ -52,8 +52,8 @@ cond.false:
ret i16 %conv
}
-define void @test_as_arg_neg(i8 %a, i8 %b) {
-; CHECK-LABEL: define void @test_as_arg_neg(
+define void @test_as_arg_wrong_icmp(i8 %a, i8 %b) {
+; CHECK-LABEL: define void @test_as_arg_wrong_icmp(
; CHECK-SAME: i8 [[A:%.*]], i8 [[B:%.*]]) {
; CHECK-NEXT: [[CMP:%.*]] = icmp slt i8 [[A]], [[B]]
; CHECK-NEXT: br i1 [[CMP]], label %[[COND_END:.*]], label %[[COND_FALSE:.*]]
@@ -78,8 +78,34 @@ cond.end:
ret void
}
-define i16 @test_as_retval_neg(i8 %a, i8 %b) {
-; CHECK-LABEL: define i16 @test_as_retval_neg(
+define void @test_as_arg_missing_nsw(i8 %a, i8 %b) {
+; CHECK-LABEL: define void @test_as_arg_missing_nsw(
+; CHECK-SAME: i8 [[A:%.*]], i8 [[B:%.*]]) {
+; CHECK-NEXT: [[CMP:%.*]] = icmp sgt i8 [[A]], [[B]]
+; CHECK-NEXT: br i1 [[CMP]], label %[[COND_END:.*]], label %[[COND_FALSE:.*]]
+; CHECK: [[COND_FALSE]]:
+; CHECK-NEXT: [[SUB:%.*]] = sub i8 [[B]], [[A]]
+; CHECK-NEXT: [[CONV:%.*]] = sext i8 [[SUB]] to i16
+; CHECK-NEXT: call void @subroutine(i16 [[CONV]])
+; CHECK-NEXT: br label %[[COND_END]]
+; CHECK: [[COND_END]]:
+; CHECK-NEXT: ret void
+;
+ %cmp = icmp sgt i8 %a, %b
+ br i1 %cmp, label %cond.end, label %cond.false
+
+cond.false:
+ %sub = sub i8 %b, %a
+ %conv = sext i8 %sub to i16
+ call void @subroutine(i16 %conv)
+ br label %cond.end
+
+cond.end:
+ ret void
+}
+
+define i16 @test_as_retval_wrong_icmp(i8 %a, i8 %b) {
+; CHECK-LABEL: define i16 @test_as_retval_wrong_icmp(
; CHECK-SAME: i8 [[A:%.*]], i8 [[B:%.*]]) {
; CHECK-NEXT: [[CMP:%.*]] = icmp slt i8 [[A]], [[B]]
; CHECK-NEXT: br i1 [[CMP]], label %[[COND_TRUE:.*]], label %[[COND_FALSE:.*]]
@@ -101,3 +127,27 @@ cond.false:
%conv = sext i8 %sub to i16
ret i16 %conv
}
+
+define i16 @test_as_retval_missing_nsw(i8 %a, i8 %b) {
+; CHECK-LABEL: define i16 @test_as_retval_missing_nsw(
+; CHECK-SAME: i8 [[A:%.*]], i8 [[B:%.*]]) {
+; CHECK-NEXT: [[CMP:%.*]] = icmp sgt i8 [[A]], [[B]]
+; CHECK-NEXT: br i1 [[CMP]], label %[[COND_TRUE:.*]], label %[[COND_FALSE:.*]]
+; CHECK: [[COND_TRUE]]:
+; CHECK-NEXT: ret i16 0
+; CHECK: [[COND_FALSE]]:
+; CHECK-NEXT: [[SUB:%.*]] = sub i8 [[B]], [[A]]
+; CHECK-NEXT: [[CONV:%.*]] = sext i8 [[SUB]] to i16
+; CHECK-NEXT: ret i16 [[CONV]]
+;
+ %cmp = icmp sgt i8 %a, %b
+ br i1 %cmp, label %cond.true, label %cond.false
+
+cond.true:
+ ret i16 0
+
+cond.false:
+ %sub = sub i8 %b, %a
+ %conv = sext i8 %sub to i16
+ ret i16 %conv
+}
>From 90d0f801d4ba52b0610cb86970949ed6681731cb Mon Sep 17 00:00:00 2001
From: Ross Kirsling <ross.kirsling at sony.com>
Date: Mon, 23 Jun 2025 12:54:38 -0700
Subject: [PATCH 8/8] rebuild linux
More information about the llvm-commits
mailing list