[llvm] InstSimplify: teach simplifyICmpWithConstant about samesign (PR #125899)

Ramkumar Ramachandra via llvm-commits llvm-commits at lists.llvm.org
Fri Feb 7 10:46:44 PST 2025


https://github.com/artagnon updated https://github.com/llvm/llvm-project/pull/125899

>From 193c879abdab710dbfd1758746235303bb5b9024 Mon Sep 17 00:00:00 2001
From: Ramkumar Ramachandra <ramkumar.ramachandra at codasip.com>
Date: Wed, 5 Feb 2025 15:56:35 +0000
Subject: [PATCH 1/2] ValueTracking: pre-commit constrange-samesign tests

---
 .../Analysis/ValueTracking/constant-ranges.ll | 40 +++++++++++++++++++
 1 file changed, 40 insertions(+)

diff --git a/llvm/test/Analysis/ValueTracking/constant-ranges.ll b/llvm/test/Analysis/ValueTracking/constant-ranges.ll
index c440cfad889d3b4..7a4b9f7ed645a9f 100644
--- a/llvm/test/Analysis/ValueTracking/constant-ranges.ll
+++ b/llvm/test/Analysis/ValueTracking/constant-ranges.ll
@@ -160,6 +160,15 @@ define i1 @srem_posC_okay0(i8 %x) {
   ret i1 %r
 }
 
+define i1 @srem_posC_okay0_samesign(i8 %x) {
+; CHECK-LABEL: @srem_posC_okay0_samesign(
+; CHECK-NEXT:    ret i1 true
+;
+  %val = srem i8 34, %x
+  %r = icmp samesign ule i8 %val, 34
+  ret i1 %r
+}
+
 define i1 @srem_posC_okay1(i8 %x) {
 ; CHECK-LABEL: @srem_posC_okay1(
 ; CHECK-NEXT:    ret i1 true
@@ -169,6 +178,15 @@ define i1 @srem_posC_okay1(i8 %x) {
   ret i1 %r
 }
 
+define i1 @srem_posC_okay1_samesign(i8 %x) {
+; CHECK-LABEL: @srem_posC_okay1_samesign(
+; CHECK-NEXT:    ret i1 false
+;
+  %val = srem i8 34, %x
+  %r = icmp samesign uge i8 %val, -3
+  ret i1 %r
+}
+
 define i1 @srem_negC_okay0(i8 %x) {
 ; CHECK-LABEL: @srem_negC_okay0(
 ; CHECK-NEXT:    ret i1 true
@@ -178,6 +196,17 @@ define i1 @srem_negC_okay0(i8 %x) {
   ret i1 %r
 }
 
+define i1 @srem_negC_okay0_samesign(i8 %x) {
+; CHECK-LABEL: @srem_negC_okay0_samesign(
+; CHECK-NEXT:    [[VAL:%.*]] = srem i8 -34, [[X:%.*]]
+; CHECK-NEXT:    [[R:%.*]] = icmp samesign ule i8 [[VAL]], 0
+; CHECK-NEXT:    ret i1 [[R]]
+;
+  %val = srem i8 -34, %x
+  %r = icmp samesign ule i8 %val, 0
+  ret i1 %r
+}
+
 define i1 @srem_negC_okay1(i8 %x) {
 ; CHECK-LABEL: @srem_negC_okay1(
 ; CHECK-NEXT:    ret i1 true
@@ -187,6 +216,17 @@ define i1 @srem_negC_okay1(i8 %x) {
   ret i1 %r
 }
 
+define i1 @srem_negC_okay1_samesign(i8 %x) {
+; CHECK-LABEL: @srem_negC_okay1_samesign(
+; CHECK-NEXT:    [[VAL:%.*]] = srem i8 -34, [[X:%.*]]
+; CHECK-NEXT:    [[R:%.*]] = icmp samesign uge i8 [[VAL]], -34
+; CHECK-NEXT:    ret i1 [[R]]
+;
+  %val = srem i8 -34, %x
+  %r = icmp samesign uge i8 %val, -34
+  ret i1 %r
+}
+
 define i1 @srem_posC_fail0(i8 %x) {
 ; CHECK-LABEL: @srem_posC_fail0(
 ; CHECK-NEXT:    [[VAL:%.*]] = srem i8 34, [[X:%.*]]

>From f9a2becc1a6c346a17e103979d93c6b2838d65a4 Mon Sep 17 00:00:00 2001
From: Ramkumar Ramachandra <ramkumar.ramachandra at codasip.com>
Date: Wed, 5 Feb 2025 17:46:48 +0000
Subject: [PATCH 2/2] InstSimplify: teach simplifyICmpWithConstant about
 samesign

We have chosen to change ConstantRange::makeAllowedICmpRegion to respect
samesign information, noting that ConstantRange::makeExactICmpRegion
should not be modified.
---
 llvm/include/llvm/IR/ConstantRange.h                |  7 ++++++-
 llvm/lib/Analysis/InstructionSimplify.cpp           |  2 +-
 llvm/lib/IR/ConstantRange.cpp                       |  8 ++++++++
 llvm/test/Analysis/ValueTracking/constant-ranges.ll | 10 +++-------
 4 files changed, 18 insertions(+), 9 deletions(-)

diff --git a/llvm/include/llvm/IR/ConstantRange.h b/llvm/include/llvm/IR/ConstantRange.h
index d086c25390fd227..f530e0a2e59df00 100644
--- a/llvm/include/llvm/IR/ConstantRange.h
+++ b/llvm/include/llvm/IR/ConstantRange.h
@@ -34,7 +34,6 @@
 #include "llvm/ADT/APInt.h"
 #include "llvm/IR/InstrTypes.h"
 #include "llvm/IR/Instruction.h"
-#include "llvm/Support/Compiler.h"
 #include <cstdint>
 
 namespace llvm {
@@ -42,6 +41,7 @@ namespace llvm {
 class MDNode;
 class raw_ostream;
 struct KnownBits;
+class CmpPredicate;
 
 /// This class represents a range of values.
 class [[nodiscard]] ConstantRange {
@@ -103,6 +103,11 @@ class [[nodiscard]] ConstantRange {
   static ConstantRange makeAllowedICmpRegion(CmpInst::Predicate Pred,
                                              const ConstantRange &Other);
 
+  /// Calls makeAllowedICmpRegion with a CmpPredicate, yielding an asymmetric
+  /// range when samesign information is present.
+  static ConstantRange makeAsymmetricICmpRegion(CmpPredicate Pred,
+                                                const ConstantRange &Other);
+
   /// Produce the largest range such that all values in the returned range
   /// satisfy the given predicate with all values contained within Other.
   /// Formally, this returns a subset of
diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index 3cbc4107433ef3d..939df1e4677bf2a 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -3012,7 +3012,7 @@ static Value *simplifyICmpWithConstant(CmpPredicate Pred, Value *LHS,
   }
 
   // Rule out tautological comparisons (eg., ult 0 or uge 0).
-  ConstantRange RHS_CR = ConstantRange::makeExactICmpRegion(Pred, *C);
+  ConstantRange RHS_CR = ConstantRange::makeAsymmetricICmpRegion(Pred, *C);
   if (RHS_CR.isEmptySet())
     return ConstantInt::getFalse(ITy);
   if (RHS_CR.isFullSet())
diff --git a/llvm/lib/IR/ConstantRange.cpp b/llvm/lib/IR/ConstantRange.cpp
index 35664353989929d..0728cbeac9e730f 100644
--- a/llvm/lib/IR/ConstantRange.cpp
+++ b/llvm/lib/IR/ConstantRange.cpp
@@ -145,6 +145,14 @@ ConstantRange ConstantRange::makeAllowedICmpRegion(CmpInst::Predicate Pred,
   }
 }
 
+ConstantRange ConstantRange::makeAsymmetricICmpRegion(CmpPredicate Pred,
+                                                      const ConstantRange &CR) {
+  if (Pred.hasSameSign() && ICmpInst::isRelational(Pred))
+    return makeAllowedICmpRegion(Pred, CR).unionWith(makeAllowedICmpRegion(
+        ICmpInst::getFlippedSignednessPredicate(Pred), CR));
+  return makeAllowedICmpRegion(Pred, CR);
+}
+
 ConstantRange ConstantRange::makeSatisfyingICmpRegion(CmpInst::Predicate Pred,
                                                       const ConstantRange &CR) {
   // Follows from De-Morgan's laws:
diff --git a/llvm/test/Analysis/ValueTracking/constant-ranges.ll b/llvm/test/Analysis/ValueTracking/constant-ranges.ll
index 7a4b9f7ed645a9f..2e9731895bff3ce 100644
--- a/llvm/test/Analysis/ValueTracking/constant-ranges.ll
+++ b/llvm/test/Analysis/ValueTracking/constant-ranges.ll
@@ -180,7 +180,7 @@ define i1 @srem_posC_okay1(i8 %x) {
 
 define i1 @srem_posC_okay1_samesign(i8 %x) {
 ; CHECK-LABEL: @srem_posC_okay1_samesign(
-; CHECK-NEXT:    ret i1 false
+; CHECK-NEXT:    ret i1 true
 ;
   %val = srem i8 34, %x
   %r = icmp samesign uge i8 %val, -3
@@ -198,9 +198,7 @@ define i1 @srem_negC_okay0(i8 %x) {
 
 define i1 @srem_negC_okay0_samesign(i8 %x) {
 ; CHECK-LABEL: @srem_negC_okay0_samesign(
-; CHECK-NEXT:    [[VAL:%.*]] = srem i8 -34, [[X:%.*]]
-; CHECK-NEXT:    [[R:%.*]] = icmp samesign ule i8 [[VAL]], 0
-; CHECK-NEXT:    ret i1 [[R]]
+; CHECK-NEXT:    ret i1 true
 ;
   %val = srem i8 -34, %x
   %r = icmp samesign ule i8 %val, 0
@@ -218,9 +216,7 @@ define i1 @srem_negC_okay1(i8 %x) {
 
 define i1 @srem_negC_okay1_samesign(i8 %x) {
 ; CHECK-LABEL: @srem_negC_okay1_samesign(
-; CHECK-NEXT:    [[VAL:%.*]] = srem i8 -34, [[X:%.*]]
-; CHECK-NEXT:    [[R:%.*]] = icmp samesign uge i8 [[VAL]], -34
-; CHECK-NEXT:    ret i1 [[R]]
+; CHECK-NEXT:    ret i1 true
 ;
   %val = srem i8 -34, %x
   %r = icmp samesign uge i8 %val, -34



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