[llvm] [IR] Add helper `CmpPredicate::withoutSameSign` (PR #134071)

[Yingwei Zheng via llvm-commits]

https://github.com/dtcxzyw created https://github.com/llvm/llvm-project/pull/134071

Address review comment https://github.com/llvm/llvm-project/pull/133711#discussion_r2024519641


>From 89632109521c70b9f138b8397455181389cc107b Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Wed, 2 Apr 2025 19:02:02 +0800
Subject: [PATCH] [IR] Add helper `CmpPredicate::withoutSameSign`

---
 llvm/include/llvm/IR/CmpPredicate.h                     | 4 ++++
 llvm/lib/Analysis/ScalarEvolution.cpp                   | 8 ++++----
 llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp | 2 +-
 3 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/llvm/include/llvm/IR/CmpPredicate.h b/llvm/include/llvm/IR/CmpPredicate.h
index 6921afbc58d25..62883a7365261 100644
--- a/llvm/include/llvm/IR/CmpPredicate.h
+++ b/llvm/include/llvm/IR/CmpPredicate.h
@@ -41,6 +41,10 @@ class CmpPredicate {
   /// Query samesign information, for optimizations.
   bool hasSameSign() const { return HasSameSign; }
 
+  /// Drops samesign information. This is used when the samesign information
+  /// should be dropped explicitly.
+  CmpInst::Predicate withoutSameSign() const { return Pred; }
+
   /// Compares two CmpPredicates taking samesign into account and returns the
   /// canonicalized CmpPredicate if they match. An alternative to operator==.
   ///
diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 2bf738cd16d65..dc74f480f12bb 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -11622,7 +11622,7 @@ bool ScalarEvolution::isBasicBlockEntryGuardedByCond(const BasicBlock *BB,
   // to prove non-equality and non-strict comparison separately.
   CmpPredicate NonStrictPredicate = ICmpInst::getNonStrictCmpPredicate(Pred);
   const bool ProvingStrictComparison =
-      (Pred != static_cast<CmpInst::Predicate>(NonStrictPredicate));
+      Pred != NonStrictPredicate.withoutSameSign();
   bool ProvedNonStrictComparison = false;
   bool ProvedNonEquality = false;
 
@@ -11792,9 +11792,9 @@ bool ScalarEvolution::isImpliedCond(CmpPredicate Pred, const SCEV *LHS,
         const SCEV *TruncFoundLHS = getTruncateExpr(FoundLHS, NarrowType);
         const SCEV *TruncFoundRHS = getTruncateExpr(FoundRHS, NarrowType);
         // We cannot preserve samesign after truncation.
-        if (isImpliedCondBalancedTypes(
-                Pred, LHS, RHS, static_cast<ICmpInst::Predicate>(FoundPred),
-                TruncFoundLHS, TruncFoundRHS, CtxI))
+        if (isImpliedCondBalancedTypes(Pred, LHS, RHS,
+                                       FoundPred.withoutSameSign(),
+                                       TruncFoundLHS, TruncFoundRHS, CtxI))
           return true;
       }
     }
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index e75b4026d5424..663c8a38f5876 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -5641,7 +5641,7 @@ Instruction *InstCombinerImpl::foldICmpWithMinMax(Instruction &I,
   // execute comparisons. For example, `icmp samesign ult umax(X, -46), -32`
   // cannot be decomposed into `(icmp samesign ult X, -46) or (icmp samesign ult
   // -46, -32)`. `X` is allowed to be non-negative here.
-  Pred = static_cast<CmpInst::Predicate>(Pred);
+  Pred = Pred.withoutSameSign();
   auto CmpXZ = IsCondKnownTrue(simplifyICmpInst(Pred, X, Z, Q));
   auto CmpYZ = IsCondKnownTrue(simplifyICmpInst(Pred, Y, Z, Q));
   if (!CmpXZ.has_value() && !CmpYZ.has_value())