[llvm] [SCEV] Improve code in SCEVLoopGuardRewriter (NFC) (PR #139257)

[Ramkumar Ramachandra via llvm-commits]

https://github.com/artagnon updated https://github.com/llvm/llvm-project/pull/139257

>From 95dc5b8bc77128fd985b80b50ef887bf56764dfb Mon Sep 17 00:00:00 2001
From: Ramkumar Ramachandra <ramkumar.ramachandra at codasip.com>
Date: Fri, 9 May 2025 13:54:12 +0100
Subject: [PATCH 1/2] [SCEV] Improve code in SCEVLoopGuardRewriter (NFC)

Prefer DenseMap::lookup over DenseMap::find.
---
 llvm/lib/Analysis/ScalarEvolution.cpp | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 3f9614254ae7a..38071c0714e82 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -15867,8 +15867,8 @@ const SCEV *ScalarEvolution::LoopGuards::rewrite(const SCEV *Expr) const {
     }
 
     const SCEV *visitZeroExtendExpr(const SCEVZeroExtendExpr *Expr) {
-      auto I = Map.find(Expr);
-      if (I == Map.end()) {
+      const SCEV *S = Map.lookup(Expr);
+      if (!S) {
         // If we didn't find the extact ZExt expr in the map, check if there's
         // an entry for a smaller ZExt we can use instead.
         Type *Ty = Expr->getType();
@@ -15887,29 +15887,29 @@ const SCEV *ScalarEvolution::LoopGuards::rewrite(const SCEV *Expr) const {
         return SCEVRewriteVisitor<SCEVLoopGuardRewriter>::visitZeroExtendExpr(
             Expr);
       }
-      return I->second;
+      return S;
     }
 
     const SCEV *visitSignExtendExpr(const SCEVSignExtendExpr *Expr) {
-      auto I = Map.find(Expr);
-      if (I == Map.end())
+      const SCEV *S = Map.lookup(Expr);
+      if (!S)
         return SCEVRewriteVisitor<SCEVLoopGuardRewriter>::visitSignExtendExpr(
             Expr);
-      return I->second;
+      return S;
     }
 
     const SCEV *visitUMinExpr(const SCEVUMinExpr *Expr) {
-      auto I = Map.find(Expr);
-      if (I == Map.end())
+      const SCEV *S = Map.lookup(Expr);
+      if (!S)
         return SCEVRewriteVisitor<SCEVLoopGuardRewriter>::visitUMinExpr(Expr);
-      return I->second;
+      return S;
     }
 
     const SCEV *visitSMinExpr(const SCEVSMinExpr *Expr) {
-      auto I = Map.find(Expr);
-      if (I == Map.end())
+      const SCEV *S = Map.lookup(Expr);
+      if (!S)
         return SCEVRewriteVisitor<SCEVLoopGuardRewriter>::visitSMinExpr(Expr);
-      return I->second;
+      return S;
     }
 
     const SCEV *visitAddExpr(const SCEVAddExpr *Expr) {

>From 1d6841ae7b51edcc65a101ebc9bc4bfbfc9adcdb Mon Sep 17 00:00:00 2001
From: Ramkumar Ramachandra <ramkumar.ramachandra at codasip.com>
Date: Sun, 11 May 2025 10:43:29 +0100
Subject: [PATCH 2/2] [SCEV] Fix nit

---
 llvm/lib/Analysis/ScalarEvolution.cpp | 60 +++++++++++++--------------
 1 file changed, 28 insertions(+), 32 deletions(-)

diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 38071c0714e82..69714a112310e 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -15867,49 +15867,45 @@ const SCEV *ScalarEvolution::LoopGuards::rewrite(const SCEV *Expr) const {
     }
 
     const SCEV *visitZeroExtendExpr(const SCEVZeroExtendExpr *Expr) {
-      const SCEV *S = Map.lookup(Expr);
-      if (!S) {
-        // If we didn't find the extact ZExt expr in the map, check if there's
-        // an entry for a smaller ZExt we can use instead.
-        Type *Ty = Expr->getType();
-        const SCEV *Op = Expr->getOperand(0);
-        unsigned Bitwidth = Ty->getScalarSizeInBits() / 2;
-        while (Bitwidth % 8 == 0 && Bitwidth >= 8 &&
-               Bitwidth > Op->getType()->getScalarSizeInBits()) {
-          Type *NarrowTy = IntegerType::get(SE.getContext(), Bitwidth);
-          auto *NarrowExt = SE.getZeroExtendExpr(Op, NarrowTy);
-          auto I = Map.find(NarrowExt);
-          if (I != Map.end())
-            return SE.getZeroExtendExpr(I->second, Ty);
-          Bitwidth = Bitwidth / 2;
-        }
+      if (const SCEV *S = Map.lookup(Expr))
+        return S;
 
-        return SCEVRewriteVisitor<SCEVLoopGuardRewriter>::visitZeroExtendExpr(
-            Expr);
+      // If we didn't find the extact ZExt expr in the map, check if there's
+      // an entry for a smaller ZExt we can use instead.
+      Type *Ty = Expr->getType();
+      const SCEV *Op = Expr->getOperand(0);
+      unsigned Bitwidth = Ty->getScalarSizeInBits() / 2;
+      while (Bitwidth % 8 == 0 && Bitwidth >= 8 &&
+             Bitwidth > Op->getType()->getScalarSizeInBits()) {
+        Type *NarrowTy = IntegerType::get(SE.getContext(), Bitwidth);
+        auto *NarrowExt = SE.getZeroExtendExpr(Op, NarrowTy);
+        auto I = Map.find(NarrowExt);
+        if (I != Map.end())
+          return SE.getZeroExtendExpr(I->second, Ty);
+        Bitwidth = Bitwidth / 2;
       }
-      return S;
+
+      return SCEVRewriteVisitor<SCEVLoopGuardRewriter>::visitZeroExtendExpr(
+          Expr);
     }
 
     const SCEV *visitSignExtendExpr(const SCEVSignExtendExpr *Expr) {
-      const SCEV *S = Map.lookup(Expr);
-      if (!S)
-        return SCEVRewriteVisitor<SCEVLoopGuardRewriter>::visitSignExtendExpr(
-            Expr);
-      return S;
+      if (const SCEV *S = Map.lookup(Expr))
+        return S;
+      return SCEVRewriteVisitor<SCEVLoopGuardRewriter>::visitSignExtendExpr(
+          Expr);
     }
 
     const SCEV *visitUMinExpr(const SCEVUMinExpr *Expr) {
-      const SCEV *S = Map.lookup(Expr);
-      if (!S)
-        return SCEVRewriteVisitor<SCEVLoopGuardRewriter>::visitUMinExpr(Expr);
-      return S;
+      if (const SCEV *S = Map.lookup(Expr))
+        return S;
+      return SCEVRewriteVisitor<SCEVLoopGuardRewriter>::visitUMinExpr(Expr);
     }
 
     const SCEV *visitSMinExpr(const SCEVSMinExpr *Expr) {
-      const SCEV *S = Map.lookup(Expr);
-      if (!S)
-        return SCEVRewriteVisitor<SCEVLoopGuardRewriter>::visitSMinExpr(Expr);
-      return S;
+      if (const SCEV *S = Map.lookup(Expr))
+        return S;
+      return SCEVRewriteVisitor<SCEVLoopGuardRewriter>::visitSMinExpr(Expr);
     }
 
     const SCEV *visitAddExpr(const SCEVAddExpr *Expr) {