[llvm] 4bf67cd - [DenseMap] Fix constness issues with lookup_or (#139247)

[via llvm-commits]

Author: Ramkumar Ramachandra
Date: 2025-05-28T20:32:31+02:00
New Revision: 4bf67cdf026478c4bc3e708153c02f82e2c22524

URL: https://github.com/llvm/llvm-project/commit/4bf67cdf026478c4bc3e708153c02f82e2c22524
DIFF: https://github.com/llvm/llvm-project/commit/4bf67cdf026478c4bc3e708153c02f82e2c22524.diff

LOG: [DenseMap] Fix constness issues with lookup_or (#139247)

Also demonstrate its use in ScalarEvolution.

Added: 
    

Modified: 
    llvm/include/llvm/ADT/DenseMap.h
    llvm/lib/Analysis/ScalarEvolution.cpp
    llvm/unittests/ADT/DenseMapTest.cpp

Removed: 
    


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diff  --git a/llvm/include/llvm/ADT/DenseMap.h b/llvm/include/llvm/ADT/DenseMap.h
index 4df50e03de94b..de41a212c65ab 100644
--- a/llvm/include/llvm/ADT/DenseMap.h
+++ b/llvm/include/llvm/ADT/DenseMap.h
@@ -220,8 +220,7 @@ class DenseMapBase : public DebugEpochBase {
   // Return the entry with the specified key, or \p Default. This variant is
   // useful, because `lookup` cannot be used with non-default-constructible
   // values.
-  ValueT lookup_or(const_arg_type_t<KeyT> Val,
-                   const_arg_type_t<ValueT> Default) const {
+  ValueT lookup_or(const_arg_type_t<KeyT> Val, ValueT &&Default) const {
     if (const BucketT *Bucket = doFind(Val))
       return Bucket->getSecond();
     return Default;

diff  --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 4bd5a4c3ab75c..56cdfabccb66f 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -15904,10 +15904,7 @@ const SCEV *ScalarEvolution::LoopGuards::rewrite(const SCEV *Expr) const {
     const SCEV *visitAddRecExpr(const SCEVAddRecExpr *Expr) { return Expr; }
 
     const SCEV *visitUnknown(const SCEVUnknown *Expr) {
-      auto I = Map.find(Expr);
-      if (I == Map.end())
-        return Expr;
-      return I->second;
+      return Map.lookup_or(Expr, Expr);
     }
 
     const SCEV *visitZeroExtendExpr(const SCEVZeroExtendExpr *Expr) {

diff  --git a/llvm/unittests/ADT/DenseMapTest.cpp b/llvm/unittests/ADT/DenseMapTest.cpp
index d002a3c15cf52..c95f96c4bb3c6 100644
--- a/llvm/unittests/ADT/DenseMapTest.cpp
+++ b/llvm/unittests/ADT/DenseMapTest.cpp
@@ -671,6 +671,13 @@ TEST(DenseMapCustomTest, LookupOr) {
   EXPECT_EQ(M.lookup_or(2, 4u), 4u);
 }
 
+TEST(DenseMapCustomTest, LookupOrConstness) {
+  DenseMap<int, unsigned *> M;
+  unsigned Default = 3u;
+  unsigned *Ret = M.lookup_or(0, &Default);
+  EXPECT_EQ(Ret, &Default);
+}
+
 // Key traits that allows lookup with either an unsigned or char* key;
 // In the latter case, "a" == 0, "b" == 1 and so on.
 struct TestDenseMapInfo {