[llvm] [InstCombine] Support multi-use values in cast elimination transforms (PR #165877)

[Yingwei Zheng via llvm-commits]

================
@@ -12,27 +12,41 @@
 
 #include "InstCombineInternal.h"
 #include "llvm/ADT/APInt.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/STLFunctionalExtras.h"
 #include "llvm/ADT/SetVector.h"
+#include "llvm/ADT/SmallVector.h"
 #include "llvm/Analysis/ConstantFolding.h"
 #include "llvm/IR/DataLayout.h"
 #include "llvm/IR/DebugInfo.h"
+#include "llvm/IR/Instruction.h"
 #include "llvm/IR/PatternMatch.h"
+#include "llvm/IR/Type.h"
 #include "llvm/IR/Value.h"
 #include "llvm/Support/KnownBits.h"
 #include "llvm/Transforms/InstCombine/InstCombiner.h"
+#include <iterator>
 #include <optional>
 
 using namespace llvm;
 using namespace PatternMatch;
 
 #define DEBUG_TYPE "instcombine"
 
-/// Given an expression that CanEvaluateTruncated or CanEvaluateSExtd returns
-/// true for, actually insert the code to evaluate the expression.
-Value *InstCombinerImpl::EvaluateInDifferentType(Value *V, Type *Ty,
-                                                 bool isSigned) {
+using EvaluatedMap = SmallDenseMap<Value *, Value *, 8>;
+
+static Value *EvaluateInDifferentTypeImpl(Value *V, Type *Ty, bool isSigned,
+                                          InstCombinerImpl &IC,
+                                          EvaluatedMap &Processed) {
+  // Since we cover transformation of isntructions with multiple users, we might
+  // come to the same node via multiple paths. We should not create a
+  // replacement for every single one of them though.
+  if (const auto It = Processed.find(V); It != Processed.end())
+    return It->getSecond();
----------------
dtcxzyw wrote:

```suggestion
  if (auto *Res = Processed.lookup())
    return Res;
```

https://github.com/llvm/llvm-project/pull/165877