[llvm] IROutliner: Use ValueMapper to remap constants in a function (PR #134850)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm created https://github.com/llvm/llvm-project/pull/134850

Stop relying on the uselist of constants, which also required filtering
the uses that are in the correct function. I'm not sure why this pass is
doing its own cloning instead of building the value map while doing its
cloning.

>From 96a409796f4bea143f67109a72b9d49a33fe1554 Mon Sep 17 00:00:00 2001
From: Matt Arsenault <Matthew.Arsenault at amd.com>
Date: Tue, 8 Apr 2025 19:24:12 +0700
Subject: [PATCH] IROutliner: Use ValueMapper to remap constants in a function

Stop relying on the uselist of constants, which also required filtering
the uses that are in the correct function. I'm not sure why this pass is
doing its own cloning instead of building the value map while doing its
cloning.
---
 llvm/lib/Transforms/IPO/IROutliner.cpp | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/llvm/lib/Transforms/IPO/IROutliner.cpp b/llvm/lib/Transforms/IPO/IROutliner.cpp
index fd76d3a32049c..7e9ec4a04d5e3 100644
--- a/llvm/lib/Transforms/IPO/IROutliner.cpp
+++ b/llvm/lib/Transforms/IPO/IROutliner.cpp
@@ -24,6 +24,7 @@
 #include "llvm/IR/PassManager.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Transforms/IPO.h"
+#include "llvm/Transforms/Utils/ValueMapper.h"
 #include <optional>
 #include <vector>
 
@@ -1930,10 +1931,12 @@ replaceArgumentUses(OutlinableRegion &Region,
 /// \param Region [in] - The region of extracted code to be changed.
 void replaceConstants(OutlinableRegion &Region) {
   OutlinableGroup &Group = *Region.Parent;
+  Function *OutlinedFunction = Group.OutlinedFunction;
+  ValueToValueMapTy VMap;
+
   // Iterate over the constants that need to be elevated into arguments
   for (std::pair<unsigned, Constant *> &Const : Region.AggArgToConstant) {
     unsigned AggArgIdx = Const.first;
-    Function *OutlinedFunction = Group.OutlinedFunction;
     assert(OutlinedFunction && "Overall Function is not defined?");
     Constant *CST = Const.second;
     Argument *Arg = Group.OutlinedFunction->getArg(AggArgIdx);
@@ -1943,16 +1946,14 @@ void replaceConstants(OutlinableRegion &Region) {
     // TODO: If in the future constants do not have one global value number,
     // i.e. a constant 1 could be mapped to several values, this check will
     // have to be more strict.  It cannot be using only replaceUsesWithIf.
-
+    VMap[CST] = Arg;
     LLVM_DEBUG(dbgs() << "Replacing uses of constant " << *CST
                       << " in function " << *OutlinedFunction << " with "
-                      << *Arg << "\n");
-    CST->replaceUsesWithIf(Arg, [OutlinedFunction](Use &U) {
-      if (Instruction *I = dyn_cast<Instruction>(U.getUser()))
-        return I->getFunction() == OutlinedFunction;
-      return false;
-    });
+                      << *Arg << '\n');
   }
+
+  RemapFunction(*OutlinedFunction, VMap,
+                RF_NoModuleLevelChanges | RF_IgnoreMissingLocals);
 }
 
 /// It is possible that there is a basic block that already performs the same