[GlobalOpt] Don't replace the aliasee if it has other references.

As long as aliasee has `@llvm.used` or `@llvm.compiler.used` references, we cannot do the related replace or delete operations. Even if it is a Local Linkage, we cannot infer if there is no other use for it, such as asm or other future added cases.

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D145293

1 files changed, 7 insertions, 23 deletions

diff --git a/llvm/lib/Transforms/IPO/GlobalOpt.cpp b/llvm/lib/Transforms/IPO/GlobalOpt.cpp
index 4b6e8e3..50b9094 100644
--- a/llvm/lib/Transforms/IPO/GlobalOpt.cpp
+++ b/llvm/lib/Transforms/IPO/GlobalOpt.cpp
@@ -2219,22 +2219,11 @@ static bool hasUseOtherThanLLVMUsed(GlobalAlias &GA, const LLVMUsed &U) {
   return !U.usedCount(&GA) && !U.compilerUsedCount(&GA);
 }
 
-static bool hasMoreThanOneUseOtherThanLLVMUsed(GlobalValue &V,
-                                               const LLVMUsed &U) {
-  unsigned N = 2;
-  assert((!U.usedCount(&V) || !U.compilerUsedCount(&V)) &&
-         "We should have removed the duplicated "
-         "element from llvm.compiler.used");
-  if (U.usedCount(&V) || U.compilerUsedCount(&V))
-    ++N;
-  return V.hasNUsesOrMore(N);
-}
-
-static bool mayHaveOtherReferences(GlobalAlias &GA, const LLVMUsed &U) {
-  if (!GA.hasLocalLinkage())
+static bool mayHaveOtherReferences(GlobalValue &GV, const LLVMUsed &U) {
+  if (!GV.hasLocalLinkage())
     return true;
 
-  return U.usedCount(&GA) || U.compilerUsedCount(&GA);
+  return U.usedCount(&GV) || U.compilerUsedCount(&GV);
 }
 
 static bool hasUsesToReplace(GlobalAlias &GA, const LLVMUsed &U,
@@ -2248,21 +2237,16 @@ static bool hasUsesToReplace(GlobalAlias &GA, const LLVMUsed &U,
   if (!mayHaveOtherReferences(GA, U))
     return Ret;
 
-  // If the aliasee has internal linkage, give it the name and linkage
-  // of the alias, and delete the alias.  This turns:
+  // If the aliasee has internal linkage and no other references (e.g.,
+  // @llvm.used, @llvm.compiler.used), give it the name and linkage of the
+  // alias, and delete the alias. This turns:
   //   define internal ... @f(...)
   //   @a = alias ... @f
   // into:
   //   define ... @a(...)
   Constant *Aliasee = GA.getAliasee();
   GlobalValue *Target = cast<GlobalValue>(Aliasee->stripPointerCasts());
-  if (!Target->hasLocalLinkage())
-    return Ret;
-
-  // Do not perform the transform if multiple aliases potentially target the
-  // aliasee. This check also ensures that it is safe to replace the section
-  // and other attributes of the aliasee with those of the alias.
-  if (hasMoreThanOneUseOtherThanLLVMUsed(*Target, U))
+  if (mayHaveOtherReferences(*Target, U))
     return Ret;
 
   RenameTarget = true;