[WIP][CFI][LTO] Avoid duplicate symbols on aliased weak function

[vitalybuka]

Problem is that LowerTypeTests expects that only one
definition will be left by LTO for a symbol.

However, thanks to strong alias, weak non-prevaling
definition can be preserved.

So strong and weak function definition will be renamed to strong .cfi,
making them duplicate.

Fixes #150070.

[llvmbot]

@llvm/pr-subscribers-llvm-transforms

Author: Vitaly Buka (vitalybuka)

Changes

Problem is that LowerTypeTests expects that only one
definition will be left by LTO for a symbol.

However, thanks to strong alias, weak non-prevaling
definition can be preserved.

So strong and weak function definition will be renamed to strong .cfi,
making them duplicate.

Fixes #150070.

---

Full diff: https://github.com/llvm/llvm-project/pull/150072.diff

1 Files Affected:

• (modified) llvm/lib/Transforms/IPO/LowerTypeTests.cpp (-1)

diff --git a/llvm/lib/Transforms/IPO/LowerTypeTests.cpp b/llvm/lib/Transforms/IPO/LowerTypeTests.cpp
index 486205c8a3848..71f827dd87086 100644
--- a/llvm/lib/Transforms/IPO/LowerTypeTests.cpp
+++ b/llvm/lib/Transforms/IPO/LowerTypeTests.cpp
@@ -1135,7 +1135,6 @@ void LowerTypeTestsModule::importFunction(
   } else {
     F->setName(Name + ".cfi");
     maybeReplaceComdat(F, Name);
-    F->setLinkage(GlobalValue::ExternalLinkage);
     FDecl = Function::Create(F->getFunctionType(), GlobalValue::ExternalLinkage,
                              F->getAddressSpace(), Name, &M);
     FDecl->setVisibility(Visibility);

[vitalybuka]

@pcc I believe even if this works it's wrong fix.

We probably should rather check if LTO have selected this definition as prevailing before renaming it into .cfi (or make it internal linkage it it's not)

WDYT?