[LowerTypeTests] Discard extern_weak linkage for definitions

[vlad.tsyrklevich]

Summary

Fix PR37625. It's possible for an extern_weak declaration to be emitted
to the merged module when a definition exists in the ThinLTO portion of
the build; discard the linkage on the declaration in that case.
(otherwise we copy the linkage to the alias to the jumptable and fail)

[pcc]

LGTM

lib/Transforms/IPO/LowerTypeTests.cpp

if (CfiFunctionsMD) {
         // following the code path below to replace the type metadata.
         if (F->hasAvailableExternallyLinkage()) {
           F->setLinkage(GlobalValue::ExternalLinkage);
           F->deleteBody();
           F->setComdat(nullptr);
           F->clearMetadata();
         }
 
+        // Update the linkage for extern_weak declarations when a definition
+        // exists.
+        if (Linkage == CFL_Definition && F->hasExternalWeakLinkage())
+          F->setLinkage(GlobalValue::ExternalLinkage);
+
         // If the function in the full LTO module is a declaration, replace its
         // type metadata with the type metadata we found in cfi.functions. That
         // metadata is presumed to be more accurate than the metadata attached
         // to the declaration.
         if (F->isDeclaration()) {
           if (Linkage == CFL_WeakDeclaration)
             F->setLinkage(GlobalValue::ExternalWeakLinkage);
 

test/Transforms/LowerTypeTests/pr37625.ll

+; RUN: opt -S -lowertypetests -lowertypetests-summary-action=export -lowertypetests-read-summary=%S/Inputs/use-typeid1-typeid2.yaml -lowertypetests-write-summary=%t < %s | FileCheck %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+declare !type !2 extern_weak void @h(i8)
+
+!cfi.functions = !{!0, !1}
+
+!0 = !{!"h", i8 2, !2}
+!1 = !{!"h", i8 0, !2}
+!2 = !{i64 0, !"typeid1"}
+
+; CHECK-DAG: @h = alias void (i8), bitcast