[clang] [compiler-rt] [Clang][CodeGen] Report when an alias points to an incompatible target (PR #192397)

[Eli Friedman via cfe-commits]

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@@ -804,6 +804,49 @@ void CodeGenModule::checkAliases() {
       continue;
     }
 
+    if (!IsIFunc) {
+      GlobalDecl AliaseeGD;
+      lookupRepresentativeDecl(GV->getName(), AliaseeGD);
+      assert(AliaseeGD);
+      // Function declarations can only alias functions (including IFUNCs).
+      // Similarly, variable declarations can only alias variables.
+      if (isa<FunctionDecl>(D) != isa<llvm::Function, llvm::GlobalIFunc>(GV)) {
+        Diags.Report(Location, diag::err_alias_between_function_and_variable)
+            << isa<FunctionDecl>(D);
+        Diags.Report(AliaseeGD.getDecl()->getLocation(),
+                     diag::note_aliasee_declaration);
+        Error = true;
+        continue;
+      }
+
+      auto shouldReportTypeMismatch = [&]() {
+        QualType AliasQTy = D->getType().getCanonicalType();
+        QualType AliaseeQTy =
+            cast<ValueDecl>(AliaseeGD.getDecl())->getType().getCanonicalType();
+
+        // Same types, nothing to report.
+        if (AliasQTy == AliaseeQTy)
+          return false;
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efriedma-quic wrote:

Do we want to check for compatible types, instead of straight equality?  It doesn't make a big difference it most cases, but the compatible type infrastructure does handle FunctionNoProtoType for you.

https://github.com/llvm/llvm-project/pull/192397