[AVR] Support aliases in non-zero address space

[aykevl]

Summary

This fixes code like the following on AVR:

void foo(void) {
}
void bar(void) __attribute__((alias("foo")));

Code like this is present in compiler-rt, which I'm trying to build.

---

I'm not sure how to add a test for this, are there any examples I can look at? And does this need a test at all, considering how trivial the change is?

[dylanmckay]

I think we should add a test, it shouldn't be too hard I think.

Look in clang/tests, grep for alias. Look like it is extern const int __mod_usb_device_table __attribute__ ((alias("wacom_usb_ids")));. If you copy paste a new test (use clang/test/CodeGen/alias.c as a reference. You can also look for files with avr in the name under the test folder to see how to add an AVR-specific test.

You should be able to 1) define a function alias of another function and 2) CHECK that the final IR has address space attributes, even when the alias symbol is used instead of the original symbol.

[dylanmckay]

Nice patch by the way, the code looks fine, if we can get a basic test in here then it's good to go

[rjmccall]

I agree this needs a test case.

clang/lib/CodeGen/CodeGenModule.cpp

4550

Aliasee->getType()->getPointerAddressSpace()

LGTM. If we ever allow functions to declare an explicit address space, we'll need semantic checks that aliases match up, but that's okay.

[aykevl]

• added test
• using getPointerAddressSpace instead of a cast

This is now ready for review.

[rjmccall]

Thanks.

clang/lib/CodeGen/CodeGenModule.cpp

if (isa<llvm::FunctionType>(DeclTy)) {
     Aliasee = GetOrCreateLLVMGlobal(AA->getAliasee(),
                                     llvm::PointerType::getUnqual(DeclTy),
                                     /*D=*/nullptr);
     LT = getLLVMLinkageVarDefinition(cast<VarDecl>(GD.getDecl()),
                                      D->getType().isConstQualified());
   }
 
   // Create the new alias itself, but don't set a name yet.
+  unsigned AS = Aliasee->getType()->getPointerAddressSpace();
   auto *GA =
-      llvm::GlobalAlias::create(DeclTy, 0, LT, "", Aliasee, &getModule());
+      llvm::GlobalAlias::create(DeclTy, AS, LT, "", Aliasee, &getModule());
 
   if (Entry) {
     if (GA->getAliasee() == Entry) {
       Diags.Report(AA->getLocation(), diag::err_cyclic_alias) << 0;
       return;
     }
 
     assert(Entry->isDeclaration());
 
     // If there is a declaration in the module, then we had an extern followed
     // by the alias, as in:
     //   extern int test6();
     //   ...
     //   int test6() __attribute__((alias("test7")));
     //
     // Remove it and replace uses of it with the alias.
     GA->takeName(Entry);

clang/test/CodeGen/alias-avr.c

+// RUN: %clang_cc1 -triple avr-unknown-unknown -emit-llvm -o - %s | FileCheck %s
+
+int mul(int a, int b) {
+  return a * b;
+}
+
+// CHECK: @multiply = alias i16 (i16, i16), i16 (i16, i16) addrspace(1)* @mul
+int multiply(int x, int y) __attribute__((alias("mul")));