Fix verifier for GlobalAliases to avoid recursing into global initial…

…izers.

The verifier follows GlobalAlias operands so that it can detect cycles of
alias definitions. It was doing this in a way that caused it to also recurse
through initializers for the GlobalValue aliasees, and it would fail when
an initializer refers to a global that is a declaration and not a definition.
This patch causes it to stop recursing when it hits a global definition.
<rdar://problem/17277451>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210734 91177308-0d34-0410-b5e6-96231b3b80d8

lib/IR/Verifier.cpp

@@ -493,6 +493,10 @@ void Verifier::visitAliaseeSubExpr(SmallPtrSet<const GlobalAlias *, 4> &Visited,
 
       Assert1(!GA2->mayBeOverridden(), "Alias cannot point to a weak alias",
               &GA);
+    } else {
+      // Only continue verifying subexpressions of GlobalAliases.
+      // Do not recurse into global initializers.
+      return;
     }
   }
 

test/Verifier/alias.ll

@@ -11,6 +11,10 @@ declare void @f()
 ; CHECK: Alias must point to a definition
 ; CHECK-NEXT: @ga
 
+; References to a global declaration from an initializer are OK.
+@gptr = global i32* @g
+@gptr_a = alias i32** @gptr
+; CHECK-NOT: Alias must point to a definition
 
 @test2_a = alias i32* @test2_b
 @test2_b = alias i32* @test2_a