Prevent alias from pointing to weak aliases.

This adds back r204781.

Original message:

Aliases are just another name for a position in a file. As such, the
regular symbol resolutions are not applied. For example, given

define void @my_func() {
  ret void
}
@my_alias = alias weak void ()* @my_func
@my_alias2 = alias void ()* @my_alias

We produce without this patch:

        .weak   my_alias
my_alias = my_func
        .globl  my_alias2
my_alias2 = my_alias

That is, in the resulting ELF file my_alias, my_func and my_alias are
just 3 names pointing to offset 0 of .text. That is *not* the
semantics of IR linking. For example, linking in a

@my_alias = alias void ()* @other_func

would require the strong my_alias to override the weak one and
my_alias2 would end up pointing to other_func.

There is no way to represent that with aliases being just another
name, so the best solution seems to be to just disallow it, converting
a miscompile into an error.

llvm-svn: 204934

4 files changed, 13 insertions, 8 deletions

diff --git a/llvm/test/CodeGen/X86/dllexport-x86_64.ll b/llvm/test/CodeGen/X86/dllexport-x86_64.ll
index 1fadfec2543..a38c2d8f8ab 100644
--- a/llvm/test/CodeGen/X86/dllexport-x86_64.ll
+++ b/llvm/test/CodeGen/X86/dllexport-x86_64.ll
@@ -65,7 +65,7 @@ define weak_odr dllexport void @weak1() {
 @alias2 = dllexport alias void()* @f1
 
 ; CHECK: .globl alias3
-; CHECK: alias3 = alias
+; CHECK: alias3 = notExported
 @alias3 = dllexport alias void()* @alias
 
 ; CHECK: .weak weak_alias
diff --git a/llvm/test/CodeGen/X86/dllexport.ll b/llvm/test/CodeGen/X86/dllexport.ll
index 7f0dadb6a2e..1b34d238693 100644
--- a/llvm/test/CodeGen/X86/dllexport.ll
+++ b/llvm/test/CodeGen/X86/dllexport.ll
@@ -80,7 +80,7 @@ define weak_odr dllexport void @weak1() {
 @alias2 = dllexport alias void()* @f1
 
 ; CHECK: .globl _alias3
-; CHECK: _alias3 = _alias
+; CHECK: _alias3 = _notExported
 @alias3 = dllexport alias void()* @alias
 
 ; CHECK: .weak _weak_alias
diff --git a/llvm/test/Feature/aliases.ll b/llvm/test/Feature/aliases.ll
index 7ffa5f26013..7fe9d0b374e 100644
--- a/llvm/test/Feature/aliases.ll
+++ b/llvm/test/Feature/aliases.ll
@@ -14,7 +14,7 @@
 define i32 @foo_f() {
   ret i32 0
 }
-@bar_f = alias weak %FunTy* @foo_f
+@bar_f = alias weak_odr %FunTy* @foo_f
 @bar_ff = alias i32()* @bar_f
 
 @bar_i = alias internal i32* @bar
diff --git a/llvm/test/Transforms/GlobalOpt/alias-resolve.ll b/llvm/test/Transforms/GlobalOpt/alias-resolve.ll
index 64e3d88af8a..2d5a956d14b 100644
--- a/llvm/test/Transforms/GlobalOpt/alias-resolve.ll
+++ b/llvm/test/Transforms/GlobalOpt/alias-resolve.ll
@@ -1,14 +1,17 @@
 ; RUN: opt < %s -globalopt -S | FileCheck %s
 
 @foo1 = alias void ()* @foo2
-; CHECK: @foo1 = alias void ()* @foo2
+; CHECK: @foo1 = alias void ()* @bar2
 
-@foo2 = alias weak void()* @bar1
-; CHECK: @foo2 = alias weak void ()* @bar2
+@foo2 = alias void()* @bar1
+; CHECK: @foo2 = alias void ()* @bar2
 
 @bar1  = alias void ()* @bar2
 ; CHECK: @bar1 = alias void ()* @bar2
 
+@weak1 = alias weak void ()* @bar2
+; CHECK: @weak1 = alias weak void ()* @bar2
+
 define void @bar2() {
   ret void
 }
@@ -17,14 +20,16 @@ define void @bar2() {
 define void @baz() {
 entry:
          call void @foo1()
-; CHECK: call void @foo2()
+; CHECK: call void @bar2()
 
          call void @foo2()
-; CHECK: call void @foo2()
+; CHECK: call void @bar2()
 
          call void @bar1()
 ; CHECK: call void @bar2()
 
+         call void @weak1()
+; CHECK: call void @weak1()
          ret void
 }