GlobalDCE: Delete available_externally initializers if it allows removing the value the initializer is referring to.

This is useful for functions that are not actually available externally but
referenced by a vtable of some kind. Clang emits functions like this for the MS
ABI.

PR20182.

llvm-svn: 212337

1 files changed, 34 insertions, 1 deletions

diff --git a/llvm/test/Transforms/GlobalDCE/externally_available.ll b/llvm/test/Transforms/GlobalDCE/externally_available.ll
index cc88cb10dcc..3dbada841f9 100644
--- a/llvm/test/Transforms/GlobalDCE/externally_available.ll
+++ b/llvm/test/Transforms/GlobalDCE/externally_available.ll
@@ -1,10 +1,43 @@
-; RUN: opt < %s -globaldce -S | not grep test_
+; RUN: opt < %s -globaldce -S | FileCheck %s
 
 ; test_function should not be emitted to the .s file.
+; CHECK-NOT: @test_function
 define available_externally i32 @test_function() {
   ret i32 4
 }
 
 ; test_global should not be emitted to the .s file.
+; CHECK-NOT: @test_global
 @test_global = available_externally global i32 4
 
+; CHECK: @x = external constant void ()*
+@x = available_externally constant void()* @f
+; CHECK: @y = external constant i32
+@y = available_externally constant i32 ptrtoint (void()* @g to i32)
+; @h is still alive, so don't remove the initializer too eagerly.
+; CHECK: @z = available_externally constant i8 ptrtoint (void (i8)* @h to i8)
+@z = available_externally constant i8 ptrtoint (void(i8)* @h to i8)
+
+; CHECK-NOT: @f
+define linkonce_odr void @f() {
+  ret void
+}
+
+; CHECK-NOT: @g
+define linkonce_odr void @g() {
+  ret void
+}
+
+; CHECK: define linkonce_odr void @h
+define linkonce_odr void @h(i8) {
+  ret void
+}
+
+define i32 @main() {
+  %f = load void()** @x
+  call void %f()
+  %g = load i32* @y
+  %h = load i8* @z
+  call void @h(i8 %h)
+  ret i32 %g
+}