[ARM,AArch64] Do not tail-call to an externally-defined function with weak linkage

Externally-defined functions with weak linkage should not be
tail-called on ARM or AArch64, as the AAELF spec requires normal calls
to undefined weak functions to be replaced with a NOP or jump to the
next instruction. The behaviour of branch instructions in this
situation (as used for tail calls) is implementation-defined, so we
cannot rely on the linker replacing the tail call with a return.

llvm-svn: 215890

1 files changed, 11 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/AArch64/tail-call.ll b/llvm/test/CodeGen/AArch64/tail-call.ll
index 8aab8421526..7fb39545a32 100644
--- a/llvm/test/CodeGen/AArch64/tail-call.ll
+++ b/llvm/test/CodeGen/AArch64/tail-call.ll
@@ -3,6 +3,7 @@
 declare fastcc void @callee_stack0()
 declare fastcc void @callee_stack8([8 x i32], i64)
 declare fastcc void @callee_stack16([8 x i32], i64, i64)
+declare extern_weak fastcc void @callee_weak()
 
 define fastcc void @caller_to0_from0() nounwind {
 ; CHECK-LABEL: caller_to0_from0:
@@ -92,3 +93,13 @@ define fastcc void @caller_to16_from16([8 x i32], i64 %a, i64 %b) {
 ; CHECK-NEXT: add sp, sp, #16
 ; CHECK-NEXT: b callee_stack16
 }
+
+
+; Weakly-referenced extern functions cannot be tail-called, as AAELF does
+; not define the behaviour of branch instructions to undefined weak symbols.
+define fastcc void @caller_weak() {
+; CHECK-LABEL: caller_weak:
+; CHECK: bl callee_weak
+  tail call void @callee_weak()
+  ret void
+}