[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, 10 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/ARM/tail-call.ll b/llvm/test/CodeGen/ARM/tail-call.ll
index 771158632ec..c3e79652c03 100644
--- a/llvm/test/CodeGen/ARM/tail-call.ll
+++ b/llvm/test/CodeGen/ARM/tail-call.ll
@@ -3,6 +3,7 @@
 ; RUN:   | FileCheck %s -check-prefix CHECK-NO-TAIL
 
 declare i32 @callee(i32 %i)
+declare extern_weak fastcc void @callee_weak()
 
 define i32 @caller(i32 %i) {
 entry:
@@ -19,3 +20,12 @@ entry:
 ; CHECK-NO-TAIL: pop {lr}
 ; CHECK-NO-TAIL: bx lr
 
+
+; 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
+}