Some ARM implementaions, e.g. A-series, does return stack prediction. That is,

the processor keeps a return addresses stack (RAS) which stores the address
and the instruction execution state of the instruction after a function-call
type branch instruction.

Calling a "noreturn" function with normal call instructions (e.g. bl) can
corrupt RAS and causes 100% return misprediction so LLVM should use a
unconditional branch instead. i.e.
mov lr, pc
b _foo
The "mov lr, pc" is issued in order to get proper backtrace.

rdar://8979299


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@151623 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 30 insertions, 0 deletions

diff --git a/test/CodeGen/ARM/call-noret.ll b/test/CodeGen/ARM/call-noret.ll
new file mode 100644
index 0000000000..c2ce079045
--- /dev/null
+++ b/test/CodeGen/ARM/call-noret.ll
@@ -0,0 +1,30 @@
+; RUN: llc < %s -mtriple=armv7-apple-ios -mcpu=cortex-a8   | FileCheck %s -check-prefix=ARM
+; RUN: llc < %s -mtriple=thumbv7-apple-ios -mcpu=cortex-a8 | FileCheck %s -check-prefix=T2
+; rdar://8979299
+
+define void @t1() noreturn nounwind ssp {
+entry:
+; ARM: t1:
+; ARM: mov lr, pc
+; ARM: b _bar
+
+; T2: t1:
+; T2: blx _bar
+  tail call void @bar() noreturn nounwind
+  unreachable
+}
+
+define void @t2() noreturn nounwind ssp {
+entry:
+; ARM: t2:
+; ARM: mov lr, pc
+; ARM: b _t1
+
+; T2: t2:
+; T2: mov lr, pc
+; T2: b.w _t1
+  tail call void @t1() noreturn nounwind
+  unreachable
+}
+
+declare void @bar() noreturn