Fix epilogue codegen to avoid leaving the stack pointer in an invalid

state. Previously Thumb2 would restore sp from fp like this:
mov sp, r7
sub, sp, #4
If an interrupt is taken after the 'mov' but before the 'sub', callee-saved
registers might be clobbered by the interrupt handler. Instead, try
restoring directly from sp:
add sp, #4
Or, if necessary (with VLA, etc.) use a scratch register to compute sp and
then restore it:
sub.w r4, r7, #8
mov sp, r7
rdar://8465407


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@119977 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 9 insertions, 3 deletions

diff --git a/test/CodeGen/Thumb2/2010-08-10-VarSizedAllocaBug.ll b/test/CodeGen/Thumb2/2010-08-10-VarSizedAllocaBug.ll
index abcf13a..41f7f29 100644
--- a/test/CodeGen/Thumb2/2010-08-10-VarSizedAllocaBug.ll
+++ b/test/CodeGen/Thumb2/2010-08-10-VarSizedAllocaBug.ll
@@ -5,6 +5,10 @@
 define internal fastcc i32 @Callee(i32 %i) nounwind {
 entry:
 ; CHECK: Callee:
+; CHECK: push
+; CHECK: mov r4, sp
+; CHECK: sub.w r12, r4, #1000
+; CHECK: mov sp, r12
   %0 = icmp eq i32 %i, 0                          ; <i1> [#uses=1]
   br i1 %0, label %bb2, label %bb
 
@@ -17,9 +21,11 @@ bb:                                               ; preds = %entry
   ret i32 %4
 
 bb2:                                              ; preds = %entry
-; Must restore sp from fp here
-; CHECK: mov sp, r7
-; CHECK: sub sp, #8
+; Must restore sp from fp here. Make sure not to leave sp in a temporarily invalid
+; state though. rdar://8465407
+; CHECK-NOT: mov sp, r7
+; CHECK: sub.w r4, r7, #8
+; CHECK: mov sp, r4
 ; CHECK: pop
   ret i32 0
 }