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, 34 insertions, 0 deletions

diff --git a/test/CodeGen/Thumb2/2010-11-22-EpilogueBug.ll b/test/CodeGen/Thumb2/2010-11-22-EpilogueBug.ll
new file mode 100644
index 0000000000..313728c1b5
--- /dev/null
+++ b/test/CodeGen/Thumb2/2010-11-22-EpilogueBug.ll
@@ -0,0 +1,34 @@
+; rdar://8465407
+; RUN: llc < %s -mtriple=thumbv7-apple-darwin | FileCheck %s
+
+%struct.buf = type opaque
+
+declare void @bar() nounwind optsize
+
+define void @foo() nounwind optsize {
+; CHECK: foo:
+; CHECK: push
+; CHECK: add r7, sp, #4
+; CHECK: sub sp, #4
+entry:
+  %m.i = alloca %struct.buf*, align 4
+  br label %bb
+
+bb:
+  br i1 undef, label %bb3, label %bb2
+
+bb2:
+  call void @bar() nounwind optsize
+  br i1 undef, label %bb, label %bb3
+
+bb3:
+  br i1 undef, label %return, label %bb
+
+return:
+; CHECK: %return
+; 'mov sp, r7' would have left sp in an invalid state
+; CHECK-NOT: mov sp, r7
+; CHECK-NOT: sub, sp, #4
+; CHECK: add sp, #4
+  ret void
+}