Add a regression test for the bug exposed by r158087, which has been

temporarily reverted.

This test is annoyingly overspecified, but I don't know of another way
to thoroughly test the saving and restoring of the registers. While this
will have to be adjusted even with the issue fixed in order to re-apply
r158087, those adjustments should very clearly indicate that it is still
correct (%esp getting restored prior to pops), whereas without it, this
case can easily slip under the radar.

Still, any suggestions for improvements are very welcome.

All credit to Matt Beaumont-Gay for reducing this out of an insane
Address Sanitizer crash to a reasonably small seg-faulting C program
when built with -mstackrealign. I just reduced it to IR, which was much
simpler. =]

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@158656 91177308-0d34-0410-b5e6-96231b3b80d8

test/CodeGen/X86/force-align-stack-alloca.ll

@@ -0,0 +1,63 @@
+; This test is attempting to detect when we request forced re-alignment of the
+; stack to an alignment greater than would be available due to the ABI. We
+; arbitrarily force alignment up to 32-bytes for i386 hoping that this will
+; exceed any ABI provisions.
+;
+; RUN: llc < %s -force-align-stack -stack-alignment=32 | FileCheck %s
+
+target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:32:32-n8:16:32-S128"
+target triple = "i386-unknown-linux-gnu"
+
+define i32 @f(i8* %p) nounwind {
+entry:
+  %0 = load i8* %p
+  %conv = sext i8 %0 to i32
+  ret i32 %conv
+}
+
+define i64 @g(i32 %i) nounwind {
+; CHECK: g:
+; CHECK:      pushl
+; CHECK-NEXT: movl   %esp, %ebp
+; CHECK-NEXT: pushl
+; CHECK-NEXT: subl   $20, %esp
+; CHECK-NOT:         {{[^ ,]*}}, %esp
+;
+; The next adjustment of the stack is due to the alloca.
+; CHECK:      movl   %{{...}}, %esp
+; CHECK-NOT:         {{[^ ,]*}}, %esp
+;
+; Next we set up the memset call, and then undo it.
+; CHECK:      subl   $32, %esp
+; CHECK-NOT:         {{[^ ,]*}}, %esp
+; CHECK:      calll  memset
+; CHECK-NEXT: addl   $32, %esp
+; CHECK-NOT:         {{[^ ,]*}}, %esp
+;
+; Next we set up the call to 'f'.
+; CHECK:      subl   $32, %esp
+; CHECK-NOT:         {{[^ ,]*}}, %esp
+; CHECK:      calll  f
+; CHECK-NEXT: addl   $32, %esp
+; CHECK-NOT:         {{[^ ,]*}}, %esp
+;
+; Finally we nede to restore %esp from %ebp, the alloca prevents us from
+; restoring it directly.
+; CHECK-NOT:  popl
+; CHECK:      leal   -4(%ebp), %esp
+; CHECK-NEXT: popl
+; CHECK-NEXT: popl
+; CHECK-NEXT: ret
+
+entry:
+  br label %if.then
+
+if.then:
+  %0 = alloca i8, i32 %i
+  call void @llvm.memset.p0i8.i32(i8* %0, i8 0, i32 %i, i32 1, i1 false)
+  %call = call i32 @f(i8* %0)
+  %conv = sext i32 %call to i64
+  ret i64 %conv
+}
+
+declare void @llvm.memset.p0i8.i32(i8*, i8, i32, i32, i1) nounwind