Make sure the non-SSE lowering for fences correctly clobbers EFLAGS. PR11768.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@148240 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/X86/X86InstrCompiler.td

@@ -551,7 +551,7 @@ def ATOMSWAP6432 : I<0, Pseudo, (outs GR32:$dst1, GR32:$dst2),
 // Memory barriers
 
 // TODO: Get this to fold the constant into the instruction.
-let isCodeGenOnly = 1 in
+let isCodeGenOnly = 1, Defs = [EFLAGS] in
 def OR32mrLocked  : I<0x09, MRMDestMem, (outs), (ins i32mem:$dst, GR32:$zero),
                       "lock\n\t"
                       "or{l}\t{$zero, $dst|$dst, $zero}",

test/CodeGen/X86/2012-01-16-mfence-nosse-flags.ll

@@ -0,0 +1,34 @@
+; RUN: llc < %s -mtriple=i686-linux -mattr=-sse | FileCheck %s
+; PR11768
+
+@ptr = external global i8*
+
+define void @baz() nounwind ssp {
+entry:
+  %0 = load i8** @ptr, align 4
+  %cmp = icmp eq i8* %0, null
+  fence seq_cst
+  br i1 %cmp, label %if.then, label %if.else
+
+; Make sure the fence comes before the comparison, since it
+; clobbers EFLAGS.
+
+; CHECK: lock
+; CHECK-NEXT: orl {{.*}}, (%esp)
+; CHECK-NEXT: cmpl $0
+
+if.then:                                          ; preds = %entry
+  tail call void bitcast (void (...)* @foo to void ()*)() nounwind
+  br label %if.end
+
+if.else:                                          ; preds = %entry
+  tail call void bitcast (void (...)* @bar to void ()*)() nounwind
+  br label %if.end
+
+if.end:                                           ; preds = %if.else, %if.then
+  ret void
+}
+
+declare void @foo(...)
+
+declare void @bar(...)