Fix failure to invoke exception handler on Win64

When the last instruction prior to a function epilogue is a call, we
need to emit a nop so that the return address is not in the epilogue IP
range.  This is consistent with MSVC's behavior, and may be a workaround
for a bug in the Win64 unwinder.

Differential Revision: http://reviews.llvm.org/D4751

Patch by Vadim Chugunov!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214775 91177308-0d34-0410-b5e6-96231b3b80d8

test/CodeGen/X86/win64_call_epi.ll

@@ -0,0 +1,65 @@
+; RUN: llc < %s -mtriple=x86_64-pc-mingw32 | FileCheck %s -check-prefix=WIN64
+
+declare void @bar()
+declare void @baz()
+declare i32 @personality(...)
+
+; Check for 'nop' between the last call and the epilogue.
+define void @foo1() {
+
+    invoke void @bar()
+        to label %normal
+        unwind label %catch
+
+normal:
+    ret void
+
+catch:
+    %1 = landingpad { i8*, i32 } personality i32 (...)* @personality cleanup
+    resume { i8*, i32 } %1
+}
+; WIN64-LABEL: foo1:
+; WIN64: .seh_proc foo1
+; WIN64: callq bar
+; WIN64: nop
+; WIN64: addq ${{[0-9]+}}, %rsp
+; WIN64: retq
+; Check for 'ud2' after noreturn call
+; WIN64: callq _Unwind_Resume
+; WIN64-NEXT: ud2
+; WIN64: .seh_endproc
+
+
+; Check it still works when blocks are reordered.
+@something = global i32 0
+define void @foo2(i1 zeroext %cond ) {
+    br i1 %cond, label %a, label %b, !prof !0
+a:
+    call void @bar()
+    br label %done
+b:
+    call void @baz()
+    store i32 0, i32* @something
+    br label %done
+done:
+    ret void
+}
+!0 = metadata !{metadata !"branch_weights", i32 100, i32 0}
+; WIN64-LABEL: foo2:
+; WIN64: callq bar
+; WIN64: nop
+; WIN64: addq ${{[0-9]+}}, %rsp
+; WIN64: retq
+
+
+; Check nop is not emitted when call is not adjacent to epilogue.
+define i32 @foo3() {
+    call void @bar()
+    ret i32 0
+}
+; WIN64-LABEL: foo3:
+; WIN64: callq bar
+; WIN64: xorl
+; WIN64-NOT: nop
+; WIN64: addq ${{[0-9]+}}, %rsp
+; WIN64: retq