[X86] Fix MCNullStreamer support for modules with a CodeView flag

[eush]

Summary

This fixes -filetype=null support when compiling for a Win32 target
and the module has a CodeView flag.

The only places changed are the uses of getTargetStreamer function -
this patch guards both of them with null checks.

[RKSimon]

lib/Target/X86/X86AsmPrinter.cpp

92

(style) We normally do auto for cast cases like this as the type is obvious.

104

(style) We normally do auto for cast cases like this as the type is obvious.

[eush]

Fixed style.

[RKSimon]

LGTM

[eush]

Could you commit this patch on my behalf?

lib/Target/X86/X86AsmPrinter.cpp

bool X86AsmPrinter::runOnMachineFunction(MachineFunction &MF) {
 
   // We didn't modify anything.
   return false;
 }
 
 void X86AsmPrinter::EmitFunctionBodyStart() {
   if (EmitFPOData) {
     X86TargetStreamer *XTS =
         static_cast<X86TargetStreamer *>(OutStreamer->getTargetStreamer());
     unsigned ParamsSize =
         MF->getInfo<X86MachineFunctionInfo>()->getArgumentStackSize();
+
+    if (XTS)
       XTS->emitFPOProc(CurrentFnSym, ParamsSize);
   }
 }
 
 void X86AsmPrinter::EmitFunctionBodyEnd() {
   if (EmitFPOData) {
-    X86TargetStreamer *XTS =
-        static_cast<X86TargetStreamer *>(OutStreamer->getTargetStreamer());
+    if (X86TargetStreamer *XTS =
+            static_cast<X86TargetStreamer *>(OutStreamer->getTargetStreamer()))
       XTS->emitFPOEndProc();
   }
 }
 
 /// printSymbolOperand - Print a raw symbol reference operand.  This handles
 /// jump tables, constant pools, global address and external symbols, all of
 /// which print to a label with various suffixes for relocation types etc.
 static void printSymbolOperand(X86AsmPrinter &P, const MachineOperand &MO,
                                raw_ostream &O) {

test/CodeGen/X86/null-streamer.ll

 ; Check the MCNullStreamer operates correctly, at least on a minimal test case.
 ;
 ; RUN: llc -filetype=null -o %t -mtriple=i686-- %s
 ; RUN: llc -filetype=null -o %t -mtriple=i686-cygwin %s
 
 source_filename = "test/CodeGen/X86/null-streamer.ll"
 
 define void @f0() {
   ret void
 }
 
 define void @f1() {
   ret void
 }
 
 !llvm.dbg.cu = !{!0}
-!llvm.module.flags = !{!7, !8}
+!llvm.module.flags = !{!7, !8, !9}
 
 !0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: " ", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, retainedTypes: !2, globals: !3, imports: !2)
 !1 = !DIFile(filename: "file.c", directory: "")
 !2 = !{}
 !3 = !{!4}
 !4 = !DIGlobalVariableExpression(var: !5, expr: !DIExpression())
 !5 = !DIGlobalVariable(name: "i", linkageName: "_ZL1i", scope: null, file: !1, line: 1, type: !6, isLocal: true, isDefinition: true)
 !6 = !DIBasicType(size: 32, align: 32, encoding: DW_ATE_signed)
 !7 = !{i32 2, !"Dwarf Version", i32 3}
 !8 = !{i32 1, !"Debug Info Version", i32 3}
-
+!9 = !{i32 2, !"CodeView", i32 1}