[X86] MOVPC32r should only emit CFI adjustments when needed

[mkuper]

Summary

Trying to emit CFI adjustments for MOVPC32r caused failures under windows.
Since we're so late in the pipeline here, I think the right thing to do is not to "guess" whether we should be emitting DWARF or not, but just check directly.

This fixes PR25828.

[rnk]

lgtm

lib/Target/X86/X86MCInstLower.cpp

case X86::MOVPC32r: {
     EmitAndCountInstruction(MCInstBuilder(X86::CALLpcrel32)
       .addExpr(MCSymbolRefExpr::create(PICBase, OutContext)));
 
     const X86FrameLowering* FrameLowering =
         MF->getSubtarget<X86Subtarget>().getFrameLowering();
     bool hasFP = FrameLowering->hasFP(*MF);
     
     // TODO: This is needed only if we require precise CFA.
-    bool NeedsDwarfCFI = 
-         (MMI->hasDebugInfo() || MF->getFunction()->needsUnwindTableEntry());
+    bool HasActiveDwarfFrame = OutStreamer->getNumFrameInfos() &&
+                               !OutStreamer->getDwarfFrameInfos().back().End;
+
     int stackGrowth = -RI->getSlotSize();
 
-    if (NeedsDwarfCFI && !hasFP) {
+    if (HasActiveDwarfFrame && !hasFP) {
       OutStreamer->EmitCFIAdjustCfaOffset(-stackGrowth);
     }
 
     // Emit the label.
     OutStreamer->EmitLabel(PICBase);
 
     // popl $reg
     EmitAndCountInstruction(MCInstBuilder(X86::POP32r)
                             .addReg(MI->getOperand(0).getReg()));
 
-    if (NeedsDwarfCFI && !hasFP) {
+    if (HasActiveDwarfFrame && !hasFP) {
       OutStreamer->EmitCFIAdjustCfaOffset(stackGrowth);
     }
     return;
   }
 
   case X86::ADD32ri: {
     // Lower the MO_GOT_ABSOLUTE_ADDRESS form of ADD32ri.
     if (MI->getOperand(2).getTargetFlags() != X86II::MO_GOT_ABSOLUTE_ADDRESS)

test/CodeGen/X86/pr25828.ll

+; RUN: llc < %s -mtriple=i686-pc-windows-msvc -relocation-model=pic | FileCheck %s
+; MOVPC32r should not generate CFI under windows
+
+; CHECK-LABEL: _foo:
+; CHECK-NOT: .cfi_adjust_cfa_offset
+define void @foo(i8) {
+entry-block:
+  switch i8 %0, label %bb2 [
+    i8 1, label %bb1
+    i8 2, label %bb2
+    i8 3, label %bb3
+    i8 4, label %bb4
+    i8 5, label %bb5
+  ]
+
+bb1:
+  ret void
+
+bb2:
+  ret void
+
+bb3:
+  ret void
+
+bb4:
+  ret void
+
+bb5:
+  ret void
+}