[framelowering] Improve tracking of first CS pop instruction.

Summary: This patch makes sure FirstCSPop and MBBI never point to DBG_VALUE instructions, which affected the code generated.

Reviewers: mkuper, aprantl, MatzeB

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D27343

llvm-svn: 288794

llvm/lib/Target/X86/X86FrameLowering.cpp

@@ -1550,19 +1550,22 @@ void X86FrameLowering::emitEpilogue(MachineFunction &MF,
   }
   uint64_t SEHStackAllocAmt = NumBytes;
 
+  MachineBasicBlock::iterator FirstCSPop = MBBI;
   // Skip the callee-saved pop instructions.
   while (MBBI != MBB.begin()) {
     MachineBasicBlock::iterator PI = std::prev(MBBI);
     unsigned Opc = PI->getOpcode();
 
-    if ((Opc != X86::POP32r || !PI->getFlag(MachineInstr::FrameDestroy)) &&
-        (Opc != X86::POP64r || !PI->getFlag(MachineInstr::FrameDestroy)) &&
-        Opc != X86::DBG_VALUE && !PI->isTerminator())
-      break;
+    if (Opc != X86::DBG_VALUE && !PI->isTerminator()) {
+      if ((Opc != X86::POP32r || !PI->getFlag(MachineInstr::FrameDestroy)) &&
+          (Opc != X86::POP64r || !PI->getFlag(MachineInstr::FrameDestroy)))
+        break;
+      FirstCSPop = PI;
+    }
 
     --MBBI;
   }
-  MachineBasicBlock::iterator FirstCSPop = MBBI;
+  MBBI = FirstCSPop;
 
   if (TargetMBB) {
     // Fill EAX/RAX with the address of the target block.

llvm/test/CodeGen/X86/frame-lowering-debug-intrinsic.ll

@@ -0,0 +1,41 @@
+; Test ensuring debug intrinsics do not affect generated function prologue.
+;
+; RUN: llc -O1 -mtriple=x86_64-unknown-unknown -o - %s | FileCheck %s
+
+
+define i64 @noDebug(i64 %a) {
+  %call = call i64 @fn(i64 %a, i64 0)
+  ret i64 %call
+}
+
+; CHECK-LABEL: noDebug
+; CHECK: popq %rcx
+; CHECK: ret
+
+
+define i64 @withDebug(i64 %a) !dbg !4 {
+  %call = call i64 @fn(i64 %a, i64 0)
+  tail call void @llvm.dbg.value(metadata i64 %call, i64 0, metadata !5, metadata !6), !dbg !7
+  ret i64 %call
+}
+
+; CHECK-LABEL: withDebug
+; CHECK: popq %rcx
+; CHECK: ret
+
+
+declare i64 @fn(i64, i64)
+
+declare void @llvm.dbg.value(metadata, i64, metadata, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2,!3}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 4.0.0")
+!1 = !DIFile(filename: "test.c", directory: "/")
+!2 = !{i32 2, !"Dwarf Version", i32 4}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!4 = distinct !DISubprogram(name: "withDebug", unit: !0)
+!5 = !DILocalVariable(name: "w", scope: !4)
+!6 = !DIExpression()
+!7 = !DILocation(line: 210, column: 12, scope: !4)