[DWARF] Incorrect prologue end line record.

A prologue-end line record is emitted with an incorrect associated address,
which causes a debugger to show the beginning of function body to be inside
the prologue.

Patch written by Carlos Alberto Enciso.

Differential Revision: https://reviews.llvm.org/D37625

llvm-svn: 313047

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp

@@ -1158,7 +1158,9 @@ void DwarfDebug::beginInstruction(const MachineInstr *MI) {
     return;
 
   // Check if source location changes, but ignore DBG_VALUE and CFI locations.
-  if (MI->isMetaInstruction())
+  // If the instruction is part of the function frame setup code, do not emit
+  // any line record, as there is no correspondence with any user code.
+  if (MI->isMetaInstruction() || MI->getFlag(MachineInstr::FrameSetup))
     return;
   const DebugLoc &DL = MI->getDebugLoc();
   // When we emit a line-0 record, we don't update PrevInstLoc; so look at

llvm/test/DebugInfo/X86/invalid-prologue-end.ll

@@ -0,0 +1,91 @@
+; RUN: llc -mtriple=x86_64-linux-gnu -filetype=asm %s -o - | FileCheck %s
+
+; The prologue-end line record must be emitted after the last instruction that
+; is part of the function frame setup code and before the instruction that marks
+; the beginning of the function body.
+;
+; For the given test, generated from:
+;
+; 1 extern int get_arg();
+; 2 extern void func(int x);
+; 3
+; 4 int main()
+; 5 {
+; 6   int a;
+; 7   func(get_arg());
+; 8 }
+; 9
+
+; The prologue-end line record is emitted with an incorrect associated address,
+; which causes a debugger to show the beginning of function body to be inside
+; the prologue.
+
+; This can be seen in the following trimmed assembler output:
+;
+; main:
+;   ...
+; 	.loc	1 7 0 prologue_end
+; 	pushq	%rax
+; .Lcfi0:
+; 	.cfi_def_cfa_offset 16
+; 	callq	_Z7get_argv
+;   ...
+; 	retq
+
+; The instruction 'pushq %rax' is part of the frame setup code.
+
+; The correct location for the prologue-end line information is just before
+; the call to '_Z7get_argv', as illustrated in the following trimmed
+; assembler output:
+;
+; main:
+;   ...
+; 	pushq	%rax
+; .Lcfi0:
+; 	.cfi_def_cfa_offset 16
+; 	.loc	1 7 0 prologue_end
+; 	callq	_Z7get_argv
+;   ...
+; 	retq
+
+; Check that the generated assembler matches the following sequence:
+
+; CHECK:        pushq	%rax
+; CHECK-NEXT: .Lcfi0:
+; CHECK-NEXT:   .cfi_def_cfa_offset 16
+; CHECK-NEXT:   .loc	1 7 0 prologue_end {{.*}}# invalid-prologue-end.cpp:7:0
+; CHECK-NEXT:   callq	_Z7get_argv
+
+define i32 @main() #0 !dbg !8 {
+  %1 = alloca i32, align 4
+  call void @llvm.dbg.declare(metadata i32* %1, metadata !12, metadata !DIExpression()), !dbg !13
+  %2 = call i32 @_Z7get_argv(), !dbg !14
+  call void @_Z4funci(i32 %2), !dbg !14
+  ret i32 0, !dbg !15
+}
+
+declare void @llvm.dbg.declare(metadata, metadata, metadata) #1
+
+declare void @_Z4funci(i32) #2
+declare i32 @_Z7get_argv() #2
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5, !6}
+!llvm.ident = !{!7}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 6.0.0 (trunk 312775)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "invalid-prologue-end.cpp", directory: "D:\5C93830")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 2}
+!6 = !{i32 7, !"PIC Level", i32 2}
+!7 = !{!"clang version 6.0.0 (trunk 312775)"}
+!8 = distinct !DISubprogram(name: "main", scope: !1, file: !1, line: 4, type: !9, isLocal: false, isDefinition: true, scopeLine: 5, flags: DIFlagPrototyped, isOptimized: false, unit: !0, variables: !2)
+!9 = !DISubroutineType(types: !10)
+!10 = !{!11}
+!11 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!12 = !DILocalVariable(name: "a", scope: !8, file: !1, line: 6, type: !11)
+!13 = !DILocation(line: 6, scope: !8)
+!14 = !DILocation(line: 7, scope: !8)
+!15 = !DILocation(line: 8, scope: !8)