Fix out-of-order stepping behavior in programs with sunk instructions.

MachineSink attempts to place instructions near the basic blocks where
they are needed.  Once an instruction has been sunk, its location
relative to other instructions no longer is consistent with the
original source code. In order to ensure correct stepping in the
debugger, the debug location for sunk instructions is either merged
with the insertion point or erased if the target successor block is
empty.

Originally submitted as r318679, revised to fix sanitizer failure and
improve testing.

Patch by Matthew Voss!

Differential Revision: https://reviews.llvm.org/D39933

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@320216 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/MachineSink.cpp

@@ -38,6 +38,7 @@
 #include "llvm/CodeGen/TargetSubtargetInfo.h"
 #include "llvm/IR/BasicBlock.h"
 #include "llvm/IR/LLVMContext.h"
+#include "llvm/IR/DebugInfoMetadata.h"
 #include "llvm/Pass.h"
 #include "llvm/Support/BranchProbability.h"
 #include "llvm/Support/CommandLine.h"
@@ -868,11 +869,20 @@ bool MachineSinking::SinkInstruction(MachineInstr &MI, bool &SawStore,
   SmallVector<MachineInstr *, 2> DbgValuesToSink;
   collectDebugValues(MI, DbgValuesToSink);
 
+  // Merge or erase debug location to ensure consistent stepping in profilers
+  // and debuggers.
+  if (!SuccToSinkTo->empty() && InsertPos != SuccToSinkTo->end())
+    MI.setDebugLoc(DILocation::getMergedLocation(MI.getDebugLoc(),
+                                                 InsertPos->getDebugLoc()));
+  else
+    MI.setDebugLoc(DebugLoc());
+
+
   // Move the instruction.
   SuccToSinkTo->splice(InsertPos, ParentBlock, MI,
                        ++MachineBasicBlock::iterator(MI));
 
-  // Move debug values.
+  // Move previously adjacent debug value instructions to the insert position.
   for (SmallVectorImpl<MachineInstr *>::iterator DBI = DbgValuesToSink.begin(),
          DBE = DbgValuesToSink.end(); DBI != DBE; ++DBI) {
     MachineInstr *DbgMI = *DBI;

test/CodeGen/X86/machinesink-merge-debuginfo.ll

@@ -0,0 +1,56 @@
+; RUN: llc -simplify-mir -stop-after=machine-sink < %s -o - | FileCheck %s
+
+; ModuleID = 'test-sink-debug.cpp'
+source_filename = "test-sink-debug.cpp"
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; Function Attrs: nounwind readnone uwtable
+define double @_Z3fooddb(double %x, double %y, i1 zeroext %c) local_unnamed_addr !dbg !7 {
+  tail call void @llvm.dbg.value(metadata double %x, metadata !13, metadata !DIExpression()), !dbg !16
+  tail call void @llvm.dbg.value(metadata double %y, metadata !14, metadata !DIExpression()), !dbg !16
+  tail call void @llvm.dbg.value(metadata i1 %c, metadata !15, metadata !DIExpression()), !dbg !16
+  %a = fdiv double %x, 3.000000e+00
+  %b = fdiv double %y, 5.000000e+00, !dbg !17
+  br i1 %c, label %first, label %second
+first:
+  %e = fadd double %a, 1.000000e+00
+  br label %final
+second:
+  %f = fadd double %b, 1.000000e+00, !dbg !17
+; CHECK:  debug-location !17
+; CHECK:  debug-location !17
+  br label %final
+final:
+  %cond = phi double [%e, %first], [%f, %second]
+  %d = fadd double %cond, 1.000000e+00
+  ret double %d
+}
+
+; Function Attrs: nounwind readnone speculatable
+declare void @llvm.dbg.value(metadata, metadata, metadata) #1
+
+attributes #1 = { nounwind readnone speculatable }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 6.0.0 (trunk 313291)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "test-sink-debug.cpp", directory: "/tmp")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{!"clang version 6.0.0 (trunk 313291)"}
+!7 = distinct !DISubprogram(name: "foo", linkageName: "_Z3fooddb", scope: !1, file: !1, line: 1, type: !8, isLocal: false, isDefinition: true, scopeLine: 1, flags: DIFlagPrototyped, isOptimized: true, unit: !0, variables: !12)
+!8 = !DISubroutineType(types: !9)
+!9 = !{!10, !10, !10, !11}
+!10 = !DIBasicType(name: "double", size: 64, encoding: DW_ATE_float)
+!11 = !DIBasicType(name: "bool", size: 8, encoding: DW_ATE_boolean)
+!12 = !{!13, !14, !15}
+!13 = !DILocalVariable(name: "x", arg: 1, scope: !7, file: !1, line: 1, type: !10)
+!14 = !DILocalVariable(name: "y", arg: 2, scope: !7, file: !1, line: 1, type: !10)
+!15 = !DILocalVariable(name: "c", arg: 3, scope: !7, file: !1, line: 1, type: !11)
+!16 = !DILocation(line: 1, column: 19, scope: !7)
+!17 = !DILocation(line: 2, column: 26, scope: !7)

test/CodeGen/X86/machinesink-null-debuginfo.ll

@@ -0,0 +1,49 @@
+; RUN: llc -simplify-mir -stop-after=machine-sink < %s -o - | FileCheck %s
+
+; ModuleID = 'test-sink-debug.cpp'
+source_filename = "test-sink-debug.cpp"
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; Function Attrs: nounwind readnone uwtable
+define double @_Z3fooddb(double %x, double %y, i1 zeroext %c) local_unnamed_addr !dbg !7 {
+  tail call void @llvm.dbg.value(metadata double %x, metadata !13, metadata !DIExpression()), !dbg !16
+  tail call void @llvm.dbg.value(metadata double %y, metadata !14, metadata !DIExpression()), !dbg !17
+  tail call void @llvm.dbg.value(metadata i1 %c, metadata !15, metadata !DIExpression()), !dbg !18
+  %a = fdiv double %x, 3.000000e+00
+  %b = fdiv double %y, 5.000000e+00, !dbg !21
+  %cond = select i1 %c,  double %a, double %b
+; CHECK-NOT: debug-location !21
+  ret double %cond, !dbg !22
+}
+
+; Function Attrs: nounwind readnone speculatable
+declare void @llvm.dbg.value(metadata, metadata, metadata) #1
+
+attributes #1 = { nounwind readnone speculatable }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 6.0.0 (trunk 313291)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "test-sink-debug.cpp", directory: "/tmp")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{!"clang version 6.0.0 (trunk 313291)"}
+!7 = distinct !DISubprogram(name: "foo", linkageName: "_Z3fooddb", scope: !1, file: !1, line: 1, type: !8, isLocal: false, isDefinition: true, scopeLine: 1, flags: DIFlagPrototyped, isOptimized: true, unit: !0, variables: !12)
+!8 = !DISubroutineType(types: !9)
+!9 = !{!10, !10, !10, !11}
+!10 = !DIBasicType(name: "double", size: 64, encoding: DW_ATE_float)
+!11 = !DIBasicType(name: "bool", size: 8, encoding: DW_ATE_boolean)
+!12 = !{!13, !14, !15}
+!13 = !DILocalVariable(name: "x", arg: 1, scope: !7, file: !1, line: 1, type: !10)
+!14 = !DILocalVariable(name: "y", arg: 2, scope: !7, file: !1, line: 1, type: !10)
+!15 = !DILocalVariable(name: "c", arg: 3, scope: !7, file: !1, line: 1, type: !11)
+!16 = !DILocation(line: 1, column: 19, scope: !7)
+!17 = !DILocation(line: 1, column: 29, scope: !7)
+!18 = !DILocation(line: 1, column: 37, scope: !7)
+!21 = !DILocation(line: 2, column: 26, scope: !7)
+!22 = !DILocation(line: 2, column: 3, scope: !7)