[CodeExtractor] Transfer debug info to extracted function

[vsk]

Summary

After extracting, fix up debug info in both the old and new functions by

1. Pointing line locations and debug intrinsics to the new subprogram scope, and

2. Deleting intrinsics which point to values outside of the new function.

Depends on https://reviews.llvm.org/D72795.

Testing: check-llvm, check-clang, a build of LNT in the -Os -g config
with "-mllvm -hot-cold-split=1" set, and end-to-end debugging of a toy
program which undergoes splitting to verify that lldb can find
variables, single step, etc. in extracted code.

rdar://45507940

[aprantl]

llvm/lib/Transforms/Utils/CodeExtractor.cpp

1388

///

1440

Out of curiosity: anything that can be shared with CloneFunction here?

1489

I'm not sure you actually need to call this when you don't create any new types with cycles.

llvm/test/Transforms/HotColdSplit/split-out-dbg-label.ll

4

Can you add a comment what is being tested here?

llvm/test/Transforms/HotColdSplit/transfer-debug-info.ll

4

and here

[vsk]

Address review feedback.

llvm/lib/Transforms/Utils/CodeExtractor.cpp

1440

Unfortunately not. I actually looked into this before writing the patch, but most of what's needed here is specific to moving instructions from one function to another.

1489

Removed, thanks.

[aprantl]

Looks plausible.

llvm/lib/Transforms/Utils/CodeExtractor.cpp

 #include "llvm/Analysis/BranchProbabilityInfo.h"
 #include "llvm/Analysis/LoopInfo.h"
 #include "llvm/IR/Argument.h"
 #include "llvm/IR/Attributes.h"
 #include "llvm/IR/BasicBlock.h"
 #include "llvm/IR/CFG.h"
 #include "llvm/IR/Constant.h"
 #include "llvm/IR/Constants.h"
+#include "llvm/IR/DIBuilder.h"
 #include "llvm/IR/DataLayout.h"
+#include "llvm/IR/DebugInfoMetadata.h"
 #include "llvm/IR/DerivedTypes.h"
 #include "llvm/IR/Dominators.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/GlobalValue.h"
+#include "llvm/IR/InstIterator.h"
 #include "llvm/IR/InstrTypes.h"
 #include "llvm/IR/Instruction.h"
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/IntrinsicInst.h"
 #include "llvm/IR/Intrinsics.h"
 #include "llvm/IR/LLVMContext.h"
 #include "llvm/IR/MDBuilder.h"
 #include "llvm/IR/Module.h"
for (unsigned I = 0, E = BranchDist.Weights.size(); I < E; ++I) {
     BranchProbability BP(Weight.Amount, BranchDist.Total);
     BPI->setEdgeProbability(CodeReplacer, Weight.TargetNode.Index, BP);
   }
   TI->setMetadata(
       LLVMContext::MD_prof,
       MDBuilder(TI->getContext()).createBranchWeights(BranchWeights));
 }
 
+// Erase debug info intrinsics which refer to values in \p F but aren't in \p F.
+static void eraseDebugIntrinsicsWithNonLocalRefs(Function &F) {
+  for (Instruction &I : instructions(F)) {
+    SmallVector<DbgVariableIntrinsic *, 4> DbgUsers;
+    findDbgUsers(DbgUsers, &I);
+    for (DbgVariableIntrinsic *DVI : DbgUsers)
+      if (DVI->getFunction() != &F)
+        DVI->eraseFromParent();
+  }
+}
+
+/// Fix up the debug info in the old and new functions by pointing line
+/// locations and debug intrinsics to the new subprogram scope, and by deleting
+/// intrinsics which point to values outside of the new function.
+static void fixupDebugInfoPostExtraction(Function &OldFunc, Function &NewFunc,
+                                         CallInst &TheCall) {
+  DISubprogram *OldSP = OldFunc.getSubprogram();
+  LLVMContext &Ctx = OldFunc.getContext();
+
+  // See llvm.org/PR44560, OpenMP passes an invalid subprogram to CodeExtractor.
+  bool NeedWorkaroundForOpenMPIRBuilderBug =
+      OldSP && OldSP->getRetainedNodes()->isTemporary();
+
+  if (!OldSP || NeedWorkaroundForOpenMPIRBuilderBug) {
+    // Erase any debug info the new function contains.
+    stripDebugInfo(NewFunc);
+    // Make sure the old function doesn't contain any non-local metadata refs.
+    eraseDebugIntrinsicsWithNonLocalRefs(NewFunc);
+    return;
+  }
+
+  // Create a subprogram for the new function. Leave out a description of the
+  // function arguments, as the parameters don't correspond to anything at the
+  // source level.
+  assert(OldSP->getUnit() && "Missing compile unit for subprogram");
+  DIBuilder DIB(*OldFunc.getParent(), /*AllowUnresolvedNodes=*/false,
+                OldSP->getUnit());
+  auto SPType = DIB.createSubroutineType(DIB.getOrCreateTypeArray(None));
+  DISubprogram::DISPFlags SPFlags = DISubprogram::SPFlagDefinition |
+                                    DISubprogram::SPFlagOptimized |
+                                    DISubprogram::SPFlagLocalToUnit;
+  auto NewSP = DIB.createFunction(
+      OldSP->getUnit(), NewFunc.getName(), NewFunc.getName(), OldSP->getFile(),
+      /*LineNo=*/0, SPType, /*ScopeLine=*/0, DINode::FlagZero, SPFlags);
+  NewFunc.setSubprogram(NewSP);
+
+  // Debug intrinsics in the new function need to be updated in one of two
+  // ways:
+  //  1) They need to be deleted, because they describe a value in the old
+  //     function.
+  //  2) They need to point to fresh metadata, e.g. because they currently
+  //     point to a variable in the wrong scope.
+  SmallDenseMap<DINode *, DINode *> RemappedMetadata;
+  SmallVector<Instruction *, 4> DebugIntrinsicsToDelete;
+  for (Instruction &I : instructions(NewFunc)) {
+    auto *DII = dyn_cast<DbgInfoIntrinsic>(&I);
+    if (!DII)
+      continue;
+
+    // Point the intrinsic to a fresh label within the new function.
+    if (auto *DLI = dyn_cast<DbgLabelInst>(&I)) {
+      DILabel *OldLabel = DLI->getLabel();
+      DINode *&NewLabel = RemappedMetadata[OldLabel];
+      if (!NewLabel)
+        NewLabel = DILabel::get(Ctx, NewSP, OldLabel->getName(),
+                                OldLabel->getFile(), OldLabel->getLine());
+      DLI->setArgOperand(0, MetadataAsValue::get(Ctx, NewLabel));
+      continue;
+    }
+
+    // If the location isn't a constant or an instruction, delete the
+    // intrinsic.
+    auto *DVI = cast<DbgVariableIntrinsic>(DII);
+    Value *Location = DVI->getVariableLocation();
+    if (!Location ||
+        (!isa<Constant>(Location) && !isa<Instruction>(Location))) {
+      DebugIntrinsicsToDelete.push_back(DVI);
+      continue;
+    }
+
+    // If the variable location is an instruction but isn't in the new
+    // function, delete the intrinsic.
+    Instruction *LocationInst = dyn_cast<Instruction>(Location);
+    if (LocationInst && LocationInst->getFunction() != &NewFunc) {
+      DebugIntrinsicsToDelete.push_back(DVI);
+      continue;
+    }
+
+    // Point the intrinsic to a fresh variable within the new function.
+    DILocalVariable *OldVar = DVI->getVariable();
+    DINode *&NewVar = RemappedMetadata[OldVar];
+    if (!NewVar)
+      NewVar = DIB.createAutoVariable(
+          NewSP, OldVar->getName(), OldVar->getFile(), OldVar->getLine(),
+          OldVar->getType(), /*AlwaysPreserve=*/false, DINode::FlagZero,
+          OldVar->getAlignInBits());
+    DVI->setArgOperand(1, MetadataAsValue::get(Ctx, NewVar));
+  }
+  for (auto *DII : DebugIntrinsicsToDelete)
+    DII->eraseFromParent();
+  DIB.finalizeSubprogram(NewSP);
+  DIB.finalize();
+
+  // Fix up the scope information attached to the line locations in the new
+  // function.
+  for (Instruction &I : instructions(NewFunc)) {
+    if (const DebugLoc &DL = I.getDebugLoc())
+      I.setDebugLoc(DebugLoc::get(DL.getLine(), DL.getCol(), NewSP));
+    else if (isa<CallBase>(&I))
+      // Ensure that inlinable calls have some debug location.
+      I.setDebugLoc(DebugLoc::get(0, 0, NewSP));
+
+    // Loop info metadata may contain line locations. Fix them up.
+    auto updateLoopInfoLoc = [&Ctx,
+                              NewSP](const DILocation &Loc) -> DILocation * {
+      return DILocation::get(Ctx, Loc.getLine(), Loc.getColumn(), NewSP,
+                             nullptr);
+    };
+    updateLoopMetadataDebugLocations(I, updateLoopInfoLoc);
+  }
+  if (!TheCall.getDebugLoc())
+    TheCall.setDebugLoc(DebugLoc::get(0, 0, OldSP));
+
+  eraseDebugIntrinsicsWithNonLocalRefs(NewFunc);
+}
+
 Function *
 CodeExtractor::extractCodeRegion(const CodeExtractorAnalysisCache &CEAC) {
   if (!isEligible())
     return nullptr;
 
   // Assumption: this is a single-entry code region, and the header is the first
   // block in the region.
   BasicBlock *header = *Blocks.begin();
for (PHINode &PN : ExitBB->phis()) {
           PN.setIncomingBlock(i, codeReplacer);
           IncomingCodeReplacerVal = PN.getIncomingValue(i);
         } else
           assert(IncomingCodeReplacerVal == PN.getIncomingValue(i) &&
                  "PHI has two incompatbile incoming values from codeRepl");
       }
     }
 
-  // Erase debug info intrinsics. Variable updates within the new function are
-  // invisible to debuggers. This could be improved by defining a DISubprogram
-  // for the new function.
-  for (BasicBlock &BB : *newFunction) {
-    auto BlockIt = BB.begin();
-    // Remove debug info intrinsics from the new function.
-    while (BlockIt != BB.end()) {
-      Instruction *Inst = &*BlockIt;
-      ++BlockIt;
-      if (isa<DbgInfoIntrinsic>(Inst))
-        Inst->eraseFromParent();
-    }
-    // Remove debug info intrinsics which refer to values in the new function
-    // from the old function.
-    SmallVector<DbgVariableIntrinsic *, 4> DbgUsers;
-    for (Instruction &I : BB)
-      findDbgUsers(DbgUsers, &I);
-    for (DbgVariableIntrinsic *DVI : DbgUsers)
-      DVI->eraseFromParent();
-  }
+  fixupDebugInfoPostExtraction(*oldFunction, *newFunction, *TheCall);
 
   // Mark the new function `noreturn` if applicable. Terminators which resume
   // exception propagation are treated as returning instructions. This is to
   // avoid inserting traps after calls to outlined functions which unwind.
   bool doesNotReturn = none_of(*newFunction, [](const BasicBlock &BB) {
     const Instruction *Term = BB.getTerminator();
     return isa<ReturnInst>(Term) || isa<ResumeInst>(Term);
   });

llvm/test/Transforms/HotColdSplit/split-out-dbg-label.ll

+; RUN: opt -hotcoldsplit -hotcoldsplit-threshold=0 -S < %s | FileCheck %s
+
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.14.0"
+
+; CHECK-LABEL: define {{.*}}@foo.cold.1
+; CHECK: llvm.dbg.label(metadata [[LABEL:![0-9]+]]), !dbg [[LINE:![0-9]+]]
+
+; CHECK: [[FILE:![0-9]+]] = !DIFile
+; CHECK: [[SCOPE:![0-9]+]] = distinct !DISubprogram(name: "foo.cold.1"
+; CHECK: [[LINE]] = !DILocation(line: 1, column: 1, scope: [[SCOPE]]
+; CHECK: [[LABEL]] = !DILabel(scope: [[SCOPE]], name: "bye", file: [[FILE]], line: 28
+
+define void @foo(i32 %arg1) !dbg !6 {
+entry:
+  %var = add i32 0, 0, !dbg !11
+  br i1 undef, label %if.then, label %if.end
+
+if.then:                                          ; preds = %entry
+  ret void
+
+if.end:                                           ; preds = %entry
+  call void @llvm.dbg.label(metadata !12), !dbg !11
+  call void @sink()
+  ret void
+}
+
+declare void @llvm.dbg.label(metadata)
+
+declare void @sink() cold
+
+!llvm.dbg.cu = !{!0}
+!llvm.debugify = !{!3, !4}
+!llvm.module.flags = !{!5}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C, file: !1, producer: "debugify", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "<stdin>", directory: "/")
+!2 = !{}
+!3 = !{i32 7}
+!4 = !{i32 1}
+!5 = !{i32 2, !"Debug Info Version", i32 3}
+!6 = distinct !DISubprogram(name: "foo", linkageName: "foo", scope: null, file: !1, line: 1, type: !7, isLocal: false, isDefinition: true, scopeLine: 1, isOptimized: true, unit: !0, retainedNodes: !8)
+!7 = !DISubroutineType(types: !2)
+!8 = !{!9}
+!9 = !DILocalVariable(name: "1", scope: !6, file: !1, line: 1, type: !10)
+!10 = !DIBasicType(name: "ty32", size: 32, encoding: DW_ATE_unsigned)
+!11 = !DILocation(line: 1, column: 1, scope: !6)
+!12 = !DILabel(scope: !6, name: "bye", file: !1, line: 28)

llvm/test/Transforms/HotColdSplit/transfer-debug-info.ll

+; RUN: opt -hotcoldsplit -hotcoldsplit-threshold=0 -S < %s | FileCheck %s
+
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.14.0"
+
+; CHECK-LABEL: define {{.*}}@foo.cold.1
+; CHECK-NOT: llvm.dbg.value
+
+; CHECK:      [[ADD1:%.*]] = add i32 %{{.*}}, 1{{$}}
+; CHECK-NEXT: llvm.dbg.value(metadata i32 [[ADD1]], metadata [[VAR1:![0-9]+]], metadata !DIExpression()), !dbg [[LINE1:![0-9]+]]
+; CHECK-NEXT: call void @sink(i32 [[ADD1]]), !dbg [[LINE1]]
+; CHECK-NEXT: call void @sink(i32 [[ADD1]]), !dbg [[LINE0:![0-9]+]]
+; CHECK-NEXT: llvm.dbg.value(metadata i32 [[ADD1]], metadata [[VAR1]], metadata !DIExpression(DW_OP_constu, 1, DW_OP_plus, DW_OP_stack_value)
+
+; CHECK: [[FILE:![0-9]+]] = !DIFile(filename: "<stdin>"
+; CHECK: [[EMPTY_MD:![0-9]+]] = !{}
+; CHECK: [[EMPTY_TYPE:![0-9]+]] = !DISubroutineType(types: [[EMPTY_MD]])
+; CHECK: [[NEWSCOPE:![0-9]+]] = distinct !DISubprogram(name: "foo.cold.1", linkageName: "foo.cold.1", scope: null, file: [[FILE]], type: [[EMPTY_TYPE]], spFlags: DISPFlagLocalToUnit | DISPFlagDefinition | DISPFlagOptimized
+
+; CHECK: [[LINE1]] = !DILocation(line: 1, column: 1, scope: [[NEWSCOPE]])
+; CHECK: [[LINE0]] = !DILocation(line: 0, scope: [[NEWSCOPE]])
+
+define void @foo(i32 %arg1) !dbg !6 {
+entry:
+  %var = add i32 0, 0, !dbg !11
+  br i1 undef, label %if.then, label %if.end
+
+if.then:                                          ; preds = %entry
+  ret void
+
+if.end:                                           ; preds = %entry
+  call void @llvm.dbg.value(metadata i32 %arg1, metadata !9, metadata !DIExpression()), !dbg !11
+  %add1 = add i32 %arg1, 1
+  call void @llvm.dbg.value(metadata i32 %add1, metadata !9, metadata !DIExpression()), !dbg !11
+  call void @sink(i32 %add1), !dbg !11
+  call void @sink(i32 %add1)
+  call void @llvm.dbg.value(metadata i32 %add1, metadata !9, metadata !DIExpression(DW_OP_constu, 1, DW_OP_plus, DW_OP_stack_value)), !dbg !11
+  ret void
+}
+
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+declare void @sink(i32) cold
+
+!llvm.dbg.cu = !{!0}
+!llvm.debugify = !{!3, !4}
+!llvm.module.flags = !{!5}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C, file: !1, producer: "debugify", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "<stdin>", directory: "/")
+!2 = !{}
+!3 = !{i32 7}
+!4 = !{i32 1}
+!5 = !{i32 2, !"Debug Info Version", i32 3}
+!6 = distinct !DISubprogram(name: "foo", linkageName: "foo", scope: null, file: !1, line: 1, type: !7, isLocal: false, isDefinition: true, scopeLine: 1, isOptimized: true, unit: !0, retainedNodes: !8)
+!7 = !DISubroutineType(types: !2)
+!8 = !{!9}
+!9 = !DILocalVariable(name: "1", scope: !6, file: !1, line: 1, type: !10)
+!10 = !DIBasicType(name: "ty32", size: 32, encoding: DW_ATE_unsigned)
+!11 = !DILocation(line: 1, column: 1, scope: !6)

llvm/test/Transforms/HotColdSplit/update-split-loop-metadata.ll

+; RUN: opt -hotcoldsplit -hotcoldsplit-threshold=0 -S < %s | FileCheck %s
+
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.14.0"
+
+; CHECK-LABEL: define {{.*}}@basic.cold.1
+; CHECK: br i1 {{.*}}, !llvm.loop [[LOOP_MD:![0-9]+]]
+
+; CHECK: [[SCOPE:![0-9]+]] = distinct !DISubprogram(name: "basic.cold.1"
+; CHECK: [[LOOP_MD]] = distinct !{[[LOOP_MD]], [[LINE:![0-9]+]], [[LINE]]}
+; CHECK: [[LINE]] = !DILocation(line: 1, column: 1, scope: [[SCOPE]])
+
+define void @basic(i32* %p, i32 %k) !dbg !6 {
+entry:
+  %cmp3 = icmp slt i32 0, %k
+  br i1 %cmp3, label %for.body.lr.ph, label %for.end
+
+for.body.lr.ph:                                   ; preds = %entry
+  br label %for.body
+
+for.body:                                         ; preds = %for.body.lr.ph, %for.body
+  %i.05 = phi i32 [ 0, %for.body.lr.ph ], [ %inc, %for.body ]
+  %p.addr.04 = phi i32* [ %p, %for.body.lr.ph ], [ %incdec.ptr, %for.body ]
+  %incdec.ptr = getelementptr inbounds i32, i32* %p.addr.04, i32 1
+  store i32 %i.05, i32* %p.addr.04, align 4
+  %inc = add nsw i32 %i.05, 1
+  call void @sink()
+  %cmp = icmp slt i32 %inc, %k
+  br i1 %cmp, label %for.body, label %for.cond.for.end_crit_edge, !llvm.loop !10
+
+for.cond.for.end_crit_edge:                       ; preds = %for.body
+  br label %for.end
+
+for.end:                                          ; preds = %for.cond.for.end_crit_edge, %entry
+  ret void
+}
+
+declare void @sink() cold
+
+!llvm.dbg.cu = !{!0}
+!llvm.debugify = !{!3, !4}
+!llvm.module.flags = !{!5}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C, file: !1, producer: "debugify", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "<stdin>", directory: "/")
+!2 = !{}
+!3 = !{i32 22}
+!4 = !{i32 12}
+!5 = !{i32 2, !"Debug Info Version", i32 3}
+!6 = distinct !DISubprogram(name: "basic", linkageName: "basic", scope: null, file: !1, line: 1, type: !7, scopeLine: 1, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !8)
+!7 = !DISubroutineType(types: !2)
+!8 = !{}
+!9 = !DILocation(line: 1, column: 1, scope: !6)
+!10 = distinct !{!10, !9, !9}