stripDebugInfo() should remove DILocation's found in !llvm.loop metadata

[dsanders]

Summary

Patch by Michele Scandale
(with a small tweak to 'CHECK-NOT' the last DILocation in the test)

[dsanders]

lib/IR/DebugInfo.cpp

244

Can N->op_begin() == N->op_end() ever? If so, I think this is incorrect.
If not, maybe we should assert it?

I believe the first operand is always a self-reference (e.g. !13 in the test). I'll add an assert

[dsanders]

Add assertion

[dsanders]

ping

[dsanders]

ping

lib/IR/DebugInfo.cpp

bool DebugInfoFinder::addScope(DIScope *Scope) {
   if (Scope->getNumOperands() == 0)
     return false;
   if (!NodesSeen.insert(Scope).second)
     return false;
   Scopes.push_back(Scope);
   return true;
 }
 
+static llvm::MDNode *stripDebugLocFromLoopID(llvm::MDNode *N) {
+  auto DebugLocOp =
+      std::find_if(N->op_begin() + 1, N->op_end(), [](const MDOperand &Op) {
+        return isa<DILocation>(Op.get());
+      });
+
+  // No debug location, we do not have to rewrite this MDNode.
+  if (DebugLocOp == N->op_end())
+    return N;
+
+  // There is only the debug location without any actual loop metadata, hence we
+  // can remove the metadata.
+  if (N->getNumOperands() == 2)
+    return nullptr;
+
+  SmallVector<Metadata *, 4> Args;
+  // Reserve operand 0 for loop id self reference.
+  auto TempNode = MDNode::getTemporary(N->getContext(), None);
+  Args.push_back(TempNode.get());
+  Args.append(N->op_begin() + 1, DebugLocOp);
+  Args.append(DebugLocOp + 1, N->op_end());
+
+  // Set the first operand to itself.
+  MDNode *LoopID = MDNode::get(N->getContext(), Args);
+  LoopID->replaceOperandWith(0, LoopID);
+  return LoopID;
+}
+
 bool llvm::stripDebugInfo(Function &F) {
   bool Changed = false;
   if (F.getSubprogram()) {
     Changed = true;
     F.setSubprogram(nullptr);
   }
 
+  llvm::DenseMap<llvm::MDNode*, llvm::MDNode*> LoopIDsMap;
   for (BasicBlock &BB : F) {
     for (auto II = BB.begin(), End = BB.end(); II != End;) {
       Instruction &I = *II++; // We may delete the instruction, increment now.
       if (isa<DbgInfoIntrinsic>(&I)) {
         I.eraseFromParent();
         Changed = true;
         continue;
       }
       if (I.getDebugLoc()) {
         Changed = true;
         I.setDebugLoc(DebugLoc());
       }
     }
+
+    auto *TermInst = BB.getTerminator();
+    if (auto *LoopID = TermInst->getMetadata(LLVMContext::MD_loop)) {
+      auto *NewLoopID = LoopIDsMap.lookup(LoopID);
+      if (!NewLoopID)
+        NewLoopID = LoopIDsMap[LoopID] = stripDebugLocFromLoopID(LoopID);
+      if (NewLoopID != LoopID)
+        TermInst->setMetadata(LLVMContext::MD_loop, NewLoopID);
+    }
   }
   return Changed;
 }
 
 bool llvm::StripDebugInfo(Module &M) {
   bool Changed = false;
 
   for (Module::named_metadata_iterator NMI = M.named_metadata_begin(),

test/DebugInfo/strip-loop-metadata.ll

+; RUN: opt -S -strip-debug < %s | FileCheck %s
+
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.12.0"
+
+; CHECK-LABEL: _Z5test1v
+; CHECK-NOT: br {{.*}} !llvm.loop
+define void @_Z5test1v() !dbg !7 {
+entry:
+  br label %while.body, !dbg !9
+
+while.body:
+  call void @_Z3barv(), !dbg !10
+  br label %while.body, !dbg !11, !llvm.loop !13
+
+return:
+  ret void, !dbg !14
+}
+
+declare void @_Z3barv()
+
+; CHECK-LABEL: _Z5test2v
+; CHECK: br {{.*}} !llvm.loop [[LOOP:![0-9]+]]
+define void @_Z5test2v() !dbg !15 {
+entry:
+  br label %while.body, !dbg !16
+
+while.body:
+  call void @_Z3barv(), !dbg !17
+  br label %while.body, !dbg !18, !llvm.loop !19
+
+return:
+  ret void, !dbg !21
+}
+
+!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 4.0.0", isOptimized: false, runtimeVersion: 0, emissionKind: LineTablesOnly, enums: !2)
+!1 = !DIFile(filename: "test.cpp", directory: "/tmp")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"PIC Level", i32 2}
+!6 = !{!"clang version 4.0.0"}
+!7 = distinct !DISubprogram(name: "test1", scope: !1, file: !1, line: 3, type: !8, isLocal: false, isDefinition: true, scopeLine: 3, flags: DIFlagPrototyped, isOptimized: false, unit: !0, variables: !2)
+!8 = !DISubroutineType(types: !2)
+!9 = !DILocation(line: 4, column: 3, scope: !7)
+!10 = !DILocation(line: 5, column: 5, scope: !7)
+!11 = !DILocation(line: 4, column: 3, scope: !12)
+!12 = !DILexicalBlockFile(scope: !7, file: !1, discriminator: 1)
+!13 = distinct !{!13, !9}
+!14 = !DILocation(line: 6, column: 1, scope: !7)
+!15 = distinct !DISubprogram(name: "test2", scope: !1, file: !1, line: 8, type: !8, isLocal: false, isDefinition: true, scopeLine: 8, flags: DIFlagPrototyped, isOptimized: false, unit: !0, variables: !2)
+!16 = !DILocation(line: 8, column: 14, scope: !15)
+!17 = !DILocation(line: 11, column: 5, scope: !15)
+!18 = !DILocation(line: 10, column: 3, scope: !15)
+!19 = distinct !{!19, !16, !20}
+!20 = !{!"llvm.loop.unroll.enable"}
+!21 = !DILocation(line: 12, column: 1, scope: !15)
+
+; CHECK-NOT: !DICompileUnit
+; CHECK-NOT: !DIFile
+; CHECK-NOT: !DISubprogram
+; CHECK-NOT: !DISubroutineType
+; CHECK-NOT: !DILocation
+; CHECK-NOT: !DILexicalBlockFile
+; CHECK: [[LOOP]] = distinct !{[[LOOP]], [[LOOP_UNROLL:![0-9]+]]}
+; CHECK-NEXT: [[LOOP_UNROLL]] = !{!"llvm.loop.unroll.enable"}
+; CHECK-NOT: !DILocation