Enable stripping of multiple DILocation on !llvm.loop metadata

[tejohnson]

Summary

I found that stripDebugInfo was still leaving significant amounts of
debug info due to !llvm.loop that contained DILocation after stripping.
The support for stripping debug info on !llvm.loop added in r293377 only
removes a single DILocation. Enhance that to remove all DILocation from
!llvm.loop.

[hfinkel]

LGTM

lib/IR/DebugInfo.cpp

bool DebugInfoFinder::addScope(DIScope *Scope) {
   if (!NodesSeen.insert(Scope).second)
     return false;
   Scopes.push_back(Scope);
   return true;
 }
 
 static llvm::MDNode *stripDebugLocFromLoopID(llvm::MDNode *N) {
   assert(N->op_begin() != N->op_end() && "Missing self reference?");
-  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())
+  // if there is no debug location, we do not have to rewrite this MDNode.
+  if (std::none_of(N->op_begin() + 1, N->op_end(), [](const MDOperand &Op) {
+        return isa<DILocation>(Op.get());
+      }))
     return N;
 
-  // There is only the debug location without any actual loop metadata, hence we
+  // If there is only the debug location without any actual loop metadata, we
   // can remove the metadata.
-  if (N->getNumOperands() == 2)
+  if (std::none_of(N->op_begin() + 1, N->op_end(), [](const MDOperand &Op) {
+        return !isa<DILocation>(Op.get());
+      }))
     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());
+  // Add all non-debug location operands back.
+  for (auto Op = N->op_begin() + 1; Op != N->op_end(); Op++) {
+    if (!isa<DILocation>(*Op))
+      Args.push_back(*Op);
+  }
 
   // Set the first operand to itself.
   MDNode *LoopID = MDNode::get(N->getContext(), Args);
   LoopID->replaceOperandWith(0, LoopID);
   return LoopID;
 }
 
 bool llvm::stripDebugInfo(Function &F) {

test/DebugInfo/strip-loop-metadata.ll

 while.body:
   call void @_Z3barv(), !dbg !17
   br label %while.body, !dbg !18, !llvm.loop !19
 
 return:
   ret void, !dbg !21
 }
 
+; CHECK-LABEL: _Z5test3v
+; CHECK: br {{.*}} !llvm.loop [[LOOP2:![0-9]+]]
+define void @_Z5test3v() !dbg !22 {
+entry:
+  br label %while.body, !dbg !23
+
+while.body:
+  call void @_Z3barv(), !dbg !24
+  br label %while.body, !dbg !25, !llvm.loop !26
+
+return:
+  ret void, !dbg !28
+}
+
+; CHECK-LABEL: _Z5test4v
+; CHECK-NOT: br {{.*}} !llvm.loop
+define void @_Z5test4v() !dbg !30 {
+entry:
+  br label %while.body, !dbg !31
+
+while.body:
+  call void @_Z3barv(), !dbg !32
+  br label %while.body, !dbg !33, !llvm.loop !34
+
+return:
+  ret void, !dbg !36
+}
+
 !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}

 !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)
+!22 = distinct !DISubprogram(name: "test3", scope: !1, file: !1, line: 8, type: !8, isLocal: false, isDefinition: true, scopeLine: 8, flags: DIFlagPrototyped, isOptimized: false, unit: !0, variables: !2)
+!23 = !DILocation(line: 8, column: 14, scope: !22)
+!24 = !DILocation(line: 11, column: 5, scope: !22)
+!25 = !DILocation(line: 10, column: 3, scope: !22)
+!26 = distinct !{!26, !23, !29, !27}
+!27 = !{!"llvm.loop.unroll.enable"}
+!28 = !DILocation(line: 12, column: 1, scope: !22)
+!29 = !DILocation(line: 12, column: 1, scope: !22)
+!30 = distinct !DISubprogram(name: "test4", scope: !1, file: !1, line: 8, type: !8, isLocal: false, isDefinition: true, scopeLine: 8, flags: DIFlagPrototyped, isOptimized: false, unit: !0, variables: !2)
+!31 = !DILocation(line: 8, column: 14, scope: !30)
+!32 = !DILocation(line: 11, column: 5, scope: !30)
+!33 = !DILocation(line: 10, column: 3, scope: !30)
+!34 = distinct !{!34, !31, !35}
+!35 = !DILocation(line: 12, column: 1, scope: !30)
+!36 = !DILocation(line: 12, column: 1, scope: !30)
 
 ; 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: [[LOOP2]] = distinct !{[[LOOP2]], [[LOOP_UNROLL]]}
 ; CHECK-NOT: !DILocation