[DebugInfo] Handle followup loop metadata in updateLoopMetadataDebugLocations (#157557)

Inliner/IROutliner/CodeExtractor all uses the
updateLoopMetadataDebugLocations helper in order to modify debug
location related to loop metadata. However, the helper has only
been updating DILocation nodes found as operands to the first level
of the MD_loop metadata. There could however be more DILocations
as part of the various kinds of followup metadata. A typical example
would be llvm.loop metadata like this

  !6 = distinct !{!6, !7, !8, !9, !10, !11}
  !7 = !DILocation(line: 6, column: 3, scope: !3)
  !8 = !DILocation(line: 7, column: 22, scope: !3)
  !11 = !{!"llvm.loop.distribute.followup_all", !7, !8, ..., !14}
  !14 = !{!"llvm.loop.vectorize.followup_all", !7, !8, ...}

Instead of just updating !7 and !8 in !6, this patch make sure that
we now recursively update the DILocations in !11 and !14 as well.

Fixes #141568

Author: bjope

llvm/lib/IR/DebugInfo.cpp

@@ -375,6 +375,38 @@ bool DebugInfoFinder::addScope(DIScope *Scope) {
   return true;
 }
 
+/// Recursively handle DILocations in followup metadata etc.
+///
+/// TODO: If for example a followup loop metadata would refence itself this
+/// function would go into infinite recursion. We do not expect such cycles in
+/// the loop metadata (except for the self-referencing first element
+/// "LoopID"). However, we could at least handle such situations more gracefully
+/// somehow (e.g. by keeping track of visited nodes and dropping metadata).
+static Metadata *updateLoopMetadataDebugLocationsRecursive(
+    Metadata *MetadataIn, function_ref<Metadata *(Metadata *)> Updater) {
+  const MDTuple *M = dyn_cast_or_null<MDTuple>(MetadataIn);
+  // The loop metadata options should start with a MDString.
+  if (!M || M->getNumOperands() < 1 || !isa<MDString>(M->getOperand(0)))
+    return MetadataIn;
+
+  bool Updated = false;
+  SmallVector<Metadata *, 4> MDs{M->getOperand(0)};
+  for (Metadata *MD : llvm::drop_begin(M->operands())) {
+    if (!MD) {
+      MDs.push_back(nullptr);
+      continue;
+    }
+    Metadata *NewMD =
+        Updater(updateLoopMetadataDebugLocationsRecursive(MD, Updater));
+    if (NewMD)
+      MDs.push_back(NewMD);
+    Updated |= NewMD != MD;
+  }
+
+  assert(!M->isDistinct() && "M should not be distinct.");
+  return Updated ? MDNode::get(M->getContext(), MDs) : MetadataIn;
+}
+
 static MDNode *updateLoopMetadataDebugLocationsImpl(
     MDNode *OrigLoopID, function_ref<Metadata *(Metadata *)> Updater) {
   assert(OrigLoopID && OrigLoopID->getNumOperands() > 0 &&
@@ -385,11 +417,11 @@ static MDNode *updateLoopMetadataDebugLocationsImpl(
   // Save space for the self-referential LoopID.
   SmallVector<Metadata *, 4> MDs = {nullptr};
 
-  for (unsigned i = 1; i < OrigLoopID->getNumOperands(); ++i) {
-    Metadata *MD = OrigLoopID->getOperand(i);
+  for (Metadata *MD : llvm::drop_begin(OrigLoopID->operands())) {
     if (!MD)
       MDs.push_back(nullptr);
-    else if (Metadata *NewMD = Updater(MD))
+    else if (Metadata *NewMD = Updater(
+                 updateLoopMetadataDebugLocationsRecursive(MD, Updater)))
       MDs.push_back(NewMD);
   }
 

llvm/test/Transforms/Inline/dilocation-loop-metadata-update.ll

@@ -0,0 +1,83 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt < %s -passes=inline -S | FileCheck %s
+
+; When inlining we need to update DILocation recursively for the followup
+; metadata when updating llvm.loop metadata.
+
+define void @a() !dbg !3 {
+; CHECK-LABEL: define void @a(
+; CHECK-SAME: ) !dbg [[DBG3:![0-9]+]] {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    br label %[[FOR_BODY:.*]]
+; CHECK:       [[FOR_BODY]]:
+; CHECK-NEXT:    br label %[[FOR_BODY]], !llvm.loop [[LOOP6:![0-9]+]]
+;
+entry:
+  br label %for.body
+
+for.body:                                         ; preds = %for.body, %entry
+  br label %for.body, !llvm.loop !6
+}
+
+define void @f() !dbg !17 {
+; CHECK-LABEL: define void @f(
+; CHECK-SAME: ) !dbg [[DBG17:![0-9]+]] {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    br label %[[A_EXIT:.*]]
+; CHECK:       [[A_EXIT]]:
+; CHECK-NEXT:    br label %[[A_EXIT]], !llvm.loop [[LOOP18:![0-9]+]]
+; CHECK:       [[A_EXIT1:.*:]]
+; CHECK-NEXT:    ret void
+;
+entry:
+  call void @a(), !dbg !18
+  ret void
+}
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C11, file: !1, producer: "clang", isOptimized: true, runtimeVersion: 0, emissionKind: NoDebug, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "foo.c", directory: "/")
+!2 = !{i32 2, !"Debug Info Version", i32 3}
+!3 = distinct !DISubprogram(name: "a", scope: !1, file: !1, line: 3, type: !4, scopeLine: 3, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0)
+!4 = !DISubroutineType(types: !5)
+!5 = !{}
+!6 = distinct !{!6, !7, !8, !9, !10, !11}
+!7 = !DILocation(line: 6, column: 3, scope: !3)
+!8 = !DILocation(line: 7, column: 22, scope: !3)
+!9 = !{!"llvm.loop.mustprogress"}
+!10 = !{!"llvm.loop.distribute.enable", i1 true}
+!11 = !{!"llvm.loop.distribute.followup_all", !7, !8, !9, !12, !13, !14}
+!12 = !{!"llvm.loop.vectorize.width", i32 8}
+!13 = !{!"llvm.loop.vectorize.enable", i1 true}
+!14 = !{!"llvm.loop.vectorize.followup_all", !7, !8, !9, !15, !16}
+!15 = !{!"llvm.loop.isvectorized"}
+!16 = !{!"llvm.loop.unroll.count", i32 1}
+!17 = distinct !DISubprogram(name: "f", scope: !1, file: !1, line: 9, type: !4, scopeLine: 9, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0)
+!18 = !DILocation(line: 9, column: 12, scope: !17)
+;.
+; CHECK: [[META0:![0-9]+]] = distinct !DICompileUnit(language: DW_LANG_C11, file: [[META1:![0-9]+]], producer: "clang", isOptimized: true, runtimeVersion: 0, emissionKind: NoDebug, splitDebugInlining: false, nameTableKind: None)
+; CHECK: [[META1]] = !DIFile(filename: "{{.*}}foo.c", directory: {{.*}})
+; CHECK: [[DBG3]] = distinct !DISubprogram(name: "a", scope: [[META1]], file: [[META1]], line: 3, type: [[META4:![0-9]+]], scopeLine: 3, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: [[META0]])
+; CHECK: [[META4]] = !DISubroutineType(types: [[META5:![0-9]+]])
+; CHECK: [[META5]] = !{}
+; CHECK: [[LOOP6]] = distinct !{[[LOOP6]], [[META7:![0-9]+]], [[META8:![0-9]+]], [[META9:![0-9]+]], [[META10:![0-9]+]], [[META11:![0-9]+]]}
+; CHECK: [[META7]] = !DILocation(line: 6, column: 3, scope: [[DBG3]])
+; CHECK: [[META8]] = !DILocation(line: 7, column: 22, scope: [[DBG3]])
+; CHECK: [[META9]] = !{!"llvm.loop.mustprogress"}
+; CHECK: [[META10]] = !{!"llvm.loop.distribute.enable", i1 true}
+; CHECK: [[META11]] = !{!"llvm.loop.distribute.followup_all", [[META7]], [[META8]], [[META9]], [[META12:![0-9]+]], [[META13:![0-9]+]], [[META14:![0-9]+]]}
+; CHECK: [[META12]] = !{!"llvm.loop.vectorize.width", i32 8}
+; CHECK: [[META13]] = !{!"llvm.loop.vectorize.enable", i1 true}
+; CHECK: [[META14]] = !{!"llvm.loop.vectorize.followup_all", [[META7]], [[META8]], [[META9]], [[META15:![0-9]+]], [[META16:![0-9]+]]}
+; CHECK: [[META15]] = !{!"llvm.loop.isvectorized"}
+; CHECK: [[META16]] = !{!"llvm.loop.unroll.count", i32 1}
+; CHECK: [[DBG17]] = distinct !DISubprogram(name: "f", scope: [[META1]], file: [[META1]], line: 9, type: [[META4]], scopeLine: 9, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: [[META0]])
+; CHECK: [[LOOP18]] = distinct !{[[LOOP18]], [[META19:![0-9]+]], [[META21:![0-9]+]], [[META9]], [[META10]], [[META22:![0-9]+]]}
+; CHECK: [[META19]] = !DILocation(line: 6, column: 3, scope: [[DBG3]], inlinedAt: [[META20:![0-9]+]])
+; CHECK: [[META20]] = distinct !DILocation(line: 9, column: 12, scope: [[DBG17]])
+; CHECK: [[META21]] = !DILocation(line: 7, column: 22, scope: [[DBG3]], inlinedAt: [[META20]])
+; CHECK: [[META22]] = !{!"llvm.loop.distribute.followup_all", [[META19]], [[META21]], [[META9]], [[META12]], [[META13]], [[META23:![0-9]+]]}
+; CHECK: [[META23]] = !{!"llvm.loop.vectorize.followup_all", [[META19]], [[META21]], [[META9]], [[META15]], [[META16]]}
+;.