[Coro] Prebuild a module-level debug info set and share it between all coroutine clones (llvm#118628)

Summary:
CoroCloner, by calling into CloneFunctionInto, does a lot of repeated
work priming DIFinder and building a list of common module-level debug
info metadata. For programs compiled with full debug info this can get
very expensive.

This diff builds the data once and shares it between all clones.

Anecdata for a sample cpp source file compiled with full debug info:

|                 | Baseline | IdentityMD set | Prebuilt CommonDI (cur.) |
|-----------------|----------|----------------|--------------------------|
| CoroSplitPass   | 306ms    | 221ms          | 68ms                     |
| CoroCloner      | 101ms    | 72ms           | 0.5ms                    |
| CollectCommonDI | -        | -              | 63ms                     |
| Speed up        | 1x       | 1.4x           | 4.5x                     |

Note that CollectCommonDebugInfo happens once *per coroutine* rather than per clone.

Test Plan:
ninja check-llvm-unit
ninja check-llvm

Compiled a sample internal source file, checked time trace output for scope timings.

Author: artempyanykh

llvm/lib/Transforms/Coroutines/CoroCloner.h

@@ -48,6 +48,9 @@ class BaseCloner {
   CloneKind FKind;
   IRBuilder<> Builder;
   TargetTransformInfo &TTI;
+  // Common module-level metadata that's shared between all coroutine clones and
+  // doesn't need to be cloned itself.
+  const MetadataSetTy &CommonDebugInfo;
 
   ValueToValueMapTy VMap;
   Function *NewF = nullptr;
@@ -60,12 +63,12 @@ class BaseCloner {
   /// Create a cloner for a continuation lowering.
   BaseCloner(Function &OrigF, const Twine &Suffix, coro::Shape &Shape,
              Function *NewF, AnyCoroSuspendInst *ActiveSuspend,
-             TargetTransformInfo &TTI)
+             TargetTransformInfo &TTI, const MetadataSetTy &CommonDebugInfo)
       : OrigF(OrigF), Suffix(Suffix), Shape(Shape),
         FKind(Shape.ABI == ABI::Async ? CloneKind::Async
                                       : CloneKind::Continuation),
-        Builder(OrigF.getContext()), TTI(TTI), NewF(NewF),
-        ActiveSuspend(ActiveSuspend) {
+        Builder(OrigF.getContext()), TTI(TTI), CommonDebugInfo(CommonDebugInfo),
+        NewF(NewF), ActiveSuspend(ActiveSuspend) {
     assert(Shape.ABI == ABI::Retcon || Shape.ABI == ABI::RetconOnce ||
            Shape.ABI == ABI::Async);
     assert(NewF && "need existing function for continuation");
@@ -74,22 +77,26 @@ class BaseCloner {
 
 public:
   BaseCloner(Function &OrigF, const Twine &Suffix, coro::Shape &Shape,
-             CloneKind FKind, TargetTransformInfo &TTI)
+             CloneKind FKind, TargetTransformInfo &TTI,
+             const MetadataSetTy &CommonDebugInfo)
       : OrigF(OrigF), Suffix(Suffix), Shape(Shape), FKind(FKind),
-        Builder(OrigF.getContext()), TTI(TTI) {}
+        Builder(OrigF.getContext()), TTI(TTI),
+        CommonDebugInfo(CommonDebugInfo) {}
 
   virtual ~BaseCloner() {}
 
   /// Create a clone for a continuation lowering.
   static Function *createClone(Function &OrigF, const Twine &Suffix,
                                coro::Shape &Shape, Function *NewF,
                                AnyCoroSuspendInst *ActiveSuspend,
-                               TargetTransformInfo &TTI) {
+                               TargetTransformInfo &TTI,
+                               const MetadataSetTy &CommonDebugInfo) {
     assert(Shape.ABI == ABI::Retcon || Shape.ABI == ABI::RetconOnce ||
            Shape.ABI == ABI::Async);
     TimeTraceScope FunctionScope("BaseCloner");
 
-    BaseCloner Cloner(OrigF, Suffix, Shape, NewF, ActiveSuspend, TTI);
+    BaseCloner Cloner(OrigF, Suffix, Shape, NewF, ActiveSuspend, TTI,
+                      CommonDebugInfo);
     Cloner.create();
     return Cloner.getFunction();
   }
@@ -129,20 +136,22 @@ class SwitchCloner : public BaseCloner {
 protected:
   /// Create a cloner for a switch lowering.
   SwitchCloner(Function &OrigF, const Twine &Suffix, coro::Shape &Shape,
-               CloneKind FKind, TargetTransformInfo &TTI)
-      : BaseCloner(OrigF, Suffix, Shape, FKind, TTI) {}
+               CloneKind FKind, TargetTransformInfo &TTI,
+               const MetadataSetTy &CommonDebugInfo)
+      : BaseCloner(OrigF, Suffix, Shape, FKind, TTI, CommonDebugInfo) {}
 
   void create() override;
 
 public:
   /// Create a clone for a switch lowering.
   static Function *createClone(Function &OrigF, const Twine &Suffix,
                                coro::Shape &Shape, CloneKind FKind,
-                               TargetTransformInfo &TTI) {
+                               TargetTransformInfo &TTI,
+                               const MetadataSetTy &CommonDebugInfo) {
     assert(Shape.ABI == ABI::Switch);
     TimeTraceScope FunctionScope("SwitchCloner");
 
-    SwitchCloner Cloner(OrigF, Suffix, Shape, FKind, TTI);
+    SwitchCloner Cloner(OrigF, Suffix, Shape, FKind, TTI, CommonDebugInfo);
     Cloner.create();
     return Cloner.getFunction();
   }

llvm/lib/Transforms/Coroutines/CoroSplit.cpp

@@ -43,6 +43,7 @@
 #include "llvm/IR/CallingConv.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/DataLayout.h"
+#include "llvm/IR/DebugInfo.h"
 #include "llvm/IR/DerivedTypes.h"
 #include "llvm/IR/Dominators.h"
 #include "llvm/IR/GlobalValue.h"
@@ -77,6 +78,24 @@ using namespace llvm;
 
 #define DEBUG_TYPE "coro-split"
 
+namespace {
+/// Collect (a known) subset of global debug info metadata potentially used by
+/// the function \p F.
+///
+/// This metadata set can be used to avoid cloning debug info not owned by \p F
+/// and is shared among all potential clones \p F.
+MetadataSetTy collectCommonDebugInfo(Function &F) {
+  TimeTraceScope FunctionScope("CollectCommonDebugInfo");
+
+  DebugInfoFinder DIFinder;
+  DISubprogram *SPClonedWithinModule = CollectDebugInfoForCloning(
+      F, CloneFunctionChangeType::LocalChangesOnly, DIFinder);
+
+  return FindDebugInfoToIdentityMap(CloneFunctionChangeType::LocalChangesOnly,
+                                    DIFinder, SPClonedWithinModule);
+}
+} // end anonymous namespace
+
 // FIXME:
 // Lower the intrinisc in CoroEarly phase if coroutine frame doesn't escape
 // and it is known that other transformations, for example, sanitizers
@@ -891,8 +910,11 @@ void coro::BaseCloner::create() {
   auto savedLinkage = NewF->getLinkage();
   NewF->setLinkage(llvm::GlobalValue::ExternalLinkage);
 
-  CloneFunctionInto(NewF, &OrigF, VMap,
-                    CloneFunctionChangeType::LocalChangesOnly, Returns);
+  CloneFunctionAttributesInto(NewF, &OrigF, VMap, false);
+  CloneFunctionMetadataInto(*NewF, OrigF, VMap, RF_None, nullptr, nullptr,
+                            &CommonDebugInfo);
+  CloneFunctionBodyInto(*NewF, OrigF, VMap, RF_None, Returns, "", nullptr,
+                        nullptr, nullptr, &CommonDebugInfo);
 
   auto &Context = NewF->getContext();
 
@@ -1374,16 +1396,21 @@ struct SwitchCoroutineSplitter {
                     TargetTransformInfo &TTI) {
     assert(Shape.ABI == coro::ABI::Switch);
 
+    MetadataSetTy CommonDebugInfo{collectCommonDebugInfo(F)};
+
     // Create a resume clone by cloning the body of the original function,
     // setting new entry block and replacing coro.suspend an appropriate value
     // to force resume or cleanup pass for every suspend point.
     createResumeEntryBlock(F, Shape);
     auto *ResumeClone = coro::SwitchCloner::createClone(
-        F, ".resume", Shape, coro::CloneKind::SwitchResume, TTI);
+        F, ".resume", Shape, coro::CloneKind::SwitchResume, TTI,
+        CommonDebugInfo);
     auto *DestroyClone = coro::SwitchCloner::createClone(
-        F, ".destroy", Shape, coro::CloneKind::SwitchUnwind, TTI);
+        F, ".destroy", Shape, coro::CloneKind::SwitchUnwind, TTI,
+        CommonDebugInfo);
     auto *CleanupClone = coro::SwitchCloner::createClone(
-        F, ".cleanup", Shape, coro::CloneKind::SwitchCleanup, TTI);
+        F, ".cleanup", Shape, coro::CloneKind::SwitchCleanup, TTI,
+        CommonDebugInfo);
 
     postSplitCleanup(*ResumeClone);
     postSplitCleanup(*DestroyClone);
@@ -1768,12 +1795,15 @@ void coro::AsyncABI::splitCoroutine(Function &F, coro::Shape &Shape,
   }
 
   assert(Clones.size() == Shape.CoroSuspends.size());
+
+  MetadataSetTy CommonDebugInfo{collectCommonDebugInfo(F)};
+
   for (auto [Idx, CS] : llvm::enumerate(Shape.CoroSuspends)) {
     auto *Suspend = CS;
     auto *Clone = Clones[Idx];
 
     coro::BaseCloner::createClone(F, "resume." + Twine(Idx), Shape, Clone,
-                                  Suspend, TTI);
+                                  Suspend, TTI, CommonDebugInfo);
   }
 }
 
@@ -1899,12 +1929,15 @@ void coro::AnyRetconABI::splitCoroutine(Function &F, coro::Shape &Shape,
   }
 
   assert(Clones.size() == Shape.CoroSuspends.size());
+
+  MetadataSetTy CommonDebugInfo{collectCommonDebugInfo(F)};
+
   for (auto [Idx, CS] : llvm::enumerate(Shape.CoroSuspends)) {
     auto Suspend = CS;
     auto Clone = Clones[Idx];
 
     coro::BaseCloner::createClone(F, "resume." + Twine(Idx), Shape, Clone,
-                                  Suspend, TTI);
+                                  Suspend, TTI, CommonDebugInfo);
   }
 }