Salvage debug info for function arguments in coro-split funclets.

adrian-prantl · adrian-prantl · commit 0554541b4454 · 2021-01-26T15:01:26.000-08:00
This patch improves the availability for variables stored in the coroutine frame by emitting an alloca to hold the pointer to the frame object and rewriting dbg.declare intrinsics to point inside the frame object using salvaged DIExpressions. Finally, a new alloca is created in the funclet to hold the FramePtr pointer to ensure that it is available throughout the entire function at -O0. This path also effectively reverts D90772. The testcase updates highlight nicely how every removed CHECK for a dbg.value is preceded by a new CHECK for a dbg.declare. Thanks to JunMa, Yifeng, and Bruno for their thoughtful reviews! Differential Revision: https://reviews.llvm.org/D93497 rdar://71866936
diff --git a/llvm/lib/Transforms/Coroutines/CoroFrame.cpp b/llvm/lib/Transforms/Coroutines/CoroFrame.cpp
@@ -1104,6 +1104,7 @@ static Instruction *insertSpills(const FrameDataInfo &FrameData,
   auto *FramePtr =
       cast<Instruction>(Builder.CreateBitCast(CB, FramePtrTy, "FramePtr"));
   DominatorTree DT(*CB->getFunction());
+  SmallDenseMap<llvm::Value *, llvm::AllocaInst *, 4> DbgPtrAllocaCache;
 
   // Create a GEP with the given index into the coroutine frame for the original
   // value Orig. Appends an extra 0 index for array-allocas, preserving the
@@ -1209,6 +1210,21 @@ static Instruction *insertSpills(const FrameDataInfo &FrameData,
         CurrentReload = Builder.CreateLoad(
             FrameTy->getElementType(FrameData.getFieldIndex(E.first)), GEP,
             E.first->getName() + Twine(".reload"));
+
+        TinyPtrVector<DbgDeclareInst *> DIs = FindDbgDeclareUses(Def);
+        for (DbgDeclareInst *DDI : DIs) {
+          bool AllowUnresolved = false;
+          // This dbg.declare is preserved for all coro-split function
+          // fragments. It will be unreachable in the main function, and
+          // processed by coro::salvageDebugInfo() by CoroCloner.
+          DIBuilder(*CurrentBlock->getParent()->getParent(), AllowUnresolved)
+              .insertDeclare(CurrentReload, DDI->getVariable(),
+                             DDI->getExpression(), DDI->getDebugLoc(),
+                             &*Builder.GetInsertPoint());
+          // This dbg.declare is for the main function entry point.  It
+          // will be deleted in all coro-split functions.
+          coro::salvageDebugInfo(DbgPtrAllocaCache, DDI);
+        }
       }
 
       // If we have a single edge PHINode, remove it and replace it with a
@@ -1276,50 +1292,18 @@ static Instruction *insertSpills(const FrameDataInfo &FrameData,
 
     SmallPtrSet<BasicBlock *, 4> SeenDbgBBs;
     TinyPtrVector<DbgDeclareInst *> DIs = FindDbgDeclareUses(Alloca);
-    DIBuilder DIB(*Alloca->getModule(), /*AllowUnresolved*/ false);
-    Instruction *FirstDbgDecl = nullptr;
-
-    if (!DIs.empty()) {
-      FirstDbgDecl = DIB.insertDeclare(G, DIs.front()->getVariable(),
-                                       DIs.front()->getExpression(),
-                                       DIs.front()->getDebugLoc(), DIs.front());
-      SeenDbgBBs.insert(DIs.front()->getParent());
-    }
+    if (!DIs.empty())
+      DIBuilder(*Alloca->getModule(),
+                /*AllowUnresolved*/ false)
+          .insertDeclare(G, DIs.front()->getVariable(),
+                         DIs.front()->getExpression(),
+                         DIs.front()->getDebugLoc(), DIs.front());
     for (auto *DI : FindDbgDeclareUses(Alloca))
       DI->eraseFromParent();
     replaceDbgUsesWithUndef(Alloca);
 
-    for (Instruction *I : UsersToUpdate) {
+    for (Instruction *I : UsersToUpdate)
       I->replaceUsesOfWith(Alloca, G);
-
-      // After cloning, transformations might not guarantee that all uses
-      // of this alloca are dominated by the already existing dbg.declare's,
-      // compromising the debug quality. Instead of writing another
-      // transformation to patch each clone, go ahead and early populate
-      // basic blocks that use such allocas with more debug info.
-      if (SeenDbgBBs.count(I->getParent()))
-        continue;
-
-      // If there isn't a prior dbg.declare for this alloca, it probably
-      // means the state hasn't changed prior to one of the relevant suspend
-      // point for this frame access.
-      if (!FirstDbgDecl)
-        continue;
-
-      // These instructions are all dominated by the alloca, insert the
-      // dbg.value in the beginning of the BB to enhance debugging
-      // experience and allow values to be inspected as early as possible.
-      // Prefer dbg.value over dbg.declare since it better sets expectations
-      // that control flow can be later changed by other passes.
-      auto *DI = cast<DbgDeclareInst>(FirstDbgDecl);
-      BasicBlock *CurrentBlock = I->getParent();
-      auto *DerefExpr =
-          DIExpression::append(DI->getExpression(), dwarf::DW_OP_deref);
-      DIB.insertDbgValueIntrinsic(G, DI->getVariable(), DerefExpr,
-                                  DI->getDebugLoc(),
-                                  &*CurrentBlock->getFirstInsertionPt());
-      SeenDbgBBs.insert(CurrentBlock);
-    }
   }
   Builder.SetInsertPoint(FramePtr->getNextNode());
   for (const auto &A : FrameData.Allocas) {
@@ -2172,6 +2156,58 @@ static void collectFrameAllocas(Function &F, coro::Shape &Shape,
   }
 }
 
+void coro::salvageDebugInfo(
+    SmallDenseMap<llvm::Value *, llvm::AllocaInst *, 4> &DbgPtrAllocaCache,
+    DbgDeclareInst *DDI, bool LoadFromFramePtr) {
+  Function *F = DDI->getFunction();
+  IRBuilder<> Builder(F->getContext());
+  auto InsertPt = F->getEntryBlock().getFirstInsertionPt();
+  while (isa<IntrinsicInst>(InsertPt))
+    ++InsertPt;
+  Builder.SetInsertPoint(&F->getEntryBlock(), InsertPt);
+  DIExpression *Expr = DDI->getExpression();
+  // Follow the pointer arithmetic all the way to the incoming
+  // function argument and convert into a DIExpression.
+  Value *Storage = DDI->getAddress();
+  while (Storage) {
+    if (auto *LdInst = dyn_cast<LoadInst>(Storage)) {
+      Storage = LdInst->getOperand(0);
+    } else if (auto *StInst = dyn_cast<StoreInst>(Storage)) {
+      Storage = StInst->getOperand(0);
+    } else if (auto *GEPInst = dyn_cast<GetElementPtrInst>(Storage)) {
+      Expr = llvm::salvageDebugInfoImpl(*GEPInst, Expr,
+                                        /*WithStackValue=*/false);
+      Storage = GEPInst->getOperand(0);
+    } else if (auto *BCInst = dyn_cast<llvm::BitCastInst>(Storage))
+      Storage = BCInst->getOperand(0);
+    else
+      break;
+  }
+  // Store a pointer to the coroutine frame object in an alloca so it
+  // is available throughout the function when producing unoptimized
+  // code. Extending the lifetime this way is correct because the
+  // variable has been declared by a dbg.declare intrinsic.
+  if (auto Arg = dyn_cast_or_null<llvm::Argument>(Storage)) {
+    auto &Cached = DbgPtrAllocaCache[Storage];
+    if (!Cached) {
+      Cached = Builder.CreateAlloca(Storage->getType(), 0, nullptr,
+                                    Arg->getName() + ".debug");
+      Builder.CreateStore(Storage, Cached);
+    }
+    Storage = Cached;
+  }
+  // The FramePtr object adds one extra layer of indirection that
+  // needs to be unwrapped.
+  if (LoadFromFramePtr)
+    Expr = DIExpression::prepend(Expr, DIExpression::DerefBefore);
+  auto &VMContext = DDI->getFunction()->getContext();
+  DDI->setOperand(
+      0, MetadataAsValue::get(VMContext, ValueAsMetadata::get(Storage)));
+  DDI->setOperand(2, MetadataAsValue::get(VMContext, Expr));
+  if (auto *InsertPt = dyn_cast_or_null<Instruction>(Storage))
+    DDI->moveAfter(InsertPt);
+}
+
 void coro::buildCoroutineFrame(Function &F, Shape &Shape) {
   eliminateSwiftError(F, Shape);
 
diff --git a/llvm/lib/Transforms/Coroutines/CoroInternal.h b/llvm/lib/Transforms/Coroutines/CoroInternal.h
@@ -50,6 +50,11 @@ bool declaresIntrinsics(const Module &M,
 void replaceCoroFree(CoroIdInst *CoroId, bool Elide);
 void updateCallGraph(Function &Caller, ArrayRef<Function *> Funcs,
                      CallGraph &CG, CallGraphSCC &SCC);
+/// Recover a dbg.declare prepared by the frontend and emit an alloca
+/// holding a pointer to the coroutine frame.
+void salvageDebugInfo(
+    SmallDenseMap<llvm::Value *, llvm::AllocaInst *, 4> &DbgPtrAllocaCache,
+    DbgDeclareInst *DDI, bool LoadFromCoroFrame = false);
 
 // Keeps data and helper functions for lowering coroutine intrinsics.
 struct LowererBase {
diff --git a/llvm/lib/Transforms/Coroutines/CoroSplit.cpp b/llvm/lib/Transforms/Coroutines/CoroSplit.cpp
@@ -158,6 +158,7 @@ class CoroCloner {
   void replaceCoroSuspends();
   void replaceCoroEnds();
   void replaceSwiftErrorOps();
+  void salvageDebugInfo();
   void handleFinalSuspend();
 };
 
@@ -631,6 +632,39 @@ void CoroCloner::replaceSwiftErrorOps() {
   ::replaceSwiftErrorOps(*NewF, Shape, &VMap);
 }
 
+void CoroCloner::salvageDebugInfo() {
+  SmallVector<DbgDeclareInst *, 8> Worklist;
+  SmallDenseMap<llvm::Value *, llvm::AllocaInst *, 4> DbgPtrAllocaCache;
+  for (auto &BB : *NewF)
+    for (auto &I : BB)
+      if (auto *DDI = dyn_cast<DbgDeclareInst>(&I))
+        Worklist.push_back(DDI);
+  for (DbgDeclareInst *DDI : Worklist) {
+    // This is a heuristic that detects declares left by CoroFrame.
+    bool LoadFromFramePtr = !isa<AllocaInst>(DDI->getAddress());
+    coro::salvageDebugInfo(DbgPtrAllocaCache, DDI, LoadFromFramePtr);
+  }
+  // Remove all salvaged dbg.declare intrinsics that became
+  // either unreachable or stale due to the CoroSplit transformation.
+  auto IsUnreachableBlock = [&](BasicBlock *BB) {
+    return BB->hasNPredecessors(0) && BB != &NewF->getEntryBlock();
+  };
+  for (DbgDeclareInst *DDI : Worklist) {
+    if (IsUnreachableBlock(DDI->getParent()))
+      DDI->eraseFromParent();
+    else if (auto *Alloca = dyn_cast_or_null<AllocaInst>(DDI->getAddress())) {
+      // Count all non-debuginfo uses in reachable blocks.
+      unsigned Uses = 0;
+      for (auto *User : DDI->getAddress()->users())
+        if (auto *I = dyn_cast<Instruction>(User))
+          if (!isa<AllocaInst>(I) && !IsUnreachableBlock(I->getParent()))
+            ++Uses;
+      if (!Uses)
+        DDI->eraseFromParent();
+    }
+  }
+}
+
 void CoroCloner::replaceEntryBlock() {
   // In the original function, the AllocaSpillBlock is a block immediately
   // following the allocation of the frame object which defines GEPs for
@@ -904,6 +938,9 @@ void CoroCloner::create() {
   // Remove coro.end intrinsics.
   replaceCoroEnds();
 
+  // Salvage debug info that points into the coroutine frame.
+  salvageDebugInfo();
+
   // Eliminate coro.free from the clones, replacing it with 'null' in cleanup,
   // to suppress deallocation code.
   if (Shape.ABI == coro::ABI::Switch)
diff --git a/llvm/test/Transforms/Coroutines/coro-debug-frame-variable.ll b/llvm/test/Transforms/Coroutines/coro-debug-frame-variable.ll
@@ -37,22 +37,18 @@
 ; CHECK:         call void @llvm.dbg.declare(metadata i32* [[IGEP]], metadata ![[IVAR:[0-9]+]], metadata !DIExpression()), !dbg ![[IDBGLOC:[0-9]+]]
 ; CHECK:         call void @llvm.dbg.declare(metadata [10 x i32]* [[XGEP]], metadata ![[XVAR:[0-9]+]], metadata !DIExpression()), !dbg ![[IDBGLOC]]
 ; CHECK:       await.ready:
-; CHECK:         call void @llvm.dbg.value(metadata [10 x i32]* [[XGEP]], metadata ![[XVAR]], metadata !DIExpression(DW_OP_deref)), !dbg ![[IDBGLOC]]
-; CHECK:         call void @llvm.dbg.value(metadata i32* [[IGEP]], metadata ![[IVAR]], metadata !DIExpression(DW_OP_deref)), !dbg ![[IDBGLOC]]
 ; CHECK:         call void @llvm.dbg.declare(metadata i32* %j, metadata ![[JVAR:[0-9]+]], metadata !DIExpression()), !dbg ![[JDBGLOC:[0-9]+]]
 ;
 ; CHECK-LABEL: define internal fastcc void @f.resume({{.*}}) {
 ; CHECK:       entry.resume:
-; CHECK:         %j = alloca i32, align 4
-; CHECK:         [[IGEP_RESUME:%.+]] = getelementptr inbounds %f.Frame, %f.Frame* %FramePtr, i32 0, i32 4
-; CHECK:         [[XGEP_RESUME:%.+]] = getelementptr inbounds %f.Frame, %f.Frame* %FramePtr, i32 0, i32 6
+; CHECK-NEXT:    %[[DBG_PTR:.*]] = alloca %f.Frame*
+; CHECK-NEXT:    call void @llvm.dbg.declare(metadata %f.Frame** %[[DBG_PTR]], metadata ![[XVAR_RESUME:[0-9]+]],   metadata !DIExpression(DW_OP_deref, DW_OP_plus_uconst, 32)), !dbg
+; CHECK-NEXT:    call void @llvm.dbg.declare(metadata %f.Frame** %[[DBG_PTR]], metadata ![[IVAR_RESUME:[0-9]+]], metadata !DIExpression(DW_OP_deref, DW_OP_plus_uconst, 20)), !dbg ![[IDBGLOC_RESUME:[0-9]+]]
+; CHECK-NEXT:    store %f.Frame* {{.*}}, %f.Frame** %[[DBG_PTR]]
+; CHECK:         %[[J:.*]] = alloca i32, align 4
+; CHECK-NEXT:    call void @llvm.dbg.declare(metadata i32* %[[J]], metadata ![[JVAR_RESUME:[0-9]+]], metadata !DIExpression()), !dbg ![[JDBGLOC_RESUME:[0-9]+]]
 ; CHECK:       init.ready:
-; CHECK:         call void @llvm.dbg.declare(metadata i32* [[IGEP_RESUME]], metadata ![[IVAR_RESUME:[0-9]+]], metadata !DIExpression()), !dbg ![[IDBGLOC_RESUME:[0-9]+]]
-; CHECK:         call void @llvm.dbg.declare(metadata [10 x i32]* [[XGEP_RESUME]], metadata ![[XVAR_RESUME:[0-9]+]], metadata !DIExpression()), !dbg ![[IDBGLOC_RESUME]]
 ; CHECK:       await.ready:
-; CHECK:         call void @llvm.dbg.value(metadata [10 x i32]* [[XGEP_RESUME]], metadata ![[XVAR_RESUME]], metadata !DIExpression(DW_OP_deref)), !dbg ![[IDBGLOC_RESUME]]
-; CHECK:         call void @llvm.dbg.value(metadata i32* [[IGEP_RESUME]], metadata ![[IVAR_RESUME]], metadata !DIExpression(DW_OP_deref)), !dbg ![[IDBGLOC_RESUME]]
-; CHECK:         call void @llvm.dbg.declare(metadata i32* %j, metadata ![[JVAR_RESUME:[0-9]+]], metadata !DIExpression()), !dbg ![[JDBGLOC_RESUME:[0-9]+]]
 ;
 ; CHECK: ![[IVAR]] = !DILocalVariable(name: "i"
 ; CHECK: ![[SCOPE:[0-9]+]] = distinct !DILexicalBlock(scope: !8, file: !1, line: 23, column: 12)
@@ -61,10 +57,10 @@
 ; CHECK: ![[JVAR]] = !DILocalVariable(name: "j"
 ; CHECK: ![[JDBGLOC]] = !DILocation(line: 32, column: 7, scope: ![[SCOPE]])
 
-; CHECK: ![[IVAR_RESUME]] = !DILocalVariable(name: "i"
-; CHECK: ![[RESUME_SCOPE:[0-9]+]] = distinct !DILexicalBlock(scope: !8, file: !1, line: 23, column: 12)
-; CHECK: ![[IDBGLOC_RESUME]] = !DILocation(line: 24, column: 7, scope: ![[RESUME_SCOPE]])
 ; CHECK: ![[XVAR_RESUME]] = !DILocalVariable(name: "x"
+; CHECK: ![[IDBGLOC_RESUME]] = !DILocation(line: 24, column: 7, scope: ![[RESUME_SCOPE:[0-9]+]])
+; CHECK: ![[RESUME_SCOPE]] = distinct !DILexicalBlock(scope: !8, file: !1, line: 23, column: 12)
+; CHECK: ![[IVAR_RESUME]] = !DILocalVariable(name: "i"
 ; CHECK: ![[JVAR_RESUME]] = !DILocalVariable(name: "j"
 ; CHECK: ![[JDBGLOC_RESUME]] = !DILocation(line: 32, column: 7, scope: ![[RESUME_SCOPE]])
 define void @f() {
diff --git a/llvm/test/Transforms/Coroutines/coro-debug.ll b/llvm/test/Transforms/Coroutines/coro-debug.ll
@@ -130,15 +130,20 @@ attributes #7 = { noduplicate }
 ; CHECK: define i8* @f(i32 %x) #0 !dbg ![[ORIG:[0-9]+]]
 ; CHECK: define internal fastcc void @f.resume(%f.Frame* noalias nonnull align 8 dereferenceable(32) %FramePtr) #0 !dbg ![[RESUME:[0-9]+]]
 ; CHECK: entry.resume:
+; CHECK: %[[DBG_PTR:.*]] = alloca %f.Frame*
+; CHECK: call void @llvm.dbg.declare(metadata %f.Frame** %[[DBG_PTR]], metadata ![[RESUME_COROHDL:[0-9]+]], metadata !DIExpression(DW_OP_deref, DW_OP_plus_uconst,
+; CHECK: call void @llvm.dbg.declare(metadata %f.Frame** %[[DBG_PTR]], metadata ![[RESUME_X:[0-9]+]], metadata !DIExpression(DW_OP_deref, DW_OP_plus_uconst,
+; CHECK: store %f.Frame* {{.*}}, %f.Frame** %[[DBG_PTR]]
+; CHECK-NOT: alloca %struct.test*
 ; CHECK: call void @coro.devirt.trigger(i8* null)
-; CHECK: call void @llvm.dbg.declare(metadata i32* %x.addr.reload.addr, metadata ![[RESUME_VAR:[0-9]+]]
 ; CHECK: define internal fastcc void @f.destroy(%f.Frame* noalias nonnull align 8 dereferenceable(32) %FramePtr) #0 !dbg ![[DESTROY:[0-9]+]]
 ; CHECK: define internal fastcc void @f.cleanup(%f.Frame* noalias nonnull align 8 dereferenceable(32) %FramePtr) #0 !dbg ![[CLEANUP:[0-9]+]]
 
 ; CHECK: ![[ORIG]] = distinct !DISubprogram(name: "f", linkageName: "flink"
 
 ; CHECK: ![[RESUME]] = distinct !DISubprogram(name: "f", linkageName: "flink"
-; CHECK: ![[RESUME_VAR]] = !DILocalVariable(name: "x", arg: 1, scope: ![[RESUME]]
+; CHECK: ![[RESUME_COROHDL]] = !DILocalVariable(name: "coro_hdl", scope: ![[RESUME]]
+; CHECK: ![[RESUME_X]] = !DILocalVariable(name: "x", arg: 1, scope: ![[RESUME]]
 
 ; CHECK: ![[DESTROY]] = distinct !DISubprogram(name: "f", linkageName: "flink"
 
