Don't emit shadow copies for anonymous variables.

Switch statements generate at least one anonymous match variable per
case, which consumes both a lot of stack space and an explosion of
range extension depencies due to the way case statements are scoped.

rdar://problem/34326355

lib/IRGen/IRGenDebugInfo.cpp

@@ -1994,19 +1994,7 @@ void IRGenDebugInfoImpl::emitDbgIntrinsic(
     return;
   }
 
-  // If the storage is an instruction, insert the dbg.value directly after it.
-  if (auto *I = dyn_cast<llvm::Instruction>(Storage)) {
-    auto InsPt = std::next(I->getIterator());
-    auto E = I->getParent()->end();
-    while (InsPt != E && isa<llvm::PHINode>(&*InsPt))
-      ++InsPt;
-    if (InsPt != E) {
-      DBuilder.insertDbgValueIntrinsic(Storage, Var, Expr, DL, &*InsPt);
-      return;
-    }
-  }
-
-  // Otherwise just insert it at the current insertion point.
+  // Insert a dbg.value at the current insertion point.
   DBuilder.insertDbgValueIntrinsic(Storage, Var, Expr, DL, BB);
 }
 

lib/IRGen/IRGenSIL.cpp

@@ -578,13 +578,15 @@ public:
   }
 
   template <class DebugVarCarryingInst>
-  StringRef getVarName(DebugVarCarryingInst *i) {
+  StringRef getVarName(DebugVarCarryingInst *i, bool &IsAnonymous) {
     StringRef Name = i->getVarInfo().Name;
     // The $match variables generated by the type checker are not
     // guaranteed to be unique within their scope, but they have
     // unique VarDecls.
-    if ((Name.empty() || Name == "$match") && i->getDecl())
+    if ((Name.empty() || Name == "$match") && i->getDecl()) {
+      IsAnonymous = true;
       return getOrCreateAnonymousVarName(i->getDecl());
+    }
     return Name;
   }
 
@@ -665,15 +667,13 @@ public:
   /// register allocator doesn't elide the dbg.value intrinsic when
   /// register pressure is high.  There is a trade-off to this: With
   /// shadow copies, we lose the precise lifetime.
-  llvm::Value *emitShadowCopy(llvm::Value *Storage,
-                              const SILDebugScope *Scope,
-                              StringRef Name, unsigned ArgNo,
+  llvm::Value *emitShadowCopy(llvm::Value *Storage, const SILDebugScope *Scope,
+                              StringRef Name, unsigned ArgNo, bool IsAnonymous,
                               Alignment Align = Alignment(0)) {
     auto Ty = Storage->getType();
     // Never emit shadow copies when optimizing, or if already on the stack.
-    if (IGM.IRGen.Opts.shouldOptimize() ||
-        isa<llvm::AllocaInst>(Storage) ||
-        isa<llvm::UndefValue>(Storage) ||
+    if (IGM.IRGen.Opts.shouldOptimize() || IsAnonymous ||
+        isa<llvm::AllocaInst>(Storage) || isa<llvm::UndefValue>(Storage) ||
         Ty == IGM.RefCountedPtrTy) // No debug info is emitted for refcounts.
       return Storage;
 
@@ -701,16 +701,17 @@ public:
   }
 
   llvm::Value *emitShadowCopy(Address Storage, const SILDebugScope *Scope,
-                              StringRef Name, unsigned ArgNo) {
-    return emitShadowCopy(Storage.getAddress(), Scope, Name, ArgNo,
+                              StringRef Name, unsigned ArgNo,
+                              bool IsAnonymous) {
+    return emitShadowCopy(Storage.getAddress(), Scope, Name, ArgNo, IsAnonymous,
                           Storage.getAlignment());
   }
 
   void emitShadowCopy(ArrayRef<llvm::Value *> vals, const SILDebugScope *Scope,
-                      StringRef Name, unsigned ArgNo,
+                      StringRef Name, unsigned ArgNo, bool IsAnonymous,
                       llvm::SmallVectorImpl<llvm::Value *> &copy) {
     // Only do this at -O0.
-    if (IGM.IRGen.Opts.shouldOptimize()) {
+    if (IGM.IRGen.Opts.shouldOptimize() || IsAnonymous) {
       copy.append(vals.begin(), vals.end());
       return;
     }
@@ -718,7 +719,7 @@ public:
     // Single or empty values.
     if (vals.size() <= 1) {
       for (auto val : vals)
-        copy.push_back(emitShadowCopy(val, Scope, Name, ArgNo));
+        copy.push_back(emitShadowCopy(val, Scope, Name, ArgNo, IsAnonymous));
       return;
     }
 
@@ -3435,7 +3436,7 @@ void IRGenSILFunction::emitErrorResultVar(SILResultInfo ErrorInfo,
   auto ErrorResultSlot = getErrorResultSlot(IGM.silConv.getSILType(ErrorInfo));
   SILDebugVariable Var = DbgValue->getVarInfo();
   auto Storage = emitShadowCopy(ErrorResultSlot.getAddress(), getDebugScope(),
-                                Var.Name, Var.ArgNo);
+                                Var.Name, Var.ArgNo, false);
   DebugTypeInfo DTI(nullptr, nullptr, ErrorInfo.getType(),
                     ErrorResultSlot->getType(), IGM.getPointerSize(),
                     IGM.getPointerAlignment(), true);
@@ -3460,7 +3461,8 @@ void IRGenSILFunction::visitDebugValueInst(DebugValueInst *i) {
     return;
   }
 
-  StringRef Name = getVarName(i);
+  bool IsAnonymous = false;
+  StringRef Name = getVarName(i, IsAnonymous);
   DebugTypeInfo DbgTy;
   SILType SILTy = SILVal->getType();
   auto RealTy = SILVal->getType().getSwiftRValueType();
@@ -3481,7 +3483,8 @@ void IRGenSILFunction::visitDebugValueInst(DebugValueInst *i) {
   llvm::SmallVector<llvm::Value *, 8> Copy; 
   Explosion e = getLoweredExplosion(SILVal);
   unsigned ArgNo = i->getVarInfo().ArgNo;
-  emitShadowCopy(e.claimAll(), i->getDebugScope(), Name, ArgNo, Copy);
+  emitShadowCopy(e.claimAll(), i->getDebugScope(), Name, ArgNo, IsAnonymous,
+                 Copy);
   emitDebugVariableDeclaration(Copy, DbgTy, SILTy, i->getDebugScope(),
                                i->getDecl(), Name, ArgNo);
 }
@@ -3497,7 +3500,8 @@ void IRGenSILFunction::visitDebugValueAddrInst(DebugValueAddrInst *i) {
   if (isa<SILUndef>(SILVal))
     return;
 
-  StringRef Name = getVarName(i);
+  bool IsAnonymous = false;
+  StringRef Name = getVarName(i, IsAnonymous);
   auto Addr = getLoweredAddress(SILVal).getAddress();
   SILType SILTy = SILVal->getType();
   auto RealType = SILTy.getSwiftRValueType();
@@ -3519,7 +3523,7 @@ void IRGenSILFunction::visitDebugValueAddrInst(DebugValueAddrInst *i) {
   // intrinsic.
   unsigned ArgNo = i->getVarInfo().ArgNo;
   emitDebugVariableDeclaration(
-      emitShadowCopy(Addr, i->getDebugScope(), Name, ArgNo), DbgTy,
+      emitShadowCopy(Addr, i->getDebugScope(), Name, ArgNo, IsAnonymous), DbgTy,
       SILType(), i->getDebugScope(), Decl, Name, ArgNo,
       DbgTy.isImplicitlyIndirect() ? DirectValue : IndirectValue);
 }
@@ -3736,7 +3740,8 @@ void IRGenSILFunction::emitDebugInfoForAllocStack(AllocStackInst *i,
     auto DbgTy = DebugTypeInfo::getLocalVariable(
         CurSILFn->getDeclContext(), CurSILFn->getGenericEnvironment(), Decl,
         RealType, type, false);
-    StringRef Name = getVarName(i);
+    bool IsAnonymous = false;
+    StringRef Name = getVarName(i, IsAnonymous);
     if (auto DS = i->getDebugScope())
       emitDebugVariableDeclaration(addr, DbgTy, SILTy, DS, Decl, Name,
                                    i->getVarInfo().ArgNo);
@@ -3751,7 +3756,8 @@ void IRGenSILFunction::visitAllocStackInst(swift::AllocStackInst *i) {
   StringRef dbgname;
 # ifndef NDEBUG
   // If this is a DEBUG build, use pretty names for the LLVM IR.
-  dbgname = getVarName(i);
+  bool IsAnonymous = false;
+  dbgname = getVarName(i, IsAnonymous);
 # endif
 
   (void) Decl;
@@ -3888,8 +3894,9 @@ void IRGenSILFunction::visitAllocBoxInst(swift::AllocBoxInst *i) {
                                       ->getFieldType(IGM.getSILModule(), 0));
 
   // Derive name from SIL location.
+  bool IsAnonymous = false;
   VarDecl *Decl = i->getDecl();
-  StringRef Name = getVarName(i);
+  StringRef Name = getVarName(i, IsAnonymous);
   StringRef DbgName =
 # ifndef NDEBUG
     // If this is a DEBUG build, use pretty names for the LLVM IR.
@@ -3928,7 +3935,8 @@ void IRGenSILFunction::visitAllocBoxInst(swift::AllocBoxInst *i) {
 
     IGM.DebugInfo->emitVariableDeclaration(
         Builder,
-        emitShadowCopy(boxWithAddr.getAddress(), i->getDebugScope(), Name, 0),
+        emitShadowCopy(boxWithAddr.getAddress(), i->getDebugScope(), Name, 0,
+                       IsAnonymous),
         DbgTy, i->getDebugScope(), Decl, Name, 0,
         DbgTy.isImplicitlyIndirect() ? DirectValue : IndirectValue);
   }

test/DebugInfo/anonymous.swift

@@ -1,9 +1,9 @@
 // RUN: %target-swift-frontend -primary-file %s -emit-ir -g -o - | %FileCheck %s
 
+// CHECK: !DILocalVariable(name: "x4", arg: 4
 // CHECK: !DILocalVariable(name: "_0", arg: 1
 // CHECK: !DILocalVariable(name: "_1", arg: 2
 // CHECK: !DILocalVariable(name: "_2", arg: 3
-// CHECK: !DILocalVariable(name: "x4", arg: 4
 
 public func fourth<T>(_: T, _: T, _: T, x4 : T) -> T {
   return x4

test/DebugInfo/patternvars.swift

@@ -31,27 +31,28 @@ public func mangle(s: [UnicodeScalar]) -> [UnicodeScalar] {
 
 // The patterns in the first case statement each define an anonymous variable,
 // which shares the storage with the expression in the switch statement. Make
-// sure we only emit live range extensions for the storage once per basic block.
+// sure we emit a dbg.value once per basic block.
 
 // CHECK: define {{.*}}@_T011patternvars6mangleSayAA13UnicodeScalarVGAE1s_tFA2DcfU_
-// CHECK: call void asm sideeffect "", "r"
-// CHECK-NOT: call void asm sideeffect "", "r"
-// CHECK: br {{.*}}label
-// CHECK: call void asm sideeffect "", "r"
-// CHECK-NOT: call void asm sideeffect "", "r"
-// CHECK: br {{.*}}label
-// CHECK: call void asm sideeffect "", "r"
-// CHECK-NOT: call void asm sideeffect "", "r"
-// CHECK: br {{.*}}label
-// CHECK: call void asm sideeffect "", "r"
-// CHECK-NOT: call void asm sideeffect "", "r"
-// CHECK: br {{.*}}label
-// CHECK: call void asm sideeffect "", "r"
-// CHECK-NOT: call void asm sideeffect "", "r"
-// CHECK: br {{.*}}label
-// CHECK: call void asm sideeffect "", "r"
-// CHECK-NOT: call void asm sideeffect "", "r"
-// CHECK: br {{.*}}label
-// CHECK: call void asm sideeffect "", "r"
-// CHECK-NOT: call void asm sideeffect "", "r"
-// CHECK: br {{.*}}label
+// CHECK: %[[VAL:[0-9]+]] = call swiftcc i32 @_T011patternvars13UnicodeScalarV5values6UInt32Vvg(i32 %0)
+// CHECK-NEXT:  call void @llvm.dbg.value(metadata i32 %[[VAL]]
+// CHECK:       ; <label>
+// CHECK:       call void @llvm.dbg.value(metadata i32 %[[VAL]]
+// CHECK-NOT:   call void @llvm.dbg.value
+// CHECK-NOT:   call void asm sideeffect "", "r"
+
+// CHECK:       ; <label>
+// CHECK:       call void @llvm.dbg.value(metadata i32 %[[VAL]]
+// CHECK-NOT:   call void @llvm.dbg.value
+// CHECK-NOT:   call void asm sideeffect "", "r"
+
+// CHECK:       ; <label>
+// CHECK:       call void @llvm.dbg.value(metadata i32 %[[VAL]]
+// CHECK-NOT:   call void @llvm.dbg.value
+// CHECK-NOT:   call void asm sideeffect "", "r"
+
+// CHECK:       ; <label>
+// CHECK:       call void @llvm.dbg.value(metadata i32 %[[VAL]]
+// CHECK-NOT:   call void @llvm.dbg.value
+// CHECK-NOT:   call void asm sideeffect "", "r"
+