Emit lifetime.start / lifetime.end markers for unnamed temporary objects.

This will give more information to the optimizers so that they can reuse stack slots.

llvm-svn: 213576

3 files changed, 78 insertions, 24 deletions

diff --git a/clang/lib/CodeGen/CGDecl.cpp b/clang/lib/CodeGen/CGDecl.cpp
index 91f80419304..9c8882decc6 100644
--- a/clang/lib/CodeGen/CGDecl.cpp
+++ b/clang/lib/CodeGen/CGDecl.cpp
@@ -468,22 +468,6 @@ namespace {
       CGF.EmitCall(FnInfo, CleanupFn, ReturnValueSlot(), Args);
     }
   };
-
-  /// A cleanup to call @llvm.lifetime.end.
-  class CallLifetimeEnd : public EHScopeStack::Cleanup {
-    llvm::Value *Addr;
-    llvm::Value *Size;
-  public:
-    CallLifetimeEnd(llvm::Value *addr, llvm::Value *size)
-      : Addr(addr), Size(size) {}
-
-    void Emit(CodeGenFunction &CGF, Flags flags) override {
-      llvm::Value *castAddr = CGF.Builder.CreateBitCast(Addr, CGF.Int8PtrTy);
-      CGF.Builder.CreateCall2(CGF.CGM.getLLVMLifetimeEndFn(),
-                              Size, castAddr)
-        ->setDoesNotThrow();
-    }
-  };
 }
 
 /// EmitAutoVarWithLifetime - Does the setup required for an automatic
@@ -802,10 +786,9 @@ static bool shouldUseMemSetPlusStoresToInitialize(llvm::Constant *Init,
 }
 
 /// Should we use the LLVM lifetime intrinsics for the given local variable?
-static bool shouldUseLifetimeMarkers(CodeGenFunction &CGF, const VarDecl &D,
-                                     unsigned Size) {
+bool CodeGenFunction::shouldUseLifetimeMarkers(unsigned Size) const {
   // For now, only in optimized builds.
-  if (CGF.CGM.getCodeGenOpts().OptimizationLevel == 0)
+  if (CGM.getCodeGenOpts().OptimizationLevel == 0)
     return false;
 
   // Limit the size of marked objects to 32 bytes. We don't want to increase
@@ -815,7 +798,6 @@ static bool shouldUseLifetimeMarkers(CodeGenFunction &CGF, const VarDecl &D,
   return Size > SizeThreshold;
 }
 
-
 /// EmitAutoVarDecl - Emit code and set up an entry in LocalDeclMap for a
 /// variable declaration with auto, register, or no storage class specifier.
 /// These turn into simple stack objects, or GlobalValues depending on target.
@@ -825,6 +807,18 @@ void CodeGenFunction::EmitAutoVarDecl(const VarDecl &D) {
   EmitAutoVarCleanups(emission);
 }
 
+void CodeGenFunction::EmitLifetimeStart(llvm::Value *Size, llvm::Value *Addr) {
+  llvm::Value *castAddr = Builder.CreateBitCast(Addr, Int8PtrTy);
+  Builder.CreateCall2(CGM.getLLVMLifetimeStartFn(), Size, castAddr)
+      ->setDoesNotThrow();
+}
+
+void CodeGenFunction::EmitLifetimeEnd(llvm::Value *Size, llvm::Value *Addr) {
+  llvm::Value *castAddr = Builder.CreateBitCast(Addr, Int8PtrTy);
+  Builder.CreateCall2(CGM.getLLVMLifetimeEndFn(), Size, castAddr)
+      ->setDoesNotThrow();
+}
+
 /// EmitAutoVarAlloca - Emit the alloca and debug information for a
 /// local variable.  Does not emit initialization or destruction.
 CodeGenFunction::AutoVarEmission
@@ -920,13 +914,11 @@ CodeGenFunction::EmitAutoVarAlloca(const VarDecl &D) {
       // Emit a lifetime intrinsic if meaningful.  There's no point
       // in doing this if we don't have a valid insertion point (?).
       uint64_t size = CGM.getDataLayout().getTypeAllocSize(LTy);
-      if (HaveInsertPoint() && shouldUseLifetimeMarkers(*this, D, size)) {
+      if (HaveInsertPoint() && shouldUseLifetimeMarkers(size)) {
         llvm::Value *sizeV = llvm::ConstantInt::get(Int64Ty, size);
 
         emission.SizeForLifetimeMarkers = sizeV;
-        llvm::Value *castAddr = Builder.CreateBitCast(Alloc, Int8PtrTy);
-        Builder.CreateCall2(CGM.getLLVMLifetimeStartFn(), sizeV, castAddr)
-          ->setDoesNotThrow();
+        EmitLifetimeStart(sizeV, Alloc);
       } else {
         assert(!emission.useLifetimeMarkers());
       }
diff --git a/clang/lib/CodeGen/CGExpr.cpp b/clang/lib/CodeGen/CGExpr.cpp
index 512b323ba10..2c9c2f130e8 100644
--- a/clang/lib/CodeGen/CGExpr.cpp
+++ b/clang/lib/CodeGen/CGExpr.cpp
@@ -353,6 +353,17 @@ LValue CodeGenFunction::EmitMaterializeTemporaryExpr(
 
   // Create and initialize the reference temporary.
   llvm::Value *Object = createReferenceTemporary(*this, M, E);
+
+  uint64_t size =
+      CGM.getDataLayout().getTypeStoreSize(ConvertTypeForMem(E->getType()));
+  llvm::Value *sizeV = nullptr;
+  llvm::AllocaInst *Alloca = dyn_cast<llvm::AllocaInst>(Object);
+  bool useLifetimeMarkers = Alloca && shouldUseLifetimeMarkers(size);
+  if (useLifetimeMarkers) {
+    sizeV = llvm::ConstantInt::get(Int64Ty, size);
+    EmitLifetimeStart(sizeV, Object);
+  }
+
   if (auto *Var = dyn_cast<llvm::GlobalVariable>(Object)) {
     // If the temporary is a global and has a constant initializer, we may
     // have already initialized it.
@@ -363,6 +374,20 @@ LValue CodeGenFunction::EmitMaterializeTemporaryExpr(
   } else {
     EmitAnyExprToMem(E, Object, Qualifiers(), /*IsInit*/true);
   }
+
+  if (useLifetimeMarkers)
+    switch (M->getStorageDuration()) {
+    case SD_FullExpression:
+      EHStack.pushCleanup<CallLifetimeEnd>(NormalAndEHCleanup, Object, sizeV);
+      break;
+    case SD_Automatic:
+      pushCleanupAfterFullExpr<CallLifetimeEnd>(NormalAndEHCleanup, Object,
+                                                sizeV);
+      break;
+    default:
+      llvm_unreachable("unexpected storage duration for Lifetime markers");
+    }
+
   pushTemporaryCleanup(*this, M, E, Object);
 
   // Perform derived-to-base casts and/or field accesses, to get from the
diff --git a/clang/lib/CodeGen/CodeGenFunction.h b/clang/lib/CodeGen/CodeGenFunction.h
index 59cc30da42c..cd668e05afe 100644
--- a/clang/lib/CodeGen/CodeGenFunction.h
+++ b/clang/lib/CodeGen/CodeGenFunction.h
@@ -436,6 +436,23 @@ public:
     new (Buffer + sizeof(Header)) T(a0, a1, a2, a3);
   }
 
+  /// \brief Queue a cleanup to be pushed after finishing the current
+  /// full-expression.
+  template <class T, class A0, class A1>
+  void pushCleanupAfterFullExpr(CleanupKind Kind, A0 a0, A1 a1) {
+    assert(!isInConditionalBranch() && "can't defer conditional cleanup");
+
+    LifetimeExtendedCleanupHeader Header = { sizeof(T), Kind };
+
+    size_t OldSize = LifetimeExtendedCleanupStack.size();
+    LifetimeExtendedCleanupStack.resize(
+        LifetimeExtendedCleanupStack.size() + sizeof(Header) + Header.Size);
+
+    char *Buffer = &LifetimeExtendedCleanupStack[OldSize];
+    new (Buffer) LifetimeExtendedCleanupHeader(Header);
+    new (Buffer + sizeof(Header)) T(a0, a1);
+  }
+
   /// Set up the last cleaup that was pushed as a conditional
   /// full-expression cleanup.
   void initFullExprCleanup();
@@ -990,6 +1007,23 @@ private:
   void EmitOpenCLKernelMetadata(const FunctionDecl *FD, 
                                 llvm::Function *Fn);
 
+  /// Should we use the LLVM lifetime intrinsics for a local variable of the
+  /// given size in bytes ?
+  bool shouldUseLifetimeMarkers(unsigned Size) const;
+
+  /// A cleanup to call @llvm.lifetime.end.
+  class CallLifetimeEnd : public EHScopeStack::Cleanup {
+    llvm::Value *Addr;
+    llvm::Value *Size;
+  public:
+    CallLifetimeEnd(llvm::Value *addr, llvm::Value *size)
+      : Addr(addr), Size(size) {}
+
+    void Emit(CodeGenFunction &CGF, Flags flags) override {
+      CGF.EmitLifetimeEnd(Size, Addr);
+    }
+  };
+
 public:
   CodeGenFunction(CodeGenModule &cgm, bool suppressNewContext=false);
   ~CodeGenFunction();
@@ -1673,6 +1707,9 @@ public:
   void EmitCXXTemporary(const CXXTemporary *Temporary, QualType TempType,
                         llvm::Value *Ptr);
 
+  void EmitLifetimeStart(llvm::Value *Size, llvm::Value *Addr);
+  void EmitLifetimeEnd(llvm::Value *Size, llvm::Value *Addr);
+
   llvm::Value *EmitCXXNewExpr(const CXXNewExpr *E);
   void EmitCXXDeleteExpr(const CXXDeleteExpr *E);