From 42d314d1ba7fd02da1784c2a2e26e7a91a6ef1b4 Mon Sep 17 00:00:00 2001
From: "Arnaud A. de Grandmaison" <arnaud.degrandmaison@arm.com>
Date: Thu, 2 Oct 2014 12:19:51 +0000
Subject: 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
and reduce stack usage.

llvm-svn: 218865
---
 clang/lib/CodeGen/CGExpr.cpp | 38 +++++++++++++++++++++++++++-----------
 1 file changed, 27 insertions(+), 11 deletions(-)

(limited to 'clang/lib/CodeGen/CGExpr.cpp')

diff --git a/clang/lib/CodeGen/CGExpr.cpp b/clang/lib/CodeGen/CGExpr.cpp
index 4fe37546b60..7b26009a65e 100644
--- a/clang/lib/CodeGen/CGExpr.cpp
+++ b/clang/lib/CodeGen/CGExpr.cpp
@@ -173,9 +173,10 @@ void CodeGenFunction::EmitAnyExprToMem(const Expr *E,
   llvm_unreachable("bad evaluation kind");
 }
 
-static void
-pushTemporaryCleanup(CodeGenFunction &CGF, const MaterializeTemporaryExpr *M,
-                     const Expr *E, llvm::Value *ReferenceTemporary) {
+static void pushTemporaryCleanup(CodeGenFunction &CGF,
+                                 const MaterializeTemporaryExpr *M,
+                                 const Expr *E, llvm::Value *ReferenceTemporary,
+                                 llvm::Value *SizeForLifeTimeMarkers) {
   // Objective-C++ ARC:
   //   If we are binding a reference to a temporary that has ownership, we
   //   need to perform retain/release operations on the temporary.
@@ -242,6 +243,10 @@ pushTemporaryCleanup(CodeGenFunction &CGF, const MaterializeTemporaryExpr *M,
     }
   }
 
+  // Call @llvm.lifetime.end marker for the temporary.
+  CGF.pushLifetimeEndMarker(M->getStorageDuration(), ReferenceTemporary,
+                            SizeForLifeTimeMarkers);
+
   CXXDestructorDecl *ReferenceTemporaryDtor = nullptr;
   if (const RecordType *RT =
           E->getType()->getBaseElementTypeUnsafe()->getAs<RecordType>()) {
@@ -296,11 +301,18 @@ pushTemporaryCleanup(CodeGenFunction &CGF, const MaterializeTemporaryExpr *M,
 
 static llvm::Value *
 createReferenceTemporary(CodeGenFunction &CGF,
-                         const MaterializeTemporaryExpr *M, const Expr *Inner) {
+                         const MaterializeTemporaryExpr *M, const Expr *Inner,
+                         llvm::Value *&SizeForLifeTimeMarkers) {
+  SizeForLifeTimeMarkers = nullptr;
   switch (M->getStorageDuration()) {
   case SD_FullExpression:
-  case SD_Automatic:
-    return CGF.CreateMemTemp(Inner->getType(), "ref.tmp");
+  case SD_Automatic: {
+    llvm::Value *RefTemp = CGF.CreateMemTemp(Inner->getType(), "ref.tmp");
+    uint64_t TempSize = CGF.CGM.getDataLayout().getTypeStoreSize(
+        CGF.ConvertTypeForMem(Inner->getType()));
+    SizeForLifeTimeMarkers = CGF.EmitLifetimeStart(TempSize, RefTemp);
+    return RefTemp;
+  }
 
   case SD_Thread:
   case SD_Static:
@@ -321,7 +333,8 @@ LValue CodeGenFunction::EmitMaterializeTemporaryExpr(
       M->getType().getObjCLifetime() != Qualifiers::OCL_None &&
       M->getType().getObjCLifetime() != Qualifiers::OCL_ExplicitNone) {
     // FIXME: Fold this into the general case below.
-    llvm::Value *Object = createReferenceTemporary(*this, M, E);
+    llvm::Value *ObjectSize;
+    llvm::Value *Object = createReferenceTemporary(*this, M, E, ObjectSize);
     LValue RefTempDst = MakeAddrLValue(Object, M->getType());
 
     if (auto *Var = dyn_cast<llvm::GlobalVariable>(Object)) {
@@ -333,7 +346,7 @@ LValue CodeGenFunction::EmitMaterializeTemporaryExpr(
 
     EmitScalarInit(E, M->getExtendingDecl(), RefTempDst, false);
 
-    pushTemporaryCleanup(*this, M, E, Object);
+    pushTemporaryCleanup(*this, M, E, Object, ObjectSize);
     return RefTempDst;
   }
 
@@ -351,8 +364,10 @@ LValue CodeGenFunction::EmitMaterializeTemporaryExpr(
     }
   }
 
-  // Create and initialize the reference temporary.
-  llvm::Value *Object = createReferenceTemporary(*this, M, E);
+  // Create and initialize the reference temporary and get the temporary size
+  llvm::Value *ObjectSize;
+  llvm::Value *Object = createReferenceTemporary(*this, M, E, ObjectSize);
+
   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.
@@ -363,7 +378,8 @@ LValue CodeGenFunction::EmitMaterializeTemporaryExpr(
   } else {
     EmitAnyExprToMem(E, Object, Qualifiers(), /*IsInit*/true);
   }
-  pushTemporaryCleanup(*this, M, E, Object);
+
+  pushTemporaryCleanup(*this, M, E, Object, ObjectSize);
 
   // Perform derived-to-base casts and/or field accesses, to get from the
   // temporary object we created (and, potentially, for which we extended
-- 
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