From 82e1af20cb6393345bf53259465d63743d9b60db Mon Sep 17 00:00:00 2001
From: Douglas Gregor <dgregor@apple.com>
Date: Fri, 1 Jul 2011 21:08:19 +0000
Subject: [PATCH] Don't zero-initialize default-initialized local variables
 that have trivial default constructors. This generated-code regression was
 caused by r131796, which had simplified the handling of default
 initialization in Sema. Fixes <rdar://problem/9694300>.

llvm-svn: 134260
---
 clang/lib/CodeGen/CGDecl.cpp               | 19 ++++++++++++++++++-
 clang/test/CodeGenCXX/constructor-init.cpp | 16 ++++++++++++++++
 2 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/clang/lib/CodeGen/CGDecl.cpp b/clang/lib/CodeGen/CGDecl.cpp
index d508ff7390bb..95294bf8e583 100644
--- a/clang/lib/CodeGen/CGDecl.cpp
+++ b/clang/lib/CodeGen/CGDecl.cpp
@@ -873,6 +873,21 @@ static bool isCapturedBy(const VarDecl &var, const Expr *e) {
   return false;
 }
 
+/// \brief Determine whether the given initializer is trivial in the sense
+/// that it requires no code to be generated.
+static bool isTrivialInitializer(const Expr *Init) {
+  if (!Init)
+    return true;
+  
+  if (const CXXConstructExpr *Construct = dyn_cast<CXXConstructExpr>(Init))
+    if (CXXConstructorDecl *Constructor = Construct->getConstructor())
+      if (Constructor->isTrivial() &&
+          Constructor->isDefaultConstructor() &&
+          !Construct->requiresZeroInitialization())
+        return true;
+      
+  return false;
+}
 void CodeGenFunction::EmitAutoVarInit(const AutoVarEmission &emission) {
   assert(emission.Variable && "emission was not valid!");
 
@@ -896,7 +911,9 @@ void CodeGenFunction::EmitAutoVarInit(const AutoVarEmission &emission) {
   if (emission.IsByRef)
     emitByrefStructureInit(emission);
 
-  if (!Init) return;
+  if (isTrivialInitializer(Init))
+    return;
+  
 
   CharUnits alignment = emission.Alignment;
 
diff --git a/clang/test/CodeGenCXX/constructor-init.cpp b/clang/test/CodeGenCXX/constructor-init.cpp
index 47e3b7b0bb90..f439083c0778 100644
--- a/clang/test/CodeGenCXX/constructor-init.cpp
+++ b/clang/test/CodeGenCXX/constructor-init.cpp
@@ -133,3 +133,19 @@ template<typename T>
 X<T>::X(const X &other) : start(0), end(0) { }
 
 X<int> get_X(X<int> x) { return x; }
+
+namespace rdar9694300 {
+  struct X {
+    int x;
+  };
+
+  // CHECK: define void @_ZN11rdar96943001fEv
+  void f() {
+    // CHECK: alloca
+    X x;
+    // CHECK-NEXT: [[I:%.*]] = alloca i32
+    // CHECK-NEXT: store i32 17, i32* [[I]]
+    int i = 17;
+    // CHECK-NEXT: ret void
+  }
+}