No memcpy for copy ctor with -fsanitize-address-field-padding=1

[kcc]

Summary

When -fsanitize-address-field-padding=1 is present
don't emit memcpy for copy constructor.
Thanks Nico for the extra test case.

[kcc]

+rsmith

[rsmith]

LGTM

[thakis]

Sorry about the slow review.

Rather than adding all these checks before calling EmitAggregateCopy(), is it maybe possible to do this check in EmitAggregateCopy() itself? Else there will always be cases that you miss. For example:

$ cat foo.cc
struct ClassWithTrivialCopy {
  ClassWithTrivialCopy();
  ~ClassWithTrivialCopy();
  void *a;
 private:
  void *c;
};

struct NontrivialCopy { 
  NontrivialCopy(const NontrivialCopy&); 
};

struct pair {
  NontrivialCopy nc;
  ClassWithTrivialCopy second[4];
  pair(const pair&) = default;
};

void MakeTrivialCopy( const pair &p) {
  pair p2(p);
}
$ bin/clang -c foo.cc -std=c++11 -fsanitize=address -fsanitize-address-field-padding=1  -emit-llvm -S -o - | grep memcpy
  %68 = call i8* @__asan_memcpy(i8* %66, i8* %67, i64 128)
declare void @llvm.memcpy.p0i8.p0i8.i64(i8* nocapture, i8* nocapture readonly, i64, i32, i1) #4
declare i8* @__asan_memcpy(i8*, i8*, i64)

lib/CodeGen/CGClass.cpp

 }
 
 void CodeGenFunction::EmitCXXConstructorCall(const CXXConstructorDecl *D,
                                              CXXCtorType Type,
                                              bool ForVirtualBase,
                                              bool Delegating, llvm::Value *This,
                                              const CXXConstructExpr *E) {
   // If this is a trivial constructor, just emit what's needed.
-  if (D->isTrivial()) {
+  if (D->isTrivial() && !D->getParent()->mayInsertExtraPadding()) {
     if (E->getNumArgs() == 0) {
       // Trivial default constructor, no codegen required.
       assert(D->isDefaultConstructor() &&
              "trivial 0-arg ctor not a default ctor");
       return;
     }
 
     assert(E->getNumArgs() == 1 && "unexpected argcount for trivial ctor");
const CGFunctionInfo &Info =
       CGM.getTypes().arrangeCXXConstructorCall(Args, D, Type, ExtraArgs);
   EmitCall(Info, Callee, ReturnValueSlot(), Args, D);
 }
 
 void
 CodeGenFunction::EmitSynthesizedCXXCopyCtorCall(const CXXConstructorDecl *D,
                                         llvm::Value *This, llvm::Value *Src,
                                         const CXXConstructExpr *E) {
-  if (D->isTrivial()) {
+  if (D->isTrivial() &&
+      !D->getParent()->mayInsertExtraPadding()) {
     assert(E->getNumArgs() == 1 && "unexpected argcount for trivial ctor");
     assert(D->isCopyOrMoveConstructor() &&
            "trivial 1-arg ctor not a copy/move ctor");
     EmitAggregateCopy(This, Src, E->arg_begin()->getType());
     return;
   }
   llvm::Value *Callee = CGM.getAddrOfCXXStructor(D, StructorType::Complete);
   assert(D->isInstance() &&

test/CodeGen/sanitize-address-field-padding.cpp

struct ClassWithTrivialCopy {
   ~ClassWithTrivialCopy();
   void *a;
  private:
   void *c;
 };
 
 void MakeTrivialCopy(ClassWithTrivialCopy *s1, ClassWithTrivialCopy *s2) {
   *s1 = *s2;
+  ClassWithTrivialCopy s3(*s2);
 }
 
 // CHECK-LABEL: define void @_Z15MakeTrivialCopyP20ClassWithTrivialCopyS0_
 // CHECK-NOT: memcpy
 // CHECK: ret void