[cfe-commits] r130717 - in /cfe/trunk: lib/CodeGen/CGCall.cpp lib/CodeGen/CGCall.h test/CodeGen/byval-memcpy-elim.c

[Douglas Gregor]

On May 2, 2011, at 1:24 PM, Eli Friedman wrote:

> Author: efriedma
> Date: Mon May  2 15:24:29 2011
> New Revision: 130717
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=130717&view=rev
> Log:
> Skip extra copy from aggregate where it isn't necessary; rdar://problem/8139919 .  This shouldn't make much of a difference at -O3, but should substantially reduce the number of generated memcpy's at -O0.

This is causing us to get zeroed struct returns in some cases (<rdar://problem/9402621>). Here's a failing example:

#import <AppKit/AppKit.h>

@interface MyObject : NSObject
+ (NSRect)doubleRect:(NSRect)rect;
@end

@implementation MyObject

+ (NSRect)doubleRect:(NSRect)rect
{
  NSLog(@"input rect is: %@", NSStringFromRect(rect));
  return NSMakeRect(rect.origin.x * 2, rect.origin.y * 2, rect.size.width * 2, rect.size.height * 2);
}

@end

int main() {
  NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];

  NSRect rect = NSMakeRect(100, 200, 300, 400);
  NSLog(@"rect is: %@", NSStringFromRect(rect));

  rect = [MyObject doubleRect:rect];
  NSLog(@"rect is now: %@", NSStringFromRect(rect));

  [pool drain];
}

I've reverted this change in r131057.

	- Doug

> 
> Added:
>    cfe/trunk/test/CodeGen/byval-memcpy-elim.c
> Modified:
>    cfe/trunk/lib/CodeGen/CGCall.cpp
>    cfe/trunk/lib/CodeGen/CGCall.h
> 
> Modified: cfe/trunk/lib/CodeGen/CGCall.cpp
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/CGCall.cpp?rev=130717&r1=130716&r2=130717&view=diff
> ==============================================================================
> --- cfe/trunk/lib/CodeGen/CGCall.cpp (original)
> +++ cfe/trunk/lib/CodeGen/CGCall.cpp Mon May  2 15:24:29 2011
> @@ -1166,6 +1166,15 @@
>     return args.add(EmitReferenceBindingToExpr(E, /*InitializedDecl=*/0),
>                     type);
> 
> +  if (hasAggregateLLVMType(type) && isa<ImplicitCastExpr>(E) &&
> +      cast<CastExpr>(E)->getCastKind() == CK_LValueToRValue) {
> +    LValue L = EmitLValue(cast<CastExpr>(E)->getSubExpr());
> +    assert(L.isSimple());
> +    args.add(RValue::getAggregate(L.getAddress(), L.isVolatileQualified()),
> +             type, /*NeedsCopy*/true);
> +    return;
> +  }
> +
>   args.add(EmitAnyExprToTemp(E), type);
> }
> 
> @@ -1231,6 +1240,10 @@
>                             Alignment, I->Ty);
>         else
>           StoreComplexToAddr(RV.getComplexVal(), Args.back(), false);
> +      } else if (I->NeedsCopy && !ArgInfo.getIndirectByVal()) {
> +        Args.push_back(CreateMemTemp(I->Ty));
> +        EmitAggregateCopy(Args.back(), RV.getAggregateAddr(), I->Ty,
> +                          RV.isVolatileQualified());
>       } else {
>         Args.push_back(RV.getAggregateAddr());
>       }
> 
> Modified: cfe/trunk/lib/CodeGen/CGCall.h
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/CGCall.h?rev=130717&r1=130716&r2=130717&view=diff
> ==============================================================================
> --- cfe/trunk/lib/CodeGen/CGCall.h (original)
> +++ cfe/trunk/lib/CodeGen/CGCall.h Mon May  2 15:24:29 2011
> @@ -47,8 +47,9 @@
>   struct CallArg {
>     RValue RV;
>     QualType Ty;
> -    CallArg(RValue rv, QualType ty)
> -    : RV(rv), Ty(ty)
> +    bool NeedsCopy;
> +    CallArg(RValue rv, QualType ty, bool needscopy)
> +    : RV(rv), Ty(ty), NeedsCopy(needscopy)
>     { }
>   };
> 
> @@ -57,8 +58,8 @@
>   class CallArgList :
>     public llvm::SmallVector<CallArg, 16> {
>   public:
> -    void add(RValue rvalue, QualType type) {
> -      push_back(CallArg(rvalue, type));
> +    void add(RValue rvalue, QualType type, bool needscopy = false) {
> +      push_back(CallArg(rvalue, type, needscopy));
>     }
>   };
> 
> 
> Added: cfe/trunk/test/CodeGen/byval-memcpy-elim.c
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGen/byval-memcpy-elim.c?rev=130717&view=auto
> ==============================================================================
> --- cfe/trunk/test/CodeGen/byval-memcpy-elim.c (added)
> +++ cfe/trunk/test/CodeGen/byval-memcpy-elim.c Mon May  2 15:24:29 2011
> @@ -0,0 +1,20 @@
> +// RUN: %clang_cc1 -emit-llvm -triple x86_64-apple-darwin10 < %s | FileCheck %s
> +
> +struct Test1S {
> + long NumDecls;
> + long X;
> + long Y;
> +};
> +struct Test2S {
> + long NumDecls;
> + long X;
> +};
> +
> +// Make sure we don't generate extra memcpy for lvalues
> +void test1a(struct Test1S, struct Test2S);
> +// CHECK: define void @test1(
> +// CHECK-NOT: memcpy
> +// CHECK: call void @test1a
> +void test1(struct Test1S *A, struct Test2S *B) {
> +  test1a(*A, *B);
> +}
> 
> 
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