rjmccall added inline comments.
================
Comment at: lib/CodeGen/CGExprConstant.cpp:1340
+ return C;
+ return getNullPtr(PT, DestType);
}
----------------
yaxunl wrote:
> efriedma wrote:
> > yaxunl wrote:
> > > yaxunl wrote:
> > > > rjmccall wrote:
> > > > > efriedma wrote:
> > > > > > Consider code like the following:
> > > > > >
> > > > > > int x = 0;
> > > > > > auto y1 = (__specialaddrspace int*)0;
> > > > > > auto y2 = (__specialaddrspace int*)((void)0, 0);
> > > > > > auto y3 = (__specialaddrspace int*)x;
> > > > > >
> > > > > > How do you expect these three cases to behave? (The first case
> > > > > > involves a C null pointer constant, the second and third cases are
> > > > > > different ways of writing a general int->ptr conversion.)
> > > > > Yeah, I think you probably need to fix APValue to be unambiguous
> > > > > about whether the value is a formal null pointer (CK_NullToPointer)
> > > > > or just a cast of an integer (CK_IntegralToPointer). It looks like
> > > > > PointerExprEvaluator will generate the exact same value for both.
> > > > It seems the current implementation generates the correct IR.
> > > >
> > > > I tried the following sample and I saw correct IR generated.
> > > >
> > > >
> > > > ```
> > > > private int* test_cast_0_to_ptr(void) {
> > > > return (private int*)0;
> > > > }
> > > >
> > > > private int* test_cast_int_to_ptr1(void) {
> > > > return (private int*)((void)0, 0);
> > > > }
> > > >
> > > > private int* test_cast_int_to_ptr2(void) {
> > > > int x = 0;
> > > > return (private int*)x;
> > > > }
> > > >
> > > > ```
> > > >
> > > > The dumped AST is
> > > >
> > > >
> > > > ```
> > > > |-FunctionDecl 0x95fdc88 <ptr.cl:3:1, line:5:1> line:3:14
> > > > test_cast_0_to_ptr 'int *(void)'
> > > > | `-CompoundStmt 0x95fdde8 <col:39, line:5:1>
> > > > | `-ReturnStmt 0x95fddd0 <line:4:3, col:24>
> > > > | `-CStyleCastExpr 0x95fdda8 <col:10, col:24> 'int *'
> > > > <NullToPointer>
> > > > | `-IntegerLiteral 0x95fdd70 <col:24> 'int' 0
> > > > |-FunctionDecl 0x95fdea0 <line:13:1, line:15:1> line:13:14
> > > > test_cast_int_to_ptr1 'int *(void)'
> > > > | `-CompoundStmt 0x95fe098 <col:42, line:15:1>
> > > > | `-ReturnStmt 0x95fe080 <line:14:3, col:35>
> > > > | `-CStyleCastExpr 0x95fe058 <col:10, col:35> 'int *'
> > > > <IntegralToPointer>
> > > > | `-ParenExpr 0x95fe038 <col:24, col:35> 'int'
> > > > | `-BinaryOperator 0x95fe010 <col:25, col:34> 'int' ','
> > > > | |-CStyleCastExpr 0x95fdf78 <col:25, col:31> 'void' <ToVoid>
> > > > | | `-IntegerLiteral 0x95fdf48 <col:31> 'int' 0
> > > > | `-IntegerLiteral 0x95fdfa0 <col:34> 'int' 0
> > > > `-FunctionDecl 0x95fe150 <line:19:1, line:22:1> line:19:14
> > > > test_cast_int_to_ptr2 'int *(void)'
> > > > `-CompoundStmt 0x9620130 <col:42, line:22:1>
> > > > |-DeclStmt 0x9620080 <line:20:3, col:12>
> > > > | `-VarDecl 0x95fe210 <col:3, col:11> col:7 used x 'int' cinit
> > > > | `-IntegerLiteral 0x9620060 <col:11> 'int' 0
> > > > `-ReturnStmt 0x9620118 <line:21:3, col:24>
> > > > `-CStyleCastExpr 0x96200f0 <col:10, col:24> 'int *'
> > > > <IntegralToPointer>
> > > > ```
> > > >
> > > > Since only CK_NullToPointer is translated to null pointer through
> > > > getNullPtr, CK_IntegralToPointer will result in either zero-valued
> > > > pointer or inttoptr, the generated IR is correct.
> > > Basically in the second and third case the destination type is not
> > > pointer, so they do not need to be emitted as null pointer. If a literal
> > > 0 is casted to a pointer type, then it should be emitted as a null
> > > pointer.
> > What happens in the following case?
> >
> > static private int* x = (private int*)((void)0, 0);
> You are right. This needs to be fixed.
Another straightforward test case would be reinterpret_cast<private void*>(0),
or (private void*) (1-1) in C++11.
https://reviews.llvm.org/D26196
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