On Tue, Jul 24, 2012 at 2:24 PM, Rafael Espíndola
<[email protected]> wrote:
> I found that clang's implementation of regparm doesn't match gcc's
> when the argument is a struct. Clang just skips the struct, gcc splits
> it in 32 bit chunks that are passed in registers. Not too different
> from the x86-64 abi.
>
> In a bit more detail, it looks like gcc does the following:
>
> * Arguments of type float, double, {float} and {double} are classified as
> Float, and every other argument type is classified as Integer.
> * Float arguments are passed on the stack and don't consume registers.
> * If an integer argument fits completely in the remaining registers, it is
> passed in registers, otherwise it goes to the stack.
> * Integer arguments consume registers even if they don't fit, so once an
> argument goes to the stack every other argument goes to the stack.
> * A struct return is still done indirectly, but the pointer is passed
> as the first argument in registers.
>
> This patch implements this. Note that it depends on the patch I just
> posted to the llvm list.
+ if (const RecordType *RT = Ty->getAs<RecordType>()) {
+ const RecordDecl *RD = RT->getDecl();
+ RecordDecl::field_iterator I = RD->field_begin();
+ RecordDecl::field_iterator E = RD->field_end();
+ if (I == E)
+ return Integer;
+ QualType FieldType = I->getType();
+ ++I;
+ if (I != E)
+ return Integer;
+ if (const BuiltinType *BT = FieldType->getAs<BuiltinType>()) {
+ BuiltinType::Kind K = BT->getKind();
+ if (K == BuiltinType::Float || K == BuiltinType::Double)
+ return Float;
+ }
+ }
I think you want isSingleElementStruct() here.
Have you tried randomized ABI testing? (Either the one in the gcc
testsuite or the one in clang/utils/ABITest.)
-Eli
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