svn commit: r211505 - head/contrib/gcc

Dimitry Andric dimitry at
Sat Aug 21 13:59:41 UTC 2010

On 2010-08-20 22:36, Bruce Evans wrote:
> On Fri, 20 Aug 2010, Dimitry Andric wrote:
>> But will the casts not potentially hide problems, if you pass the wrong
>> types to those macros?  Maybe it is better if the compiler complains
>> that some argument is of an incompatible type, than just forcing it to
>> cast?
> This is unclear.  All integer types are compatible to some extent.
> Upcasting them always works and downcasting them works iff the value
> is not changed.

I meant this in the context of this llvm PR, about matching inline asm
input constraints with output constraints of an incompatible type:

Clang is currently somewhat pickier about the arguments to inline asm,
which we also noticed in OpenSSL code, where a rotate-left macro is
defined (for i386 and amd64) as:

#   define ROTATE(a,n)	({ register unsigned int ret;	\
				  asm (			\
				  "roll %1,%0"		\
				  : "=r"(ret)		\
				  : "I"(n), "0"(a)	\
				  : "cc");		\
			     ret;			\

On amd64, it was being called with the 'a' argument being of unsigned
long type.  Clang complained:

error: unsupported inline asm: input with type 'unsigned long' matching
output with type 'unsigned int'
	  R0(A,B,C,D,X( 0), 3,0); HOST_c2l(data,l); X( 2)=l;

In this case, the OpenSSL developers chose to explicitly cast 'a' to
'unsigned int' (see <>).

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