Re: [PATCH v2] lib/mpi: Eliminate unused umul_ppmm definitions for MIPS

From: Nick Desaulniers
Date: Mon Aug 12 2019 - 15:38:02 EST


On Mon, Aug 12, 2019 at 12:36 PM Nathan Chancellor
<natechancellor@xxxxxxxxx> wrote:
>
> Clang errors out when building this macro:
>
> lib/mpi/generic_mpih-mul1.c:37:24: error: invalid use of a cast in a
> inline asm context requiring an l-value: remove the cast or build with
> -fheinous-gnu-extensions
> umul_ppmm(prod_high, prod_low, s1_ptr[j], s2_limb);
> ~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> lib/mpi/longlong.h:652:20: note: expanded from macro 'umul_ppmm'
> : "=l" ((USItype)(w0)), \
> ~~~~~~~~~~^~~
> lib/mpi/generic_mpih-mul1.c:37:3: error: invalid output constraint '=h'
> in asm
> umul_ppmm(prod_high, prod_low, s1_ptr[j], s2_limb);
> ^
> lib/mpi/longlong.h:653:7: note: expanded from macro 'umul_ppmm'
> "=h" ((USItype)(w1)) \
> ^
> 2 errors generated.
>
> The C version that is used for GCC 4.4 and up works well with clang;
> however, it is not currently being used because Clang masks itself
> as GCC 4.2.1 for compatibility reasons. As Nick points out, we require
> GCC 4.6 and newer in the kernel so we can eliminate all of the
> versioning checks and just use the C version of umul_ppmm for all
> supported compilers.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/605
> Suggested-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
> Signed-off-by: Nathan Chancellor <natechancellor@xxxxxxxxx>

LGTM thanks Nathan.
Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>

> ---
>
> This supersedes the following two patches:
>
> https://lore.kernel.org/lkml/20190812033120.43013-4-natechancellor@xxxxxxxxx/
>
> https://lore.kernel.org/lkml/20190812033120.43013-5-natechancellor@xxxxxxxxx/
>
> I labelled this as a v2 so those don't get applied.
>
> lib/mpi/longlong.h | 36 +-----------------------------------
> 1 file changed, 1 insertion(+), 35 deletions(-)
>
> diff --git a/lib/mpi/longlong.h b/lib/mpi/longlong.h
> index 3bb6260d8f42..2dceaca27489 100644
> --- a/lib/mpi/longlong.h
> +++ b/lib/mpi/longlong.h
> @@ -639,30 +639,12 @@ do { \
> ************** MIPS *****************
> ***************************************/
> #if defined(__mips__) && W_TYPE_SIZE == 32
> -#if (__GNUC__ >= 5) || (__GNUC__ >= 4 && __GNUC_MINOR__ >= 4)
> #define umul_ppmm(w1, w0, u, v) \
> do { \
> UDItype __ll = (UDItype)(u) * (v); \
> w1 = __ll >> 32; \
> w0 = __ll; \
> } while (0)
> -#elif __GNUC__ > 2 || __GNUC_MINOR__ >= 7
> -#define umul_ppmm(w1, w0, u, v) \
> - __asm__ ("multu %2,%3" \
> - : "=l" ((USItype)(w0)), \
> - "=h" ((USItype)(w1)) \
> - : "d" ((USItype)(u)), \
> - "d" ((USItype)(v)))
> -#else
> -#define umul_ppmm(w1, w0, u, v) \
> - __asm__ ("multu %2,%3\n" \
> - "mflo %0\n" \
> - "mfhi %1" \
> - : "=d" ((USItype)(w0)), \
> - "=d" ((USItype)(w1)) \
> - : "d" ((USItype)(u)), \
> - "d" ((USItype)(v)))
> -#endif
> #define UMUL_TIME 10
> #define UDIV_TIME 100
> #endif /* __mips__ */
> @@ -687,7 +669,7 @@ do { \
> : "d" ((UDItype)(u)), \
> "d" ((UDItype)(v))); \
> } while (0)
> -#elif (__GNUC__ >= 5) || (__GNUC__ >= 4 && __GNUC_MINOR__ >= 4)
> +#else
> #define umul_ppmm(w1, w0, u, v) \
> do { \
> typedef unsigned int __ll_UTItype __attribute__((mode(TI))); \
> @@ -695,22 +677,6 @@ do { \
> w1 = __ll >> 64; \
> w0 = __ll; \
> } while (0)
> -#elif __GNUC__ > 2 || __GNUC_MINOR__ >= 7
> -#define umul_ppmm(w1, w0, u, v) \
> - __asm__ ("dmultu %2,%3" \
> - : "=l" ((UDItype)(w0)), \
> - "=h" ((UDItype)(w1)) \
> - : "d" ((UDItype)(u)), \
> - "d" ((UDItype)(v)))
> -#else
> -#define umul_ppmm(w1, w0, u, v) \
> - __asm__ ("dmultu %2,%3\n" \
> - "mflo %0\n" \
> - "mfhi %1" \
> - : "=d" ((UDItype)(w0)), \
> - "=d" ((UDItype)(w1)) \
> - : "d" ((UDItype)(u)), \
> - "d" ((UDItype)(v)))
> #endif
> #define UMUL_TIME 20
> #define UDIV_TIME 140
> --
> 2.23.0.rc2
>


--
Thanks,
~Nick Desaulniers