[rfc] fix umul_ppmm() in our libgcc

[Warner Losh]

> On Jun 13, 2015, at 4:41 PM, Adrian Chadd <adrian at freebsd.org> wrote:
> 
> Hi,
> 
> our libgcc in -base is very .. old. It chokes when compiling for
> mips32. This patch seems to do the right thing.
> 
> Does anyone have any positive/negative feedback?

What code does it generate?

Something doesn’t look quite right, but I can’t quite put my finger on it.

Warner

> Thanks,
> 
> 
> -adrian
> 
> 
> Index: contrib/gcc/longlong.h
> ===================================================================
> --- contrib/gcc/longlong.h      (revision 284090)
> +++ contrib/gcc/longlong.h      (working copy)
> @@ -584,11 +584,11 @@
> 
> #if defined (__mips__) && W_TYPE_SIZE == 32
> #define umul_ppmm(w1, w0, u, v) \
> -  __asm__ ("multu %2,%3"                                               \
> -          : "=l" ((USItype) (w0)),                                     \
> -            "=h" ((USItype) (w1))                                      \
> -          : "d" ((USItype) (u)),                                       \
> -            "d" ((USItype) (v)))
> +       do {                                                            \
> +        UDItype __ll = (UDItype)(u) * (v);                             \
> +        w1 = __ll >> 32;                                               \
> +        w0 = __ll;                                                     \
> +       } while (0)
> #define UMUL_TIME 10
> #define UDIV_TIME 100
> #endif /* __mips__ */
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