Re: [PATCH] powerpc: Restrict xssqrtqp operands to Vector Registers (Altivec/VMX)

["Tulio Magno Quites Machado Filho" <tuliom at linux dot vnet dot ibm dot com>]

"Gabriel F. T. Gomes" <gftg@linux.vnet.ibm.com> writes:

> POWER ISA 3.0 introduces the xssqrtqp instructions, which expects
> operands to be in Vector Registers (Altivec/VMX), even though this
> instruction belongs to the Vector-Scalar Instruction Set.
>
> In GCC's Extended Assembly for POWER, the 'wq' register constraint is
> provided for use with IEEE 754 128-bit floating-point values.  However,
> this constrain does not limit the register allocation to Vector

s/constrain/constraint/

> Registers (Altivec/VMX) and could assign a Vector-Scalar Register (VSX)
> to the operands of the instruction.
>
> This patch changes the register constraint used in sqrtf128 from 'wq' to
> 'v', in order to request a Vector Register (Altivec/VMX) for use with
> the xssqrtqp instruction.
>
> Tested for powerpc64le and --with-cpu=power9.
>
> 	* sysdeps/powerpc/fpu/math_private.h (__ieee754_sqrtf128): Since
> 	xssqrtqp requires operands to be in Vector Registers
> 	(Altivec/VMX), replace the register constraint 'wq' with 'v'.
> 	* sysdeps/powerpc/powerpc64le/power9/fpu/e_sqrtf128.c
> 	(__ieee754_sqrtf128): Likewise.

Looks good to me, but as it affects glibc 2.26, I think we need a bug report
and a bugzilla number in the commit message.

Thanks!

-- 
Tulio Magno