[Sparc] efficient pattern for UINT_TO_FP conversion

Summary:
        while investigating performance degradation of imagick benchmark
        there were found inefficient pattern for UINT_TO_FP conversion.
        That pattern causes RAW hazard in assembly code. Specifically,
        uitofp IR operator results in poor assembler :

        st          %i0, [%fp - 952]
        ldd         [%fp - 952], %f0

        it stores 32-bit integer register into memory location and then
        loads 64-bit floating point data from that location.
        That is exactly RAW hazard case. To optimize that case it is
        possible to use SPISD::ITOF and SPISD::XTOF for conversion from
        integer to floating point data type and to use ISD::BITCAST to
        copy from integer register into floating point register.
        The fix is to write custom UINT_TO_FP pattern using SPISD::ITOF,
        SPISD::XTOF, ISD::BITCAST.

Patch by Alexey Lapshin

Reviewers: fedor.sergeev, jyknight, dcederman, lero_chris

Reviewed By: jyknight

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D36875

llvm-svn: 318704