Felipe Magno de Almeida e3fdc3aa81 [RISCV] Allow hoisting VXRM writes out of loops speculatively (#110044) ...

Change the intersect for the anticipated algorithm to ignore unknown
when anticipating. This effectively allows VXRM writes speculatively
because it could do a VXRM write even when there's branches where VXRM
is unneeded.

The importance of this change is because VXRM writes causes pipeline
flushes in some micro-architectures and so it makes sense to allow more
aggressive hoisting even if it causes some degradation for the slow
path.

An example is this code:
```
typedef unsigned char uint8_t;
__attribute__ ((noipa))
void foo (uint8_t *dst,  int i_dst_stride,
           uint8_t *src1, int i_src1_stride,
           uint8_t *src2, int i_src2_stride,
           int i_width, int i_height )
{
   for( int y = 0; y < i_height; y++ )
     {
       for( int x = 0; x < i_width; x++ )
         dst[x] = ( src1[x] + src2[x] + 1 ) >> 1;
       dst  += i_dst_stride;
       src1 += i_src1_stride;
       src2 += i_src2_stride;
     }
}
```
With this patch, the code above generates a hoisting VXRM writes out of
the outer loop.

2024-11-27 13:31:39 -08:00

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