intel/compiler: fix cmod propagation optimisations

intel/compiler: fix cmod propagation optimisations

Knowing following:
 - CMP writes to flag register the result of
   applying cmod to the `src0 - src1`.
   After that it stores the same value to dst.
   Other instructions first store their result to
   dst, and then store cmod(dst) to the flag
   register.
 - inst is either CMP or MOV
 - inst->dst is null
 - inst->src[0] overlaps with scan_inst->dst
 - inst->src[1] is zero
 - scan_inst wrote to a flag register

There can be three possible paths:

 - scan_inst is CMP:

   Considering that src0 is either 0x0 (false),
   or 0xffffffff (true), and src1 is 0x0:

   - If inst's cmod is NZ, we can always remove
     scan_inst: NZ is invariant for false and true. This
     holds even if src0 is NaN: .nz is the only cmod,
     that returns true for NaN.

   - .g is invariant if src0 has a UD type

   - .l is invariant if src0 has a D type

 - scan_inst and inst have the same cmod:

   If scan_inst is anything than CMP, it already
   wrote the appropriate value to the flag register.

 - else:

   We can change cmod of scan_inst to that of inst,
   and remove inst. It is valid as long as we make
   sure that no instruction uses the flag register
   between scan_inst and inst.

Nine new cmod_propagation unit tests:
 - cmp_cmpnz
 - cmp_cmpg
 - plnnz_cmpnz
 - plnnz_cmpz (*)
 - plnnz_sel_cmpz
 - cmp_cmpg_D
 - cmp_cmpg_UD (*)
 - cmp_cmpl_D (*)
 - cmp_cmpl_UD

(*) this would fail without changes to brw_fs_cmod_propagation.

This fixes optimisation that used to be illegal (see issue #2154)

= Before =
 0: linterp.z.f0.0(8) vgrf0:F, g2:F, attr0<0>:F
 1: cmp.nz.f0.0(8) null:F, vgrf0:F, 0f
= After =
 0: linterp.z.f0.0(8) vgrf0:F, g2:F, attr0<0>:F

Now it is optimised as such (note change of cmod in line 0):

= Before =
 0: linterp.z.f0.0(8) vgrf0:F, g2:F, attr0<0>:F
 1: cmp.nz.f0.0(8) null:F, vgrf0:F, 0f
= After =
 0: linterp.nz.f0.0(8) vgrf0:F, g2:F, attr0<0>:F

No shaderdb changes

Closes: https://gitlab.freedesktop.org/mesa/mesa/issues/2154
Signed-off-by: Yevhenii Kolesnikov <yevhenii.kolesnikov@globallogic.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/3348>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/3348>