intel/fs: Constant fold SHL

intel/fs: Constant fold SHL

This is a modified version of a commit originally in !7698. This version
add the changes to brw_fs_copy_propagation. If the address passed to
fs_visitor::swizzle_nir_scratch_addr is a constant, that function will
generate SHL with two constant sources.

DG2 uses a different path to generate those addresses, so the constant
folding can't occur there yet. That will be addressed in the next
commit.

What follows is the commit change history from that older MR.

v2: Previously this commit was after `intel/fs: Combine constants for
integer instructions too`.  However, this commit can create invalid
instructions that are only cleaned up by `intel/fs: Combine constants
for integer instructions too`.  That would potentially affect the
shader-db results of each commit, but I did not collect new data for
the reordering.

v3: Fix masking for W/UW and for Q/UQ types. Add an assertion for
!saturate. Both suggested by Ken. Also add an assertion that B/UB types
don't matically come back.

v4: Fix sources count. See also ed3c2f73dbb ("intel/fs: fixup sources
number from opt_algebraic").

v5: Fix typo in comment added in v3. Noticed by Marcin. Fix a typo in a
comment added when pulling this commit out of !7698. Noticed by Ken.

shader-db results:

DG2
No changes.

Tiger Lake, Ice Lake, and Skylake had similar results (Ice Lake shown)
total instructions in shared programs: 20655696 -> 20651648 (-0.02%)
instructions in affected programs: 23125 -> 19077 (-17.50%)
helped: 7 / HURT: 0

total cycles in shared programs: 858436639 -> 858407749 (<.01%)
cycles in affected programs: 8990532 -> 8961642 (-0.32%)
helped: 7 / HURT: 0

Broadwell and Haswell had similar results. (Broadwell shown)
total instructions in shared programs: 18500780 -> 18496630 (-0.02%)
instructions in affected programs: 24715 -> 20565 (-16.79%)
helped: 7 / HURT: 0

total cycles in shared programs: 946100660 -> 946087688 (<.01%)
cycles in affected programs: 5838252 -> 5825280 (-0.22%)
helped: 7 / HURT: 0

total spills in shared programs: 17588 -> 17572 (-0.09%)
spills in affected programs: 1206 -> 1190 (-1.33%)
helped: 2 / HURT: 0

total fills in shared programs: 25192 -> 25156 (-0.14%)
fills in affected programs: 156 -> 120 (-23.08%)
helped: 2 / HURT: 0

No shader-db changes on any older Intel platforms.

fossil-db results:

DG2
Totals:
Instrs: 197780415 -> 197780372 (-0.00%); split: -0.00%, +0.00%
Cycles: 14066412266 -> 14066410782 (-0.00%); split: -0.00%, +0.00%

Totals from 16 (0.00% of 668055) affected shaders:
Instrs: 16420 -> 16377 (-0.26%); split: -0.43%, +0.17%
Cycles: 220133 -> 218649 (-0.67%); split: -0.69%, +0.01%

Tiger Lake, Ice Lake and Skylake had similar results. (Ice Lake shown)
Totals:
Instrs: 153425977 -> 153423678 (-0.00%)
Cycles: 14747928947 -> 14747929547 (+0.00%); split: -0.00%, +0.00%
Subgroup size: 8535968 -> 8535976 (+0.00%)
Send messages: 7697606 -> 7697607 (+0.00%)
Scratch Memory Size: 4380672 -> 4381696 (+0.02%)

Totals from 6 (0.00% of 662749) affected shaders:
Instrs: 13893 -> 11594 (-16.55%)
Cycles: 5386074 -> 5386674 (+0.01%); split: -0.42%, +0.43%
Subgroup size: 80 -> 88 (+10.00%)
Send messages: 675 -> 676 (+0.15%)
Scratch Memory Size: 91136 -> 92160 (+1.12%)

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/23884>