When I implemented opt_if_loop_last_continue() I had restricted
this pass from moving other if-statements inside the branch opposite
the continue. At the time it was causing extra regisiter pressure
in some shaders, however that no longer seems to be an issue.

Samuel Pitoiset noticed that making this pass more aggressive
significantly improved the performance of Doom on RADV. Below are
the statistics he gathered.

28717 shaders in 14931 tests
Totals:
SGPRS: 1267317 -> 1267549 (0.02 %)
VGPRS: 896876 -> 895920 (-0.11 %)
Spilled SGPRs: 24701 -> 26367 (6.74 %)
Code Size: 48379452 -> 48507880 (0.27 %) bytes
Max Waves: 241159 -> 241190 (0.01 %)

Totals from affected shaders:
SGPRS: 23584 -> 23816 (0.98 %)
VGPRS: 25908 -> 24952 (-3.69 %)
Spilled SGPRs: 503 -> 2169 (331.21 %)
Code Size: 2471392 -> 2599820 (5.20 %) bytes
Max Waves: 586 -> 617 (5.29 %)

The codesize increases is related to Wolfenstein II.

This gives +10% FPS with Doom on my Vega56.

Rhys Perry also benchmarked Doom on his VEGA64:

Before: 72.53 FPS
After:  80.77 FPS

shader-db results i965 (SKL):

total instructions in shared programs: 15029076 -> 15029877 (<.01%)
instructions in affected programs: 493251 -> 494052 (0.16%)
helped: 3
HURT: 374

total cycles in shared programs: 263387688 -> 263401720 (<.01%)
cycles in affected programs: 30658226 -> 30672258 (0.05%)
helped: 3
HURT: 374

total spills in shared programs: 9691 -> 9748 (0.59%)
spills in affected programs: 88 -> 145 (64.77%)
helped: 0
HURT: 4

total fills in shared programs: 22076 -> 22133 (0.26%)
fills in affected programs: 128 -> 185 (44.53%)
helped: 0
HURT: 4

LOST:   0
GAINED: 2

Both the gain and spill hurt are in Doom shaders which is similiar
to what we see on radeonsi ironically the Doom Vulkan shaders are
the most helped by this change.

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>