render/vulkan: Optimize vertex shader
This ends up being a horrible global load:
s_getpc_b64 s[4:5] // 000000000000: BE841C80
v_add_u32 v0, s2, v0 // 000000000004: 68000002
v_sub_co_u32 v1, vcc, 0, v0 // 000000000008: 34020080
v_max_i32 v1, v0, v1 // 00000000000C: 1A020300
v_and_b32 v1, 3, v1 // 000000000010: 26020283
v_cmp_lt_i32 s[0:1], v0, 0 // 000000000014: D0C10000 00010100
v_sub_co_u32 v0, vcc, 0, v1 // 00000000001C: 34000280
v_cndmask_b32 v0, v1, v0, s[0:1] // 000000000020: D1000000 00020101
v_lshlrev_b32 v1, 3, v0 // 000000000028: 24020083
v_mad_u32_u24 v0, v0, 8, 4 // 00000000002C: D1C30000 02111100
v_min_u32 v1, 32, v1 // 000000000034: 1C0202A0
v_min_u32 v0, 32, v0 // 000000000038: 1C0000A0
s_getpc_b64 s[0:1] // 00000000003C: BE801C00
s_add_u32 s0, s0, 0x0000003c // 000000000040: 8000FF00 0000003C
s_addc_u32 s1, s1, 0 // 000000000048: 82018001
global_load_dword v1, v[1:2], s[0:1] // 00000000004C: DC508000 01000001
global_load_dword v0, v[0:1], s[0:1] // 000000000054: DC508000 00000000
v_mov_b32 v2, 0 // 00000000005C: 7E040280
v_mov_b32 v3, 1.0 // 000000000060: 7E0602F2
s_waitcnt vmcnt(0) // 000000000064: BF8C0F70
exp pos0, v1, v0, v2, v3 done // 000000000068: C40008CF 03020001
exp param0, off, off, off, off // 000000000070: C4000200 00000000
s_endpgm // 000000000078: BF810000
v_cndmask_b32 v0, s0, v0, vcc // 00000000007C: 00000000
v_cndmask_b32 v0, s0, v0, vcc // 000000000080: 00000000
v_add_f16 v192, s0, v0 // 000000000084: 3F800000
v_cndmask_b32 v0, s0, v0, vcc // 000000000088: 00000000
v_add_f16 v192, s0, v0 // 00000000008C: 3F800000
v_add_f16 v192, s0, v0 // 000000000090: 3F800000
v_cndmask_b32 v0, s0, v0, vcc // 000000000094: 00000000
v_add_f16 v192, s0, v0 // 000000000098: 3F800000
v_cndmask_b32 v0, s0, v0, vcc // 00000000009C: 00000000
With some bit magic, we can get something much nicer:
v_add_u32 v0, s2, v0 // 000000000000: 68000002
v_add_u32 v1, 1, v0 // 000000000004: 68020081
v_and_b32 v1, 2, v1 // 000000000008: 26020282
v_cvt_f32_i32 v1, v1 // 00000000000C: 7E020B01
v_mul_f32 v1, 0.5, v1 // 000000000010: 0A0202F0
v_and_b32 v0, 2, v0 // 000000000014: 26000082
v_cvt_f32_i32 v0, v0 // 000000000018: 7E000B00
v_mul_f32 v0, 0.5, v0 // 00000000001C: 0A0000F0
v_mov_b32 v2, 0 // 000000000020: 7E040280
v_mov_b32 v3, 1.0 // 000000000024: 7E0602F2
exp pos0, v1, v0, v2, v3 done // 000000000028: C40008CF 03020001
exp param0, off, off, off, off // 000000000030: C4000200 00000000
s_endpgm // 000000000038: BF810000
The above output was based on just shoving it in ShaderPlayground -- I was not able to use pipeline feedback as I was unable to get RenderDoc working due to the EXT_physical_device_drm requirement.
I additionally considered using >> 1 instead of * 0.5, but AMD has dedicated modifiers to merge a * 0.5, * 2.0, etc in a single instruction. (Albeit, not taken advantage of in the code above, but might with ACO)
Signed-off-by: Joshua Ashton <joshua@froggi.es>
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