skia2/tests/sksl/runtime/SampleWithConstantMatrix.skvm
Mike Klein ff4decc35e add fast_mul(F32,F32)
This is just like mul(F32,F32) but optimizes 0*x == 0.
Use it in SkSLVMGenerator; sksl already applies this optimization.

PS2 has a sneaky version using % as a fast_mul() operator, and
PS3 has a sneakier version using ** instead.

We could of course write this all out using fast_mul() the long way,
but I found that quickly became difficult to read.

Change-Id: Iae35ce54411abc00e7729e178eb6a10f151a5304
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/368838
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
2021-02-11 01:13:01 +00:00

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9 registers, 24 instructions:
0 r0 = uniform32 ptr0 0
1 r1 = uniform32 ptr0 C
2 r2 = splat 40000000 (2)
3 r0 = trunc r0
4 r1 = mul_i32 r0 r1
5 r0 = splat 1 (1.4012985e-45)
6 r3 = splat 2 (2.8025969e-45)
7 r4 = splat 3 (4.2038954e-45)
loop:
8 r5 = index
9 r5 = mul_f32 r2 r5
10 r5 = trunc r5
11 r5 = add_i32 r5 r1
12 r5 = shl_i32 r5 2
13 r6 = gather32 ptr0 4 r5
14 r7 = add_i32 r5 r0
15 r7 = gather32 ptr0 4 r7
16 r8 = add_i32 r5 r3
17 r8 = gather32 ptr0 4 r8
18 r5 = add_i32 r5 r4
19 r5 = gather32 ptr0 4 r5
20 store32 ptr1 r6
21 store32 ptr2 r7
22 store32 ptr3 r8
23 store32 ptr4 r5