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OpenGL & Vulkan

Journeyman III
Journeyman III

s_load_dwordx16 not emitted


I am looking at the output of the compilation of this shader in RGA:

#version 450

#pragma shader_stage(compute)

layout (push_constant) uniform PC { mat4 a; };

layout (std430, binding = 0) buffer BufferIn { vec4[] data_in; };

layout (local_size_x = 64) in;

void main() {

   data_in[gl_LocalInvocationID.x] = a * vec4(data_in[gl_LocalInvocationID.x]);


which results in (for RDNA, but GCN is very similar)

s_getpc_b64 s[0:1]

s_mov_b32 s3, s1

s_load_dword s0, s[2:3], 0x40

s_waitcnt lgkmcnt(0)

s_load_dwordx4 s[4:7], s[0:1], 0x00

v_lshlrev_b32 v0, 4, v0

s_waitcnt lgkmcnt(0)

buffer_load_dwordx4 v[1:4], v0, s[4:7], 0 offen

s_load_dwordx8 s[8:15], s[2:3], 0x00

s_load_dwordx8 s[16:23], s[2:3], 0x20

s_waitcnt vmcnt(0) & lgkmcnt(0)

v_mul_f32 v5, s8, v1

v_mul_f32 v6, s9, v1

v_mul_f32 v7, s10, v1

v_mul_f32 v1, s11, v1

v_fmac_f32 v5, s12, v2

v_fmac_f32 v6, s13, v2

v_fmac_f32 v7, s14, v2

v_fmac_f32 v1, s15, v2

v_fmac_f32 v5, s16, v3

v_fmac_f32 v6, s17, v3

v_fmac_f32 v7, s18, v3

v_fmac_f32 v1, s19, v3

v_fmac_f32 v5, s20, v4

v_fmac_f32 v6, s21, v4

v_fmac_f32 v7, s22, v4

v_fma_f32 v8, s23, v4, v1

buffer_store_dwordx4 v[5:8], v0, s[4:7], 0 offen glc


What is the reason that the compiler emits 2x s_load_dwordx8 instead of one s_load_dwordx16?

Seems like both source and destination are consecutive.

Thank you in advance!

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Re: s_load_dwordx16 not emitted

It's related to the number of the fragment buffer of your card. As your card has only 8 fragment buffers, one load OP can only fetch 8 samples' result, so 16 samples are divided into 2 * 8 samples.

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