SPIRV-Cross/reference/shaders/frag/complex-expression-in-access-chain.frag
Hans-Kristian Arntzen acae607703 Register implied expression reads in OpLoad/OpAccessChain.
This is required to avoid relying on complex sub-expression elimination
in compilers, and generates cleaner code.

The problem case is if a complex expression is used in an access chain,
like:

Composite comp = buffer[texture(...)];
vec4 a = comp.a + comp.b + comp.c;

Before, we did not have common subexpression tracking for
OpLoad/OpAccessChain, so we easily ended up with code like:

vec4 a = buffer[texture(...)].a + buffer[texture(...)].b + buffer[texture(...)].c;

A good compiler will optimize this, but we should not rely on it, and
forcing texture(...) to a temporary also looks better.

The solution is to add a vector "implied_expression_reads", which works
similarly to expression_dependencies. We also need an extra mechanism in
to_expression which lets us skip expression read checking and do it
later. E.g. for expr -> access chain -> load, we should only trigger
a read of expr when using the loaded expression.
2019-01-04 14:56:12 +01:00

25 lines
567 B
GLSL

#version 310 es
precision mediump float;
precision highp int;
layout(binding = 0, std430) buffer UBO
{
vec4 results[1024];
} _34;
layout(binding = 1) uniform highp isampler2D Buf;
layout(location = 0) flat in mediump int vIn;
layout(location = 1) flat in mediump int vIn2;
layout(location = 0) out vec4 FragColor;
void main()
{
mediump ivec4 coords = texelFetch(Buf, ivec2(gl_FragCoord.xy), 0);
vec4 foo = _34.results[coords.x % 16];
mediump int c = vIn * vIn;
mediump int d = vIn2 * vIn2;
FragColor = (foo + foo) + _34.results[c + d];
}