functions_blocks.md

Functions and Blocks

Similar to LLVM, SPIR-V is made of up of Blocks. The Blocks can together form a Function.

Using the following GLSL example to help explain the concept:

float add(float a, float b) {
    return a + b;
}

void main() {
    float c = add(in_a, in_b);

    if (c > 0.0) {
        out_data = 1.0;
    } else {
        out_data = -1.0;
    }
}

will produce the following SPIR-V disassembly

Function Block

Every function is starts with OpFunction and ends with the OpFunctionEnd instruction.

The OpFunctionCall can be used to jump to another function.

Blocks

A function may contain many Blocks. Every block first starts with a OpLabel and ends with a Block Termination Instruction.