问题
Is there a maximum number of assembly language instructions to be loaded into the fragment program unit? I have an algorithm on to port from cpu to gpu and apparently it doesn't fit on the gpu.
回答1:
There are several hard and soft limits, some of which are not immediately obvious:
- Instruction slots: The total number of instructions that the hardware can accomodate in local memory.
- Executed instructions: The maximum number of instructions that will execute (including instructions that run several times in a loop)
- A single GLSL instruction can map to a dozen or more instructions
- Several GLSL instructions can map to a single instruction depending on the optimizer's quality (e.g. multiply-add, dot, lerp)
- Limited temp registers (only 32) may require more instructions than necessary on pre-SM4 hardware (no such problem with 4096).
- Swizzling usually does not cost extra instructions nowadays, but does on some older hardware, and may in some situations on some hardware (esp. gl_FragColor is such a candidate)
- Regardless of actual instructions, OpenGL 2.0 compatible hardware is limited to 8 dependent texture fetches (unlimited on hardware that can do OpenGL 2.1 or better)
You have these guaranteed minimums (most cards have more):
- 512 instruction slots for vertex and pixel shaders on OpenGL 2.x (SM3) capable hardware
- 65536 executed instructions
- 4096 vertex and 65536 pixel shader instruction slots on 3.x (SM4) hardware
- 65536 executed vertex shader instructions, unlimited pixel shader instructions
- At least 24 dynamic branches possible on 2.x (SM3) hardware
- Fully dynamic branching (no limits) on SM4 hardware
- Only conditional move available on SM2.x, everything else must be accomodated by code duplication and loop unrolling, or must fail
回答2:
There is a limit on the maximum amount of instructions a shader can have. As far as I know, it varies from GPU to GPU. If your shader is too large, compilation will generate an error.
来源：https://stackoverflow.com/questions/2617957/glsl-maximum-number-of-instructions