diff options
| -rw-r--r-- | src/mesa/program/prog_optimize.c | 78 |
1 files changed, 78 insertions, 0 deletions
diff --git a/src/mesa/program/prog_optimize.c b/src/mesa/program/prog_optimize.c index acf0f60eae8..11debc485eb 100644 --- a/src/mesa/program/prog_optimize.c +++ b/src/mesa/program/prog_optimize.c @@ -1246,6 +1246,83 @@ print_it(struct gl_context *ctx, struct gl_program *program, const char *txt) { } #endif +/** + * This pass replaces CMP T0, T1 T2 T0 with MOV T0, T2 when the CMP + * instruction is the first instruction to write to register T0. The are + * several lowering passes done in GLSL IR (e.g. branches and + * relative addressing) that create a large number of conditional assignments + * that ir_to_mesa converts to CMP instructions like the one mentioned above. + * + * Here is why this conversion is safe: + * CMP T0, T1 T2 T0 can be expanded to: + * if (T1 < 0.0) + * MOV T0, T2; + * else + * MOV T0, T0; + * + * If (T1 < 0.0) evaluates to true then our replacement MOV T0, T2 is the same + * as the original program. If (T1 < 0.0) evaluates to false, executing + * MOV T0, T0 will store a garbage value in T0 since T0 is uninitialized. + * Therefore, it doesn't matter that we are replacing MOV T0, T0 with MOV T0, T2 + * because any instruction that was going to read from T0 after this was going + * to read a garbage value anyway. + */ +static void +_mesa_simplify_cmp(struct gl_program * program) +{ + GLuint tempWrites[REG_ALLOCATE_MAX_PROGRAM_TEMPS]; + GLuint outputWrites[MAX_PROGRAM_OUTPUTS]; + GLuint i; + + if (dbg) { + printf("Optimize: Begin reads without writes\n"); + _mesa_print_program(program); + } + + for (i = 0; i < REG_ALLOCATE_MAX_PROGRAM_TEMPS; i++) { + tempWrites[i] = 0; + } + + for (i = 0; i < MAX_PROGRAM_OUTPUTS; i++) { + outputWrites[i] = 0; + } + + for (i = 0; i < program->NumInstructions; i++) { + struct prog_instruction *inst = program->Instructions + i; + GLuint prevWriteMask; + + /* Give up if we encounter relative addressing or flow control. */ + if (_mesa_is_flow_control_opcode(inst->Opcode) || inst->DstReg.RelAddr) { + return; + } + + if (inst->DstReg.File == PROGRAM_OUTPUT) { + assert(inst->DstReg.Index < MAX_PROGRAM_OUTPUTS); + prevWriteMask = outputWrites[inst->DstReg.Index]; + outputWrites[inst->DstReg.Index] |= inst->DstReg.WriteMask; + } else if (inst->DstReg.File == PROGRAM_TEMPORARY) { + assert(inst->DstReg.Index < REG_ALLOCATE_MAX_PROGRAM_TEMPS); + prevWriteMask = tempWrites[inst->DstReg.Index]; + tempWrites[inst->DstReg.Index] |= inst->DstReg.WriteMask; + } + + /* For a CMP to be considered a conditional write, the destination + * register and source register two must be the same. */ + if (inst->Opcode == OPCODE_CMP + && !(inst->DstReg.WriteMask & prevWriteMask) + && inst->SrcReg[2].File == inst->DstReg.File + && inst->SrcReg[2].Index == inst->DstReg.Index + && inst->DstReg.WriteMask == get_src_arg_mask(inst, 2, NO_MASK)) { + + inst->Opcode = OPCODE_MOV; + inst->SrcReg[0] = inst->SrcReg[1]; + } + } + if (dbg) { + printf("Optimize: End reads without writes\n"); + _mesa_print_program(program); + } +} /** * Apply optimizations to the given program to eliminate unnecessary @@ -1256,6 +1333,7 @@ _mesa_optimize_program(struct gl_context *ctx, struct gl_program *program) { GLboolean any_change; + _mesa_simplify_cmp(program); /* Stop when no modifications were output */ do { any_change = GL_FALSE; |