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mesa: Add an optimization path to remove use of pointless MOVs.

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GLSL code such as:
	vec4 result = {0, 1, 0, 0};
	gl_FragColor = result;

emits code like:
  0: MOV TEMP[0], CONST[0];
  1: MOV OUTPUT[1], TEMP[0];

and this replaces it with:
  0: MOV TEMP[0], CONST[0];
  1: MOV OUTPUT[1], CONST[0];

Even when the dead code eliminator fails to clean up a now-useless MOV
instruction (since it doesn't do live/dead ranges), this should at reduce
dependencies.
This commit is contained in:
Eric Anholt 2009-05-16 01:47:44 -07:00
parent ee0a9e6e10
commit e4e312d493
1 changed files with 83 additions and 1 deletions
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84
src/mesa/shader/prog_optimize.c
View file

@ -38,7 +38,6 @@
static GLboolean dbg = GL_FALSE; static GLboolean dbg = GL_FALSE;
/** /**
* In 'prog' remove instruction[i] if removeFlags[i] == TRUE. * In 'prog' remove instruction[i] if removeFlags[i] == TRUE.
* \return number of instructions removed * \return number of instructions removed
@ -354,6 +353,87 @@ find_next_temp_use(const struct gl_program *prog, GLuint start, GLuint index)
} }
/**
* Try to remove use of extraneous MOV instructions, to free them up for dead
* code removal.
*/
static void
_mesa_remove_extra_move_use(struct gl_program *prog)
{
GLuint i;
if (dbg) {
_mesa_printf("Optimize: Begin remove extra move use\n");
_mesa_print_program(prog);
}
/*
* Look for sequences such as this:
* MOV tmpX, arg0;
* FOO tmpY, tmpX, arg1;
* and convert into:
* MOV tmpX, arg0;
* FOO tmpY, arg0, arg1;
*/
for (i = 0; i < prog->NumInstructions - 1; i++) {
const struct prog_instruction *mov = prog->Instructions + i;
struct prog_instruction *inst2 = prog->Instructions + i + 1;
int arg;
if (mov->Opcode != OPCODE_MOV ||
mov->DstReg.File != PROGRAM_TEMPORARY ||
mov->DstReg.RelAddr ||
mov->DstReg.CondMask != COND_TR ||
mov->SaturateMode != SATURATE_OFF)
continue;
for (arg = 0; arg < _mesa_num_inst_src_regs(inst2->Opcode); arg++) {
int comp;
if (inst2->SrcReg[arg].File != mov->DstReg.File ||
inst2->SrcReg[arg].Index != mov->DstReg.Index ||
inst2->SrcReg[arg].RelAddr ||
inst2->SrcReg[arg].Abs)
continue;
/* Check that all the sources for this arg of inst2 come from inst1
* or constants.
*/
for (comp = 0; comp < 4; comp++) {
int src_swz = GET_SWZ(inst2->SrcReg[arg].Swizzle, comp);
/* If the MOV didn't write that channel, can't use it. */
if (src_swz <= SWIZZLE_W &&
(mov->DstReg.WriteMask & (1 << src_swz)) == 0)
break;
}
if (comp != 4)
continue;
/* Adjust the swizzles of inst2 to point at MOV's source */
for (comp = 0; comp < 4; comp++) {
int inst2_swz = GET_SWZ(inst2->SrcReg[arg].Swizzle, comp);
if (inst2_swz <= SWIZZLE_W) {
GLuint s = GET_SWZ(mov->SrcReg[0].Swizzle, inst2_swz);
inst2->SrcReg[arg].Swizzle &= ~(7 << (3 * comp));
inst2->SrcReg[arg].Swizzle |= s << (3 * comp);
inst2->SrcReg[arg].Negate ^= (((mov->SrcReg[0].Negate >>
inst2_swz) & 0x1) << comp);
}
}
inst2->SrcReg[arg].File = mov->SrcReg[0].File;
inst2->SrcReg[arg].Index = mov->SrcReg[0].Index;
}
}
if (dbg) {
_mesa_printf("Optimize: End remove extra move use.\n");
/*_mesa_print_program(prog);*/
}
}
/** /**
* Try to remove extraneous MOV instructions from the given program. * Try to remove extraneous MOV instructions from the given program.
*/ */
@ -851,6 +931,8 @@ _mesa_reallocate_registers(struct gl_program *prog)
void void
_mesa_optimize_program(GLcontext *ctx, struct gl_program *program) _mesa_optimize_program(GLcontext *ctx, struct gl_program *program)
{ {
_mesa_remove_extra_move_use(program);
if (1) if (1)
_mesa_remove_dead_code(program); _mesa_remove_dead_code(program);