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i965/fs: Add support for removing MOV.NZ instructions. 

For some reason, we occasionally write the flag register with a MOV.NZ
instruction:

   add(8)          g25<1>F         -g6<0,1,0>F     g15<8,8,1>F
   cmp.l.f0(8)     g26<1>D         g25<8,8,1>F     0F
   mov.nz.f0(8)    null            g26<8,8,1>D

A MOV.NZ instruction on the result of a CMP is like comparing for
equality with true in C. It's useless. Removing it allows us to
generate:

   add.l.f0(8)     null            -g6<0,1,0>F     g15<8,8,1>F

total instructions in shared programs: 5955701 -> 5951657 (-0.07%)
instructions in affected programs:     302910 -> 298866 (-1.34%)
GAINED:                                1
LOST:                                  0

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
This commit is contained in:
Matt Turner 2014-12-30 17:19:41 -08:00
parent 9a3a294224
commit 40ae302a3c
2 changed files with 52 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

23
src/mesa/drivers/dri/i965/brw_fs_cmod_propagation.cpp
View File

@ -57,12 +57,20 @@ opt_cmod_propagation_local(fs_visitor *v, bblock_t *block)
foreach_inst_in_block_reverse_safe(fs_inst, inst, block) {
ip--;
if (inst->opcode != BRW_OPCODE_CMP ||
if ((inst->opcode != BRW_OPCODE_CMP &&
inst->opcode != BRW_OPCODE_MOV) ||
inst->predicate != BRW_PREDICATE_NONE ||
!inst->dst.is_null() ||
inst->src[0].file != GRF ||
inst->src[0].abs ||
!inst->src[1].is_zero())
inst->src[0].abs)
continue;
if (inst->opcode == BRW_OPCODE_CMP && !inst->src[1].is_zero())
continue;
if (inst->opcode == BRW_OPCODE_MOV &&
(inst->conditional_mod != BRW_CONDITIONAL_NZ ||
inst->src[0].negate))
continue;
bool read_flag = false;
@ -73,6 +81,15 @@ opt_cmod_propagation_local(fs_visitor *v, bblock_t *block)
scan_inst->dst.reg_offset != inst->src[0].reg_offset)
break;
if (inst->opcode == BRW_OPCODE_MOV) {
if (!scan_inst->writes_flag())
break;
inst->remove(block);
progress = true;
break;
}
enum brw_conditional_mod cond =
inst->src[0].negate ? brw_swap_cmod(inst->conditional_mod)
: inst->conditional_mod;

32
src/mesa/drivers/dri/i965/test_fs_cmod_propagation.cpp
View File

@ -383,3 +383,35 @@ TEST_F(cmod_propagation_test, negate)
EXPECT_EQ(BRW_OPCODE_ADD, instruction(block0, 0)->opcode);
EXPECT_EQ(BRW_CONDITIONAL_LE, instruction(block0, 0)->conditional_mod);
}
TEST_F(cmod_propagation_test, movnz)
{
fs_reg dest = v->vgrf(glsl_type::float_type);
fs_reg src0 = v->vgrf(glsl_type::float_type);
fs_reg src1 = v->vgrf(glsl_type::float_type);
v->emit(BRW_OPCODE_CMP, dest, src0, src1)
->conditional_mod = BRW_CONDITIONAL_GE;
v->emit(BRW_OPCODE_MOV, v->reg_null_f, dest)
->conditional_mod = BRW_CONDITIONAL_NZ;
/* = Before =
*
* 0: cmp.ge.f0(8) dest src0 src1
* 1: mov.nz.f0(8) null dest
*
* = After =
* 0: cmp.ge.f0(8) dest src0 src1
*/
v->calculate_cfg();
bblock_t *block0 = v->cfg->blocks[0];
EXPECT_EQ(0, block0->start_ip);
EXPECT_EQ(1, block0->end_ip);
EXPECT_TRUE(cmod_propagation(v));
EXPECT_EQ(0, block0->start_ip);
EXPECT_EQ(0, block0->end_ip);
EXPECT_EQ(BRW_OPCODE_CMP, instruction(block0, 0)->opcode);
EXPECT_EQ(BRW_CONDITIONAL_GE, instruction(block0, 0)->conditional_mod);
}