[Mesa-dev] [RFC PATCH 1/5] i965: Add writes_accumulator flag
Juha-Pekka Heikkila
juhapekka.heikkila at gmail.com
Fri Mar 21 07:33:18 PDT 2014
Our hardware has an "accumulator" register, which can be used to store
intermediate results across multiple instructions. Many instructions
can implicitly write a value to the accumulator in addition to their
normal destination register. This is enabled by the "AccWrEn" flag.
This patch introduces a new flag, inst->writes_accumulator, which
allows us to express the AccWrEn notion in the IR. It also creates a
n ALU2_ACC macro to easily define emitters for instructions that
implicitly write the accumulator.
Previously, we only supported implicit accumulator writes from the
ADDC, SUBB, and MACH instructions. We always enabled them on those
instructions, and left them disabled for other instructions.
To take advantage of the MAC (multiply-accumulate) instruction, we
need to be able to set AccWrEn on other types of instructions.
Signed-off-by: Juha-Pekka Heikkila <juhapekka.heikkila at gmail.com>
---
src/mesa/drivers/dri/i965/brw_fs.cpp | 34 +++++++++++-------------
src/mesa/drivers/dri/i965/brw_fs_generator.cpp | 7 +----
src/mesa/drivers/dri/i965/brw_shader.cpp | 3 +++
src/mesa/drivers/dri/i965/brw_shader.h | 1 +
src/mesa/drivers/dri/i965/brw_vec4.cpp | 15 +----------
src/mesa/drivers/dri/i965/brw_vec4_generator.cpp | 7 +----
src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp | 21 +++++++++++----
7 files changed, 39 insertions(+), 49 deletions(-)
diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
index 27cf0f6..107d9e6 100644
--- a/src/mesa/drivers/dri/i965/brw_fs.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
@@ -64,6 +64,8 @@ fs_inst::init()
/* This will be the case for almost all instructions. */
this->regs_written = 1;
+
+ this->writes_accumulator = false;
}
fs_inst::fs_inst()
@@ -151,6 +153,15 @@ fs_inst::fs_inst(enum opcode opcode, fs_reg dst,
return new(mem_ctx) fs_inst(BRW_OPCODE_##op, dst, src0, src1); \
}
+#define ALU2_ACC(op) \
+ fs_inst * \
+ fs_visitor::op(fs_reg dst, fs_reg src0, fs_reg src1) \
+ { \
+ fs_inst *inst = new(mem_ctx) fs_inst(BRW_OPCODE_##op, dst, src0, src1);\
+ inst->writes_accumulator = true; \
+ return inst; \
+ }
+
#define ALU3(op) \
fs_inst * \
fs_visitor::op(fs_reg dst, fs_reg src0, fs_reg src1, fs_reg src2) \
@@ -166,7 +177,7 @@ ALU1(RNDE)
ALU1(RNDZ)
ALU2(ADD)
ALU2(MUL)
-ALU2(MACH)
+ALU2_ACC(MACH)
ALU2(AND)
ALU2(OR)
ALU2(XOR)
@@ -182,8 +193,8 @@ ALU1(FBH)
ALU1(FBL)
ALU1(CBIT)
ALU3(MAD)
-ALU2(ADDC)
-ALU2(SUBB)
+ALU2_ACC(ADDC)
+ALU2_ACC(SUBB)
ALU2(SEL)
/** Gen4 predicated IF. */
@@ -2103,21 +2114,8 @@ fs_visitor::dead_code_eliminate()
}
if (dead) {
- /* Don't dead code eliminate instructions that write to the
- * accumulator as a side-effect. Instead just set the destination
- * to the null register to free it.
- */
- switch (inst->opcode) {
- case BRW_OPCODE_ADDC:
- case BRW_OPCODE_SUBB:
- case BRW_OPCODE_MACH:
- inst->dst = fs_reg(retype(brw_null_reg(), inst->dst.type));
- break;
- default:
- inst->remove();
- progress = true;
- break;
- }
+ inst->remove();
+ progress = true;
}
}
diff --git a/src/mesa/drivers/dri/i965/brw_fs_generator.cpp b/src/mesa/drivers/dri/i965/brw_fs_generator.cpp
index e590bdf..1cf35b4 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_generator.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_generator.cpp
@@ -1411,6 +1411,7 @@ fs_generator::generate_code(exec_list *instructions, FILE *dump_file)
brw_set_flag_reg(p, 0, inst->flag_subreg);
brw_set_saturate(p, inst->saturate);
brw_set_mask_control(p, inst->force_writemask_all);
+ brw_set_acc_write_control(p, inst->writes_accumulator);
if (inst->force_uncompressed || dispatch_width == 8) {
brw_set_compression_control(p, BRW_COMPRESSION_NONE);
@@ -1434,9 +1435,7 @@ fs_generator::generate_code(exec_list *instructions, FILE *dump_file)
brw_AVG(p, dst, src[0], src[1]);
break;
case BRW_OPCODE_MACH:
- brw_set_acc_write_control(p, 1);
brw_MACH(p, dst, src[0], src[1]);
- brw_set_acc_write_control(p, 0);
break;
case BRW_OPCODE_MAD:
@@ -1540,15 +1539,11 @@ fs_generator::generate_code(exec_list *instructions, FILE *dump_file)
break;
case BRW_OPCODE_ADDC:
assert(brw->gen >= 7);
- brw_set_acc_write_control(p, 1);
brw_ADDC(p, dst, src[0], src[1]);
- brw_set_acc_write_control(p, 0);
break;
case BRW_OPCODE_SUBB:
assert(brw->gen >= 7);
- brw_set_acc_write_control(p, 1);
brw_SUBB(p, dst, src[0], src[1]);
- brw_set_acc_write_control(p, 0);
break;
case BRW_OPCODE_BFE:
diff --git a/src/mesa/drivers/dri/i965/brw_shader.cpp b/src/mesa/drivers/dri/i965/brw_shader.cpp
index 407319b..7a26755 100644
--- a/src/mesa/drivers/dri/i965/brw_shader.cpp
+++ b/src/mesa/drivers/dri/i965/brw_shader.cpp
@@ -666,6 +666,9 @@ backend_instruction::can_do_saturate()
bool
backend_instruction::has_side_effects() const
{
+ if (this->writes_accumulator)
+ return true;
+
switch (opcode) {
case SHADER_OPCODE_UNTYPED_ATOMIC:
return true;
diff --git a/src/mesa/drivers/dri/i965/brw_shader.h b/src/mesa/drivers/dri/i965/brw_shader.h
index 086d042..e0f6a06 100644
--- a/src/mesa/drivers/dri/i965/brw_shader.h
+++ b/src/mesa/drivers/dri/i965/brw_shader.h
@@ -59,6 +59,7 @@ public:
uint8_t predicate;
bool predicate_inverse;
+ bool writes_accumulator; /**< instruction implicitly writes accumulator */
};
enum instruction_scheduler_mode {
diff --git a/src/mesa/drivers/dri/i965/brw_vec4.cpp b/src/mesa/drivers/dri/i965/brw_vec4.cpp
index 87825f1..473f26c 100644
--- a/src/mesa/drivers/dri/i965/brw_vec4.cpp
+++ b/src/mesa/drivers/dri/i965/brw_vec4.cpp
@@ -333,20 +333,7 @@ vec4_visitor::dead_code_eliminate()
if (inst->dst.file == GRF && !inst->has_side_effects()) {
assert(this->virtual_grf_end[inst->dst.reg] >= pc);
if (this->virtual_grf_end[inst->dst.reg] == pc) {
- /* Don't dead code eliminate instructions that write to the
- * accumulator as a side-effect. Instead just set the destination
- * to the null register to free it.
- */
- switch (inst->opcode) {
- case BRW_OPCODE_ADDC:
- case BRW_OPCODE_SUBB:
- case BRW_OPCODE_MACH:
- inst->dst = dst_reg(retype(brw_null_reg(), inst->dst.type));
- break;
- default:
- inst->remove();
- break;
- }
+ inst->remove();
progress = true;
}
}
diff --git a/src/mesa/drivers/dri/i965/brw_vec4_generator.cpp b/src/mesa/drivers/dri/i965/brw_vec4_generator.cpp
index a74514f..5f85d31 100644
--- a/src/mesa/drivers/dri/i965/brw_vec4_generator.cpp
+++ b/src/mesa/drivers/dri/i965/brw_vec4_generator.cpp
@@ -971,9 +971,7 @@ vec4_generator::generate_vec4_instruction(vec4_instruction *instruction,
brw_MUL(p, dst, src[0], src[1]);
break;
case BRW_OPCODE_MACH:
- brw_set_acc_write_control(p, 1);
brw_MACH(p, dst, src[0], src[1]);
- brw_set_acc_write_control(p, 0);
break;
case BRW_OPCODE_MAD:
@@ -1077,15 +1075,11 @@ vec4_generator::generate_vec4_instruction(vec4_instruction *instruction,
break;
case BRW_OPCODE_ADDC:
assert(brw->gen >= 7);
- brw_set_acc_write_control(p, 1);
brw_ADDC(p, dst, src[0], src[1]);
- brw_set_acc_write_control(p, 0);
break;
case BRW_OPCODE_SUBB:
assert(brw->gen >= 7);
- brw_set_acc_write_control(p, 1);
brw_SUBB(p, dst, src[0], src[1]);
- brw_set_acc_write_control(p, 0);
break;
case BRW_OPCODE_BFE:
@@ -1317,6 +1311,7 @@ vec4_generator::generate_code(exec_list *instructions)
brw_set_predicate_inverse(p, inst->predicate_inverse);
brw_set_saturate(p, inst->saturate);
brw_set_mask_control(p, inst->force_writemask_all);
+ brw_set_acc_write_control(p, inst->writes_accumulator);
unsigned pre_emit_nr_insn = p->nr_insn;
diff --git a/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp b/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
index c73e58d..33df5d3 100644
--- a/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
+++ b/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
@@ -42,6 +42,7 @@ vec4_instruction::vec4_instruction(vec4_visitor *v,
this->force_writemask_all = false;
this->no_dd_clear = false;
this->no_dd_check = false;
+ this->writes_accumulator = false;
this->conditional_mod = BRW_CONDITIONAL_NONE;
this->sampler = 0;
this->texture_offset = 0;
@@ -113,7 +114,7 @@ vec4_visitor::emit(enum opcode opcode)
vec4_visitor::op(dst_reg dst, src_reg src0) \
{ \
return new(mem_ctx) vec4_instruction(this, BRW_OPCODE_##op, dst, \
- src0); \
+ src0); \
}
#define ALU2(op) \
@@ -121,7 +122,17 @@ vec4_visitor::emit(enum opcode opcode)
vec4_visitor::op(dst_reg dst, src_reg src0, src_reg src1) \
{ \
return new(mem_ctx) vec4_instruction(this, BRW_OPCODE_##op, dst, \
- src0, src1); \
+ src0, src1); \
+ }
+
+#define ALU2_ACC(op) \
+ vec4_instruction * \
+ vec4_visitor::op(dst_reg dst, src_reg src0, src_reg src1) \
+ { \
+ vec4_instruction *inst = new(mem_ctx) vec4_instruction(this, \
+ BRW_OPCODE_##op, dst, src0, src1); \
+ inst->writes_accumulator = true; \
+ return inst; \
}
#define ALU3(op) \
@@ -143,7 +154,7 @@ ALU1(F32TO16)
ALU1(F16TO32)
ALU2(ADD)
ALU2(MUL)
-ALU2(MACH)
+ALU2_ACC(MACH)
ALU2(AND)
ALU2(OR)
ALU2(XOR)
@@ -162,8 +173,8 @@ ALU1(FBH)
ALU1(FBL)
ALU1(CBIT)
ALU3(MAD)
-ALU2(ADDC)
-ALU2(SUBB)
+ALU2_ACC(ADDC)
+ALU2_ACC(SUBB)
/** Gen4 predicated IF. */
vec4_instruction *
--
1.8.1.2
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