On Mon, Sep 29, 2014 at 9:50 AM, Matt Turner <matts...@gmail.com> wrote:
> On Fri, Sep 26, 2014 at 12:24 PM, Jason Ekstrand <ja...@jlekstrand.net>
> wrote:
> > This commit reworks copy propagation a bit to support propagating the
> > copying of partial registers. This comes up every time we have pull
> > constants because we do a pull constant read immediately followed by a
> move
> > to splat the one component of the out to 8 or 16-wide. This allows us to
> > eliminate the copy and simply use the one component of the register.
> >
> > Shader DB results:
> >
> > total instructions in shared programs: 5044937 -> 5044428 (-0.01%)
> > instructions in affected programs: 66112 -> 65603 (-0.77%)
> > GAINED: 0
> > LOST: 0
> >
> > Signed-off-by: Jason Ekstrand <jason.ekstr...@intel.com>
> > ---
> > src/mesa/drivers/dri/i965/brw_fs.h | 1 +
> > .../drivers/dri/i965/brw_fs_copy_propagation.cpp | 83
> ++++++++++++++++------
> > 2 files changed, 64 insertions(+), 20 deletions(-)
> >
> > diff --git a/src/mesa/drivers/dri/i965/brw_fs.h
> b/src/mesa/drivers/dri/i965/brw_fs.h
> > index 50b5fc1..9b63114 100644
> > --- a/src/mesa/drivers/dri/i965/brw_fs.h
> > +++ b/src/mesa/drivers/dri/i965/brw_fs.h
> > @@ -337,6 +337,7 @@ public:
> > bool opt_cse_local(bblock_t *block);
> > bool opt_copy_propagate();
> > bool try_copy_propagate(fs_inst *inst, int arg, acp_entry *entry);
> > + bool try_constant_propagate(fs_inst *inst, acp_entry *entry);
> > bool opt_copy_propagate_local(void *mem_ctx, bblock_t *block,
> > exec_list *acp);
> > void opt_drop_redundant_mov_to_flags();
> > diff --git a/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp
> b/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp
> > index e5816df..a97dc04 100644
> > --- a/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp
> > +++ b/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp
> > @@ -277,24 +277,30 @@ is_logic_op(enum opcode opcode)
> > bool
> > fs_visitor::try_copy_propagate(fs_inst *inst, int arg, acp_entry *entry)
> > {
> > + if (inst->src[arg].file != GRF)
> > + return false;
> > +
> > if (entry->src.file == IMM)
> > return false;
> > + assert(entry->src.file == GRF || entry->src.file == UNIFORM);
> >
> > if (entry->opcode == SHADER_OPCODE_LOAD_PAYLOAD &&
> > inst->opcode == SHADER_OPCODE_LOAD_PAYLOAD)
> > return false;
> >
> > - /* Bail if inst is reading more than entry is writing. */
> > - if ((inst->regs_read(this, arg) * inst->src[arg].stride *
> > - type_sz(inst->src[arg].type)) > type_sz(entry->dst.type))
> > + assert(entry->dst.file == GRF);
> > + if (inst->src[arg].reg != entry->dst.reg)
> > return false;
> >
> > - if (inst->src[arg].file != entry->dst.file ||
> > - inst->src[arg].reg != entry->dst.reg ||
> > - inst->src[arg].reg_offset != entry->dst.reg_offset ||
> > - inst->src[arg].subreg_offset != entry->dst.subreg_offset) {
> > + /* Bail if inst is reading a range that isn't contained in the range
> > + * that entry is writing.
> > + */
> > + int reg_size = dispatch_width * sizeof(float);
> > + if (inst->src[arg].reg_offset < entry->dst.reg_offset ||
> > + (inst->src[arg].reg_offset * reg_size +
> inst->src[arg].subreg_offset +
> > + inst->regs_read(this, arg) * inst->src[arg].stride * reg_size) >
> > + (entry->dst.reg_offset + 1) * reg_size)
> > return false;
> > - }
> >
> > /* See resolve_ud_negate() and comment in brw_fs_emit.cpp. */
> > if (inst->conditional_mod &&
> > @@ -361,11 +367,39 @@ fs_visitor::try_copy_propagate(fs_inst *inst, int
> arg, acp_entry *entry)
> >
> > inst->src[arg].file = entry->src.file;
> > inst->src[arg].reg = entry->src.reg;
> > - inst->src[arg].reg_offset = entry->src.reg_offset;
> > - inst->src[arg].subreg_offset = entry->src.subreg_offset;
> > inst->src[arg].stride *= entry->src.stride;
> > inst->saturate = inst->saturate || entry->saturate;
> >
> > + switch (entry->src.file) {
> > + case BAD_FILE:
> > + case HW_REG:
> > + case UNIFORM:
> > + inst->src[arg].reg_offset = entry->src.reg_offset;
> > + inst->src[arg].subreg_offset = entry->src.subreg_offset;
> > + break;
> > + case GRF:
> > + {
> > + /* In this case, we have to deal with mapping parts of vgrfs to
> > + * other parts of vgrfs so we have to do some reg_offset magic.
> > + */
> > +
> > + /* Compute the offset of inst->src[arg] relative to inst->dst
> */
> > + assert(entry->dst.subreg_offset == 0);
> > + int rel_offset = inst->src[arg].reg_offset -
> entry->dst.reg_offset;
> > + int rel_suboffset = inst->src[arg].subreg_offset;
> > +
> > + /* Compute the final register offset (in bytes) */
> > + int offset = entry->src.reg_offset * reg_size +
> entry->src.subreg_offset;
> > + offset += rel_offset * reg_size + rel_suboffset;
> > + inst->src[arg].reg_offset = offset / reg_size;
> > + inst->src[arg].subreg_offset = offset % reg_size;
> > + }
> > + break;
> > + default:
> > + unreachable("Invalid register file");
> > + break;
> > + }
> > +
> > if (!inst->src[arg].abs) {
> > inst->src[arg].abs = entry->src.abs;
> > inst->src[arg].negate ^= entry->src.negate;
> > @@ -375,9 +409,8 @@ fs_visitor::try_copy_propagate(fs_inst *inst, int
> arg, acp_entry *entry)
> > }
> >
> >
> > -static bool
> > -try_constant_propagate(struct brw_context *brw, fs_inst *inst,
> > - acp_entry *entry)
> > +bool
> > +fs_visitor::try_constant_propagate(fs_inst *inst, acp_entry *entry)
> > {
> > bool progress = false;
> >
> > @@ -385,12 +418,22 @@ try_constant_propagate(struct brw_context *brw,
> fs_inst *inst,
> > return false;
> >
> > for (int i = inst->sources - 1; i >= 0; i--) {
> > - if (inst->src[i].file != entry->dst.file ||
> > - inst->src[i].reg != entry->dst.reg ||
> > - inst->src[i].reg_offset != entry->dst.reg_offset ||
> > - inst->src[i].subreg_offset != entry->dst.subreg_offset ||
> > - inst->src[i].type != entry->dst.type ||
> > - inst->src[i].stride > 1)
> > + if (inst->src[i].file != GRF)
> > + continue;
> > +
> > + assert(entry->dst.file == GRF);
> > + if (inst->src[i].reg != entry->dst.reg ||
> > + inst->src[i].type != entry->dst.type)
> > + continue;
> > +
> > + /* Bail if inst is reading a range that isn't contained in the
> range
> > + * that entry is writing.
> > + */
> > + int reg_size = dispatch_width * sizeof(float);
> > + if (inst->src[i].reg_offset < entry->dst.reg_offset ||
> > + (inst->src[i].reg_offset * reg_size +
> inst->src[i].subreg_offset +
> > + inst->regs_read(this, i) * inst->src[i].stride * reg_size) >
> > + (entry->dst.reg_offset + 1) * reg_size)
> > continue;
>
> Does this bit, the constant propagation code, actually benefit from
> this? I guess it'd let an immediate loaded with a mov(16) be constant
> propagated into two SIMD8 instructions? That seems plausible, I was
> just a little surprised at first.
>
Yes, that's exactly what it's for
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