[Mesa-dev] [PATCH v2 1/3] i965: Introduce a MOV_INDIRECT opcode.
Kenneth Graunke
kenneth at whitecape.org
Thu Nov 12 20:52:53 PST 2015
On Thursday, November 12, 2015 07:27:31 PM Jason Ekstrand wrote:
> On Wed, Nov 11, 2015 at 12:02 PM, Kenneth Graunke <kenneth at whitecape.org> wrote:
> > The geometry and tessellation control shader stages both read from
> > multiple URB entries (one per vertex). The thread payload contains
> > several URB handles which reference these separate memory segments.
> >
> > In GLSL, these inputs are represented as per-vertex arrays; the
> > outermost array index selects which vertex's inputs to read. This
> > array index does not necessarily need to be constant.
> >
> > To handle that, we need to use indirect addressing on GRFs to select
> > which of the thread payload registers has the appropriate URB handle.
> > (This is before we can even think about applying the pull model!)
> >
> > This patch introduces a new opcode which performs a MOV from a
> > source using VxH indirect addressing (which allows each of the 8
> > SIMD channels to select distinct data.)
> >
> > Based on a patch by Jason Ekstrand.
> >
> > Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
> > ---
> > src/mesa/drivers/dri/i965/brw_defines.h | 9 +++++++
> > src/mesa/drivers/dri/i965/brw_fs.cpp | 24 ++++++++++++++++++
> > src/mesa/drivers/dri/i965/brw_fs.h | 5 ++++
> > src/mesa/drivers/dri/i965/brw_fs_cse.cpp | 1 +
> > src/mesa/drivers/dri/i965/brw_fs_generator.cpp | 34 ++++++++++++++++++++++++++
> > src/mesa/drivers/dri/i965/brw_shader.cpp | 2 ++
> > 6 files changed, 75 insertions(+)
> >
> > Jason,
> >
> > I omitted a few things from your patch:
> >
> > - UNIFORM handling in regs_read() - didn't want to ship it without testing it
> > So you'll need to add this back in when you start using it.
> > - Gen7 base_offset munging - on IRC you suggested dropping imm_offset, so it
> > didn't appear to actually do anything. Feel free to put it back in if you
> > need it, or switch your code to not use base_offset.
> >
> > But we're using regs_read() now rather than RA hackery, and using a register
> > with a HW_REG file instead of an IMM offset, so that should be a lot more
> > reusable.
> >
> > diff --git a/src/mesa/drivers/dri/i965/brw_defines.h b/src/mesa/drivers/dri/i965/brw_defines.h
> > index 99a3a2d..6e1cfed 100644
> > --- a/src/mesa/drivers/dri/i965/brw_defines.h
> > +++ b/src/mesa/drivers/dri/i965/brw_defines.h
> > @@ -1268,6 +1268,15 @@ enum opcode {
> > * Calculate the high 32-bits of a 32x32 multiply.
> > */
> > SHADER_OPCODE_MULH,
> > +
> > + /**
> > + * A MOV that uses VxH indirect addressing.
> > + *
> > + * Source 0: A register to start from (HW_REG).
> > + * Source 1: An indirect offset (in bytes, UD GRF).
> > + * Source 2: The maximum value of the indirect offset (in bytes, UD IMM).
> > + */
> > + SHADER_OPCODE_MOV_INDIRECT,
> > };
> >
> > enum brw_urb_write_flags {
> > diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
> > index be712e5..bf8a4a6 100644
> > --- a/src/mesa/drivers/dri/i965/brw_fs.cpp
> > +++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
> > @@ -841,6 +841,30 @@ fs_inst::regs_read(int arg) const
> > case SHADER_OPCODE_BARRIER:
> > return 1;
> >
> > + case SHADER_OPCODE_MOV_INDIRECT:
> > + if (arg == 0) {
> > + assert(src[2].file == IMM);
> > + unsigned max_indirect = src[2].fixed_hw_reg.dw1.ud;
> > +
> > + if (src[0].file == HW_REG) {
> > + assert(src[0].file == HW_REG);
> > +
> > + unsigned regs = DIV_ROUND_UP(max_indirect, REG_SIZE);
> > +
> > + /* If the start of the region is not register aligned, then
> > + * we only read part of the register at the beginning, but
> > + * overlap into another register at the end. So add 1.
> > + */
> > + if (src[0].fixed_hw_reg.subnr)
> > + regs++;
>
> This isn't quite correct. It's actually more complicated based on the
> register stride, the actual subnr, and the actual (not rounded) size
> of max_indirect. However, this will give you enough registers and,
> since we're dealing with HW_REG, that's good enough.
Was your code more correct? I'm happy to change it to be more accurate.
I suppose this could be pretty off if the strides/types are small.
Do you have an example that's wrong?
> > +
> > + return regs;
> > + } else {
> > + assert(!"Invalid register file");
> > + }
> > + }
> > + break;
> > +
> > default:
> > if (is_tex() && arg == 0 && src[0].file == GRF)
> > return mlen;
> > diff --git a/src/mesa/drivers/dri/i965/brw_fs.h b/src/mesa/drivers/dri/i965/brw_fs.h
> > index 8a93b56..c599cde 100644
> > --- a/src/mesa/drivers/dri/i965/brw_fs.h
> > +++ b/src/mesa/drivers/dri/i965/brw_fs.h
> > @@ -526,6 +526,11 @@ private:
> > struct brw_reg offset,
> > struct brw_reg value);
> >
> > + void generate_mov_indirect(fs_inst *inst,
> > + struct brw_reg dst,
> > + struct brw_reg reg,
> > + struct brw_reg indirect_byte_offset);
> > +
> > bool patch_discard_jumps_to_fb_writes();
> >
> > const struct brw_compiler *compiler;
> > diff --git a/src/mesa/drivers/dri/i965/brw_fs_cse.cpp b/src/mesa/drivers/dri/i965/brw_fs_cse.cpp
> > index 3a28c8d..ffb5f87 100644
> > --- a/src/mesa/drivers/dri/i965/brw_fs_cse.cpp
> > +++ b/src/mesa/drivers/dri/i965/brw_fs_cse.cpp
> > @@ -78,6 +78,7 @@ is_expression(const fs_visitor *v, const fs_inst *const inst)
> > case FS_OPCODE_LINTERP:
> > case SHADER_OPCODE_FIND_LIVE_CHANNEL:
> > case SHADER_OPCODE_BROADCAST:
> > + case SHADER_OPCODE_MOV_INDIRECT:
> > return true;
> > case SHADER_OPCODE_RCP:
> > case SHADER_OPCODE_RSQ:
> > diff --git a/src/mesa/drivers/dri/i965/brw_fs_generator.cpp b/src/mesa/drivers/dri/i965/brw_fs_generator.cpp
> > index 974219f..97a85bb 100644
> > --- a/src/mesa/drivers/dri/i965/brw_fs_generator.cpp
> > +++ b/src/mesa/drivers/dri/i965/brw_fs_generator.cpp
> > @@ -368,6 +368,36 @@ fs_generator::generate_fb_write(fs_inst *inst, struct brw_reg payload)
> > }
> >
> > void
> > +fs_generator::generate_mov_indirect(fs_inst *inst,
> > + struct brw_reg dst,
> > + struct brw_reg reg,
> > + struct brw_reg indirect_byte_offset)
> > +{
> > + assert(indirect_byte_offset.type == BRW_REGISTER_TYPE_UD);
> > + assert(indirect_byte_offset.file == BRW_GENERAL_REGISTER_FILE);
> > +
> > + unsigned imm_byte_offset = reg.nr * REG_SIZE + reg.subnr;
> > +
> > + /* We use VxH indirect addressing, clobbering a0.0 through a0.7. */
> > + struct brw_reg addr = vec8(brw_address_reg(0));
> > +
> > + /* The destination stride of an instruction (in bytes) must be greater
> > + * than or equal to the size of the rest of the instruction. Since the
> > + * address register is of type UW, we can't use a D-type instruction.
> > + * In order to get around this, re re-type to UW and use a stride.
> > + */
> > + indirect_byte_offset =
> > + retype(spread(indirect_byte_offset, 2), BRW_REGISTER_TYPE_UW);
> > +
> > + /* Prior to Broadwell, there are only 8 address registers. */
> > + assert(inst->exec_size == 8 || devinfo->gen >= 8);
> > +
> > + brw_MOV(p, addr, indirect_byte_offset);
> > + brw_inst_set_mask_control(devinfo, brw_last_inst, BRW_MASK_DISABLE);
>
> Why are we disabling the mask?
I suppose it's not required, as none of the unset values will actually
be used by the next instruction. I can drop that.
> > + brw_MOV(p, dst, retype(brw_VxH_indirect(0, imm_byte_offset), dst.type));
> > +}
> > +
> > +void
> > fs_generator::generate_urb_read(fs_inst *inst,
> > struct brw_reg dst,
> > struct brw_reg header)
> > @@ -2070,6 +2100,10 @@ fs_generator::generate_code(const cfg_t *cfg, int dispatch_width)
> > fill_count++;
> > break;
> >
> > + case SHADER_OPCODE_MOV_INDIRECT:
> > + generate_mov_indirect(inst, dst, src[0], src[1]);
> > + break;
> > +
> > case SHADER_OPCODE_URB_READ_SIMD8:
> > generate_urb_read(inst, dst, src[0]);
> > break;
> > diff --git a/src/mesa/drivers/dri/i965/brw_shader.cpp b/src/mesa/drivers/dri/i965/brw_shader.cpp
> > index a6b57c3..9550a62 100644
> > --- a/src/mesa/drivers/dri/i965/brw_shader.cpp
> > +++ b/src/mesa/drivers/dri/i965/brw_shader.cpp
> > @@ -552,6 +552,8 @@ brw_instruction_name(enum opcode op)
> > return "barrier";
> > case SHADER_OPCODE_MULH:
> > return "mulh";
> > + case SHADER_OPCODE_MOV_INDIRECT:
> > + return "mov_indirect";
> > }
> >
> > unreachable("not reached");
> > --
> > 2.6.2
> >
> > _______________________________________________
> > mesa-dev mailing list
> > mesa-dev at lists.freedesktop.org
> > http://lists.freedesktop.org/mailman/listinfo/mesa-dev
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