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nir: Make vec-to-movs handle src/dest aliasing.

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It now emits vector MOVs instead of a series of individual MOVs, which
should be useful to any vector backends.  This pushes the problem of
src/dest aliasing of channels on a scalar chip to the backend, but if
there are any vector operations in your shader then you needed to be
handling this already.

Fixes fs-swap-problem with my scalarizing patches.

v2: Rename to insert_mov(), and add a comment about what it does.
v3: Rewrite the comment.

Reviewed-by: Connor Abbott <cwabbott0@gmail.com> (v3)
This commit is contained in:
Eric Anholt 2015-01-22 13:08:59 -08:00
parent d70eb38517
commit dd4d9a4e62
1 changed files with 72 additions and 10 deletions
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82
src/glsl/nir/nir_lower_vec_to_movs.c
View file

@ -32,6 +32,57 @@
* moves with partial writes.
*/
static bool
src_matches_dest_reg(nir_dest *dest, nir_src *src)
{
if (dest->is_ssa || src->is_ssa)
return false;
return (dest->reg.reg == src->reg.reg &&
dest->reg.base_offset == src->reg.base_offset &&
!dest->reg.indirect &&
!src->reg.indirect);
}
/**
* For a given starting writemask channel and corresponding source index in
* the vec instruction, insert a MOV to the vec instruction's dest of all the
* writemask channels that get read from the same src reg.
*
* Returns the writemask of our MOV, so the parent loop calling this knows
* which ones have been processed.
*/
static unsigned
insert_mov(nir_alu_instr *vec, unsigned start_channel,
unsigned start_src_idx, void *mem_ctx)
{
unsigned src_idx = start_src_idx;
assert(src_idx < nir_op_infos[vec->op].num_inputs);
nir_alu_instr *mov = nir_alu_instr_create(mem_ctx, nir_op_imov);
nir_alu_src_copy(&mov->src[0], &vec->src[src_idx], mem_ctx);
nir_alu_dest_copy(&mov->dest, &vec->dest, mem_ctx);
mov->dest.write_mask = (1u << start_channel);
mov->src[0].swizzle[start_channel] = vec->src[src_idx].swizzle[0];
src_idx++;
for (unsigned i = start_channel + 1; i < 4; i++) {
if (!(vec->dest.write_mask & (1 << i)))
continue;
if (nir_srcs_equal(vec->src[src_idx].src, vec->src[start_src_idx].src)) {
mov->dest.write_mask |= (1 << i);
mov->src[0].swizzle[i] = vec->src[src_idx].swizzle[0];
}
src_idx++;
}
nir_instr_insert_before(&vec->instr, &mov->instr);
return mov->dest.write_mask;
}
static bool
lower_vec_to_movs_block(nir_block *block, void *mem_ctx)
{
@ -50,22 +101,33 @@ lower_vec_to_movs_block(nir_block *block, void *mem_ctx)
continue; /* The loop */
}
/* Since we insert multiple MOVs, we have to be non-SSA. */
assert(!vec->dest.dest.is_ssa);
unsigned finished_write_mask = 0;
/* First, emit a MOV for all the src channels that are in the
* destination reg, in case other values we're populating in the dest
* might overwrite them.
*/
for (unsigned i = 0, src_idx = 0; i < 4; i++) {
if (!(vec->dest.write_mask & (1 << i)))
continue;
assert(src_idx < nir_op_infos[vec->op].num_inputs);
if (src_matches_dest_reg(&vec->dest.dest, &vec->src[src_idx].src)) {
finished_write_mask |= insert_mov(vec, i, src_idx, mem_ctx);
break;
}
src_idx++;
}
nir_alu_instr *mov = nir_alu_instr_create(mem_ctx, nir_op_imov);
nir_alu_src_copy(&mov->src[0], &vec->src[src_idx], mem_ctx);
/* Now, emit MOVs for all the other src channels. */
for (unsigned i = 0, src_idx = 0; i < 4; i++) {
if (!(vec->dest.write_mask & (1 << i)))
continue;
/* We only care about the one swizzle */
mov->src[0].swizzle[i] = vec->src[src_idx].swizzle[0];
nir_alu_dest_copy(&mov->dest, &vec->dest, mem_ctx);
mov->dest.write_mask = (1u << i);
nir_instr_insert_before(&vec->instr, &mov->instr);
if (!(finished_write_mask & (1 << i)))
finished_write_mask |= insert_mov(vec, i, src_idx, mem_ctx);
src_idx++;
}