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nir/trivialize: Move decl_reg to the start of the block

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This makes it so we never find a reg_decl in between a reg_store and the def
for its value, which helps avid inserting copy movs.

Reviewed-by: Faith Ekstrand <faith.ekstrand@collabora.com>
Reviewed-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24153>
This commit is contained in:
Iago Toral Quiroga 2023-07-20 11:16:07 +02:00 • committed by Marge Bot
parent 0655bada4b
commit dff85b6163
1 changed files with 27 additions and 0 deletions
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27
src/compiler/nir/nir_trivialize_registers.c
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@ -62,6 +62,30 @@
* This pass inserts copies to ensure that all load_reg/store_reg are trivial.
*/
/*
* In order to allow for greater freedom elsewhere in the pass, move all
* reg_decl intrinsics to the top of their block. This ensures in particular
* that decl_reg intrinsics occur before the producer of the SSA value
* consumed by a store_reg whenever they're all in the same block.
*/
static void
move_reg_decls(nir_block *block)
{
nir_cursor cursor = nir_before_block(block);
nir_foreach_instr_safe(instr, block) {
if (instr->type != nir_instr_type_intrinsic)
continue;
nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
if (intr->intrinsic != nir_intrinsic_decl_reg)
continue;
nir_instr_move(cursor, instr);
cursor = nir_after_instr(instr);
}
}
/*
* Any load can be trivialized by copying immediately after the load and then
* rewriting uses of the load to read from the copy. That has no functional
@ -459,6 +483,9 @@ void
nir_trivialize_registers(nir_shader *s)
{
nir_foreach_function_impl(impl, s) {
/* All decl_reg intrinsics are in the start block. */
move_reg_decls(nir_start_block(impl));
nir_foreach_block(block, impl) {
trivialize_loads(impl, block);
trivialize_stores(impl, block);