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broadcom/compiler: disable flags optimization for loop conditions

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This is not safe because it may skip regenerating the flags for the
loop condition in the loop continue block and these flags may be
stomped in the loop body by other conditionals.

Fixes: 9909fe6ba ('broadcom/compiler: Skip bool_to_cond where possible')
Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17020>
This commit is contained in:
Iago Toral Quiroga 2022-06-10 10:46:51 +02:00 • committed by Marge Bot
parent 2b0e45b18e
commit a97f78eb14
1 changed files with 17 additions and 1 deletions
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18
src/broadcom/compiler/nir_to_vir.c
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@ -4170,7 +4170,6 @@ ntq_emit_nonuniform_loop(struct v3d_compile *c, nir_loop *loop)
static void
ntq_emit_uniform_loop(struct v3d_compile *c, nir_loop *loop)
{
c->loop_cont_block = vir_new_block(c);
c->loop_break_block = vir_new_block(c);
@ -4190,6 +4189,23 @@ ntq_emit_uniform_loop(struct v3d_compile *c, nir_loop *loop)
static void
ntq_emit_loop(struct v3d_compile *c, nir_loop *loop)
{
/* Disable flags optimization for loop conditions. The problem here is
* that we can have code like this:
*
* // block_0
* vec1 32 con ssa_9 = ine32 ssa_8, ssa_2
* loop {
* // block_1
* if ssa_9 {
*
* In this example we emit flags to compute ssa_9 and the optimization
* will skip regenerating them again for the loop condition in the
* loop continue block (block_1). However, this is not safe after the
* first iteration because the loop body can stomp the flags if it has
* any conditionals.
*/
c->flags_temp = -1;
bool was_in_control_flow = c->in_control_flow;
c->in_control_flow = true;