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pan/mdg: Fix 2-const CSEL at block beginning

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mir_prev_op will point to the last instruction of the block in that case because
the block instruction list is circular. That would cause an invald
write-after-read relationship between the move we insert with the constants and
the CSEL reading them, which DCE "helpfully" optimizes out, leaving a read from
an undefined def. That ends up getting RA'd to an invalid register.

All in all, pretty bad.

Identified due to a new assert fail after the proper temp_count fix.

Affects dEQP-GLES31.functional.separate_shader.random.12.

No shader-db changes.

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Reviewed-by: Italo Nicola <italonicola@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/23769>
This commit is contained in:
Alyssa Rosenzweig 2023-06-30 16:05:58 -04:00
parent b66b122e03
commit 7da1e4c326
1 changed files with 11 additions and 2 deletions
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13
src/panfrost/midgard/midgard_compile.c
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@ -2471,8 +2471,17 @@ inline_alu_constants(compiler_context *ctx, midgard_block *block)
/* Set the source */
alu->src[1] = scratch;
/* Inject us -before- the last instruction which set r31 */
mir_insert_instruction_before(ctx, mir_prev_op(alu), ins);
/* Inject us -before- the last instruction which set r31, if
* possible.
*/
midgard_instruction *first = list_first_entry(
&block->base.instructions, midgard_instruction, link);
if (alu == first) {
mir_insert_instruction_before(ctx, alu, ins);
} else {
mir_insert_instruction_before(ctx, mir_prev_op(alu), ins);
}
}
}
}