aco: don't do divergent break+discard
If the shader does: loop { if (divergent) discard else a() b() } then a()'s block will dominate b()'s block in the logical CFG, but not the linear CFG. This will cause value numbering to try to combine SLAU from a() and b(). This didn't happen with break/continue because sanitize_if() would move a() out of the branch. Using sanitize_if() to fix this doesn't look easy, because discards are not control flow instructions in NIR. No fossil-db changes. Signed-off-by: Rhys Perry <pendingchaos02@gmail.com> Reviewed-by: Daniel Schürmann <daniel@schuermann.dev> Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7216>
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@ -5263,8 +5263,7 @@ void visit_discard(isel_context* ctx, nir_intrinsic_instr *instr)
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bool divergent = ctx->cf_info.parent_if.is_divergent ||
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ctx->cf_info.parent_loop.has_divergent_continue;
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if (ctx->block->loop_nest_depth &&
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((nir_instr_is_last(&instr->instr) && !divergent) || divergent)) {
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if (ctx->block->loop_nest_depth && (nir_instr_is_last(&instr->instr) && !divergent)) {
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/* we handle discards the same way as jump instructions */
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append_logical_end(ctx->block);
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@ -5272,39 +5271,12 @@ void visit_discard(isel_context* ctx, nir_intrinsic_instr *instr)
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Block *linear_target = ctx->cf_info.parent_loop.exit;
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ctx->block->kind |= block_kind_discard;
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if (!divergent) {
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/* uniform discard - loop ends here */
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assert(nir_instr_is_last(&instr->instr));
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ctx->block->kind |= block_kind_uniform;
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ctx->cf_info.has_branch = true;
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bld.branch(aco_opcode::p_branch, bld.hint_vcc(bld.def(s2)));
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add_linear_edge(ctx->block->index, linear_target);
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return;
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}
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/* we add a break right behind the discard() instructions */
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ctx->block->kind |= block_kind_break;
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unsigned idx = ctx->block->index;
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ctx->cf_info.parent_loop.has_divergent_branch = true;
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ctx->cf_info.nir_to_aco[instr->instr.block->index] = idx;
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/* remove critical edges from linear CFG */
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/* uniform discard - loop ends here */
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assert(nir_instr_is_last(&instr->instr));
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ctx->block->kind |= block_kind_uniform;
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ctx->cf_info.has_branch = true;
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bld.branch(aco_opcode::p_branch, bld.hint_vcc(bld.def(s2)));
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Block* break_block = ctx->program->create_and_insert_block();
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break_block->loop_nest_depth = ctx->cf_info.loop_nest_depth;
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break_block->kind |= block_kind_uniform;
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add_linear_edge(idx, break_block);
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add_linear_edge(break_block->index, linear_target);
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bld.reset(break_block);
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bld.branch(aco_opcode::p_branch, bld.hint_vcc(bld.def(s2)));
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Block* continue_block = ctx->program->create_and_insert_block();
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continue_block->loop_nest_depth = ctx->cf_info.loop_nest_depth;
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add_linear_edge(idx, continue_block);
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append_logical_start(continue_block);
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ctx->block = continue_block;
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add_linear_edge(ctx->block->index, linear_target);
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return;
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}
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