nir: Make nir_opt_remove_phis see through moves.
I found a shader in Tales of Maj'Eyal that contains: if ssa_21 { block block_1: /* preds: block_0 */ ...instructions that prevent the select peephole... vec1 32 ssa_23 = imov ssa_4 vec1 32 ssa_24 = imov ssa_4.y vec1 32 ssa_25 = imov ssa_4.z /* succs: block_3 */ } else { block block_2: /* preds: block_0 */ vec1 32 ssa_26 = imov ssa_4 vec1 32 ssa_27 = imov ssa_4.y vec1 32 ssa_28 = imov ssa_4.z /* succs: block_3 */ } block block_3: /* preds: block_1 block_2 */ vec1 32 ssa_29 = phi block_1: ssa_23, block_2: ssa_26 vec1 32 ssa_30 = phi block_1: ssa_24, block_2: ssa_27 vec1 32 ssa_31 = phi block_1: ssa_25, block_2: ssa_28 Here, copy propagation will bail because phis cannot perform swizzles, and CSE won't do anything because there is no dominance relationship between the imovs. By making nir_opt_remove_phis handle identical moves, we can eliminate the phis and rewrite everything to use ssa_4 directly, so all the moves become dead and get eliminated. I don't think we need to check "exact" - just the alu sources. Presumably phi sources should match in their exactness. On Broadwell: total instructions in shared programs: 11639872 -> 11638535 (-0.01%) instructions in affected programs: 134222 -> 132885 (-1.00%) helped: 338 HURT: 0 v2: Fix return value to be NULL, not false (caught by Iago). Signed-off-by: Kenneth Graunke <kenneth@whitecape.org> Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
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@ -27,6 +27,26 @@
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#include "nir.h"
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static nir_alu_instr *
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get_parent_mov(nir_ssa_def *ssa)
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{
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if (ssa->parent_instr->type != nir_instr_type_alu)
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return NULL;
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nir_alu_instr *alu = nir_instr_as_alu(ssa->parent_instr);
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return (alu->op == nir_op_imov || alu->op == nir_op_fmov) ? alu : NULL;
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}
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static bool
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matching_mov(nir_alu_instr *mov1, nir_ssa_def *ssa)
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{
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if (!mov1)
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return false;
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nir_alu_instr *mov2 = get_parent_mov(ssa);
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return mov2 && nir_alu_srcs_equal(mov1, mov2, 0, 0);
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}
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/*
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* This is a pass for removing phi nodes that look like:
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* a = phi(b, b, b, ...)
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@ -54,6 +74,7 @@ remove_phis_block(nir_block *block)
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nir_phi_instr *phi = nir_instr_as_phi(instr);
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nir_ssa_def *def = NULL;
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nir_alu_instr *mov = NULL;
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bool srcs_same = true;
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nir_foreach_phi_src(src, phi) {
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@ -75,8 +96,9 @@ remove_phis_block(nir_block *block)
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if (def == NULL) {
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def = src->src.ssa;
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mov = get_parent_mov(def);
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} else {
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if (src->src.ssa != def) {
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if (src->src.ssa != def && !matching_mov(mov, src->src.ssa)) {
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srcs_same = false;
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break;
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}
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