From fd05620e437e4957c9408cae249517f00236cee6 Mon Sep 17 00:00:00 2001 From: Yevhenii Kolesnikov Date: Thu, 24 Dec 2020 01:16:38 +0200 Subject: [PATCH] nir/from_ssa: consider defs in sibling blocks If def a and def b are in sibling blocks, the one with higher parent_instr's index does not necessarily come after the other. Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/3712 Fixes: 943ddb945877fc8 "nir: Add a better out-of-SSA pass" Signed-off-by: Yevhenii Kolesnikov Reviewed-by: Jason Ekstrand Part-of: --- src/compiler/nir/nir_from_ssa.c | 19 ++++++++++++++++++- 1 file changed, 18 insertions(+), 1 deletion(-) diff --git a/src/compiler/nir/nir_from_ssa.c b/src/compiler/nir/nir_from_ssa.c index 3e98f317140..c624321b3d0 100644 --- a/src/compiler/nir/nir_from_ssa.c +++ b/src/compiler/nir/nir_from_ssa.c @@ -45,6 +45,15 @@ struct from_ssa_state { }; /* Returns if def @a comes after def @b. + * + * The core observation that makes the Boissinot algorithm efficient + * is that, given two properly sorted sets, we can check for + * interference in these sets via a linear walk. This is accomplished + * by doing single combined walk over union of the two sets in DFS + * order. It doesn't matter what DFS we do so long as we're + * consistent. Fortunately, the dominance algorithm we ran prior to + * this pass did such a walk and recorded the pre- and post-indices in + * the blocks. * * We treat SSA undefs as always coming before other instruction types. */ @@ -57,7 +66,15 @@ def_after(nir_ssa_def *a, nir_ssa_def *b) if (b->parent_instr->type == nir_instr_type_ssa_undef) return true; - return a->parent_instr->index > b->parent_instr->index; + /* If they're in the same block, we can rely on whichever instruction + * comes first in the block. + */ + if (a->parent_instr->block == b->parent_instr->block) + return a->parent_instr->index > b->parent_instr->index; + + /* Otherwise, if blocks are distinct, we sort them in DFS pre-order */ + return a->parent_instr->block->dom_pre_index > + b->parent_instr->block->dom_pre_index; } /* Returns true if a dominates b */