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nir: Implement optional b2f->iand lowering

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This pass is required by the Midgard compiler; our instruction set uses
NIR-style booleans (~0 for true) but lacks a dedicated b2f instruction.
Normally, this lowering pass would be implemented in a backend-specific
algebraic pass, but this conflicts with the existing iand->b2f pass in
nir_opt_algebraic.py, hanging the compiler. This patch thus makes the
existing pass optional (default on -- all other backends should remain
unaffected), adding an optional pass for lowering the opposite
direction.

v2: Defer lowering until late algebraic optimisations to allow
optimising the b2f instruction itself.

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>
This commit is contained in:
Alyssa Rosenzweig
2018-05-02 02:04:55 +00:00
committed by Christian Gmeiner
parent 8ed2cabd04
commit 5d85a0a55b
2 changed files with 7 additions and 1 deletions
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3
src/compiler/nir/nir.h
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@@ -1894,6 +1894,9 @@ typedef struct nir_shader_compiler_options {
/** enables rules to lower idiv by power-of-two: */
bool lower_idiv;
/* lower b2f to iand */
bool lower_b2f;
/* Does the native fdot instruction replicate its result for four
* components? If so, then opt_algebraic_late will turn all fdotN
* instructions into fdot_replicatedN instructions.

5
src/compiler/nir/nir_opt_algebraic.py
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@@ -321,7 +321,7 @@ optimizations = [
(('imul', ('b2i', a), ('b2i', b)), ('b2i', ('iand', a, b))),
(('fmul', ('b2f', a), ('b2f', b)), ('b2f', ('iand', a, b))),
(('fsat', ('fadd', ('b2f', a), ('b2f', b))), ('b2f', ('ior', a, b))),
(('iand', 'a@bool', 1.0), ('b2f', a)),
(('iand', 'a@bool', 1.0), ('b2f', a), '!options->lower_b2f'),
# True/False are ~0 and 0 in NIR. b2i of True is 1, and -1 is ~0 (True).
(('ineg', ('b2i@32', a)), a),
(('flt', ('fneg', ('b2f', a)), 0), a), # Generated by TGSI KILL_IF.
@@ -724,6 +724,9 @@ late_optimizations = [
# we do these late so that we don't get in the way of creating ffmas
(('fmin', ('fadd(is_used_once)', '#c', a), ('fadd(is_used_once)', '#c', b)), ('fadd', c, ('fmin', a, b))),
(('fmax', ('fadd(is_used_once)', '#c', a), ('fadd(is_used_once)', '#c', b)), ('fadd', c, ('fmax', a, b))),
# Lowered for backends without a dedicated b2f instruction
(('b2f@32', a), ('iand', a, 1.0), 'options->lower_b2f'),
]
print nir_algebraic.AlgebraicPass("nir_opt_algebraic", optimizations).render()