nir: add iabs-lowering code

Microsoft's DXIL is based on LLVM, which doesn't have an integer ABS
opcode, but instead needs it lowered to NEG + MAX. We need to do this
with an option, to prevent an already existing optimization rule from
undoing this.

Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5211>

diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
index 005f7625a602047cc8c269f1a9855a6c42e3f189..aa7ff44985e98f3896242352ff23aa7a9ae223ef 100644 (file)
--- a/src/compiler/nir/nir.h
+++ b/src/compiler/nir/nir.h
@@ -3042,6 +3042,9 @@ typedef struct nir_shader_compiler_options {
    /** enables rules to lower fsign to fsub and flt */
    bool lower_fsign;
 
+   /** enables rules to lower iabs to ineg+imax */
+   bool lower_iabs;
+
    /* lower fdph to fdot4 */
    bool lower_fdph;
 

diff --git a/src/compiler/nir/nir_opt_algebraic.py b/src/compiler/nir/nir_opt_algebraic.py
index 65cff5c04eb6ff18852105d8aa2ca62fd2d2ec0e..4a2efa8252f62963e1a8b294d22ad8dcfa54b43a 100644 (file)
--- a/src/compiler/nir/nir_opt_algebraic.py
+++ b/src/compiler/nir/nir_opt_algebraic.py
@@ -543,7 +543,7 @@ optimizations.extend([
    (('fmax', a, ('fabs', a)), ('fabs', a)),
    (('imax', a, ('iabs', a)), ('iabs', a)),
    (('fmax', a, ('fneg', a)), ('fabs', a)),
-   (('imax', a, ('ineg', a)), ('iabs', a)),
+   (('imax', a, ('ineg', a)), ('iabs', a), '!options->lower_iabs'),
    (('~fmax', ('fabs', a), 0.0), ('fabs', a)),
    (('fmin', ('fmax', a, 0.0), 1.0), ('fsat', a), '!options->lower_fsat'),
    # fmax(fmin(a, 1.0), 0.0) is inexact because it returns 1.0 on NaN, while
@@ -1902,6 +1902,7 @@ late_optimizations = [
    (('iadd', 'a', ('ineg', 'b')), ('isub', 'a', 'b'), '!options->lower_sub'),
    (('fneg', a), ('fsub', 0.0, a), 'options->lower_negate'),
    (('ineg', a), ('isub', 0, a), 'options->lower_negate'),
+   (('iabs', a), ('imax', a, ('ineg', a)), 'options->lower_iabs'),
 
    # These are duplicated from the main optimizations table.  The late
    # patterns that rearrange expressions like x - .5 < 0 to x < .5 can create