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nir: Correctly constant fold fsign(NaN) and fsign(-0) 

GLSL and SPIR-V GLSL.std.450 don't have any requirements for fsign(NaN),
and both only require that FSign(-0.0) == 0.0.  OpenCL, on the other
hand, requires sign(-0.0) be exactly -0.0.  It also requires that
sign(NaN) be exactly 0.0.

In practice, this change is difficult to test.  Our GLSL frontend
already constant folds sign(NaN) to 0.0 before even getting to NIR.  As
far as I can tell, glslang does the same.  I don't have a good way to
run an OpenCL SPIR-V test.  Maybe SPIR-V GLSL.std.450 assembly?

No shader-db or fossil-db changes on any Intel platform.

Acked-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6358>
This commit is contained in:
Ian Romanick 2020-02-18 12:34:15 -08:00 committed by Marge Bot
parent fe3c518277
commit 71961c73a9
1 changed files with 4 additions and 4 deletions
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8
src/compiler/nir/nir_opcodes.py
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@ -208,11 +208,11 @@ unop("inot", tint, "~src0") # invert every bit of the integer
# number, and the result is not +0.0, the result should definitely **not** be
# NaN.
#
# fsign(NaN) = (False ? 0.0 : (False ? 1.0 : -1.0) = -1.0. This is allowed by
# the spec, but it is not the preferred value.
# The values returned for constant folding match the behavior required by
# OpenCL.
unop("fsign", tfloat, ("bit_size == 64 ? " +
"((src0 == 0.0) ? 0.0 : ((src0 > 0.0) ? 1.0 : -1.0)) : " +
"((src0 == 0.0f) ? 0.0f : ((src0 > 0.0f) ? 1.0f : -1.0f))"))
"(isnan(src0) ? 0.0 : ((src0 == 0.0 ) ? src0 : (src0 > 0.0 ) ? 1.0 : -1.0 )) : " +
"(isnan(src0) ? 0.0f : ((src0 == 0.0f) ? src0 : (src0 > 0.0f) ? 1.0f : -1.0f))"))
unop("isign", tint, "(src0 == 0) ? 0 : ((src0 > 0) ? 1 : -1)")
unop("iabs", tint, "(src0 < 0) ? -src0 : src0")
unop("fabs", tfloat, "fabs(src0)")