Mesa (master): nir: Add a comment about how intrinsic definitions work.

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Module: Mesa
Branch: master
Commit: b88ef3bd76a1fad3c2a99ea19df62f7be8c57961
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=b88ef3bd76a1fad3c2a99ea19df62f7be8c57961

Author: Eric Anholt <eric at anholt.net>
Date:   Thu Apr 11 09:49:13 2019 -0700

nir: Add a comment about how intrinsic definitions work.

I was thinking about a refactor, and needed to read this first.

Reviewed-by: Jason Ekstrand <jason at jlekstrand.net>

---

 src/compiler/nir/nir_intrinsics.py | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/src/compiler/nir/nir_intrinsics.py b/src/compiler/nir/nir_intrinsics.py
index 1b4fcf9f98b..9b3f480f7af 100644
--- a/src/compiler/nir/nir_intrinsics.py
+++ b/src/compiler/nir/nir_intrinsics.py
@@ -128,6 +128,17 @@ CAN_REORDER   = "NIR_INTRINSIC_CAN_REORDER"
 
 INTR_OPCODES = {}
 
+# Defines a new NIR intrinsic.  By default, the intrinsic will have no sources
+# and no destination.
+#
+# You can set dest_comp=n to enable a destination for the intrinsic, in which
+# case it will have that many components, or =0 for "as many components as the
+# NIR destination value."
+#
+# Set src_comp=n to enable sources for the intruction.  It can be an array of
+# component counts, or (for convenience) a scalar component count if there's
+# only one source.  If a component count is 0, it will be as many components as
+# the intrinsic has based on the dest_comp.
 def intrinsic(name, src_comp=[], dest_comp=-1, indices=[],
               flags=[], sysval=False, bit_sizes=[]):
     assert name not in INTR_OPCODES