gallium/tgsi: add support for DEMOTE and READ_HELPER opcodes

This mirrors the intrinsics in the GLSL IR. One could imagine an
alternate definition where reading the semantic would account for the
READ_HELPER functionality, but that feels potentially dodgy and could be
subject to CSE unpleasantness.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>

1 files changed, 21 insertions, 0 deletions

diff --git a/src/gallium/docs/source/tgsi.rst b/src/gallium/docs/source/tgsi.rst
index 287f4b72729..d58b23f024b 100644
--- a/src/gallium/docs/source/tgsi.rst
+++ b/src/gallium/docs/source/tgsi.rst
@@ -681,6 +681,27 @@ This instruction replicates its result.
   Unconditional discard.  Allowed in fragment shaders only.
 
 
+.. opcode:: DEMOTE - Demote Invocation to a Helper
+
+  This demotes the current invocation to a helper, but continues
+  execution (while KILL may or may not terminate the
+  invocation). After this runs, all the usual helper invocation rules
+  apply about discarding buffer and render target writes. This is
+  useful for having accurate derivatives in the other invocations
+  which have not been demoted.
+
+  Allowed in fragment shaders only.
+
+
+.. opcode:: READ_HELPER - Reads Invocation Helper Status
+
+  This is identical to ``TGSI_SEMANTIC_HELPER_INVOCATION``, except
+  this will read the current value, which might change as a result of
+  a ``DEMOTE`` instruction.
+
+  Allowed in fragment shaders only.
+
+
 .. opcode:: TXB - Texture Lookup With Bias
 
   for cube map array textures and shadow cube maps, the bias value