[Mesa-dev] [PATCH 1/2] gallium/tgsi: add support for DEMOTE and READ_HELPER opcodes

[Ilia Mirkin]

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 at alum.mit.edu>
---
 .../auxiliary/tgsi/tgsi_info_opcodes.h        |  4 ++--
 src/gallium/docs/source/tgsi.rst              | 21 +++++++++++++++++++
 src/gallium/include/pipe/p_shader_tokens.h    |  4 ++--
 src/mesa/state_tracker/st_glsl_to_tgsi.cpp    |  7 +++++--
 4 files changed, 30 insertions(+), 6 deletions(-)

diff --git a/src/gallium/auxiliary/tgsi/tgsi_info_opcodes.h b/src/gallium/auxiliary/tgsi/tgsi_info_opcodes.h
index 0b9b264bc53..7aecda44b82 100644
--- a/src/gallium/auxiliary/tgsi/tgsi_info_opcodes.h
+++ b/src/gallium/auxiliary/tgsi/tgsi_info_opcodes.h
@@ -29,11 +29,11 @@ OPCODE(1, 1, COMP, ROUND)
 OPCODE(1, 1, REPL, EX2)
 OPCODE(1, 1, REPL, LG2)
 OPCODE(1, 2, REPL, POW)
-OPCODE_GAP(31) /* removed */
+OPCODE(0, 0, NONE, DEMOTE)
 OPCODE(1, 1, COMP, U2I64)
 OPCODE(1, 0, OTHR, CLOCK)
 OPCODE(1, 1, COMP, I2I64)
-OPCODE_GAP(35) /* removed */
+OPCODE(1, 0, COMP, READ_HELPER)
 OPCODE(1, 1, REPL, COS)
 OPCODE(1, 1, COMP, DDX)
 OPCODE(1, 1, COMP, DDY)
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
diff --git a/src/gallium/include/pipe/p_shader_tokens.h b/src/gallium/include/pipe/p_shader_tokens.h
index b30a257df2f..5770eba0837 100644
--- a/src/gallium/include/pipe/p_shader_tokens.h
+++ b/src/gallium/include/pipe/p_shader_tokens.h
@@ -376,11 +376,11 @@ enum tgsi_opcode {
    TGSI_OPCODE_EX2                = 28,
    TGSI_OPCODE_LG2                = 29,
    TGSI_OPCODE_POW                = 30,
-   /* gap */
+   TGSI_OPCODE_DEMOTE             = 31,
    TGSI_OPCODE_U2I64              = 32,
    TGSI_OPCODE_CLOCK              = 33,
    TGSI_OPCODE_I2I64              = 34,
-   /* gap */
+   TGSI_OPCODE_READ_HELPER        = 35,
    TGSI_OPCODE_COS                = 36,
    TGSI_OPCODE_DDX                = 37,
    TGSI_OPCODE_DDY                = 38,
diff --git a/src/mesa/state_tracker/st_glsl_to_tgsi.cpp b/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
index 799c161cfaf..be582f5f01c 100644
--- a/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
+++ b/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
@@ -4107,6 +4107,10 @@ glsl_to_tgsi_visitor::visit(ir_call *ir)
       visit_generic_intrinsic(ir, TGSI_OPCODE_READ_INVOC);
       return;
 
+   case ir_intrinsic_helper_invocation:
+      visit_generic_intrinsic(ir, TGSI_OPCODE_READ_HELPER);
+      return;
+
    case ir_intrinsic_invalid:
    case ir_intrinsic_generic_load:
    case ir_intrinsic_generic_store:
@@ -4120,7 +4124,6 @@ glsl_to_tgsi_visitor::visit(ir_call *ir)
    case ir_intrinsic_generic_atomic_comp_swap:
    case ir_intrinsic_begin_invocation_interlock:
    case ir_intrinsic_end_invocation_interlock:
-   case ir_intrinsic_helper_invocation:
       unreachable("Invalid intrinsic");
    }
 }
@@ -4631,7 +4634,7 @@ glsl_to_tgsi_visitor::visit(ir_discard *ir)
 void
 glsl_to_tgsi_visitor::visit(ir_demote *ir)
 {
-   assert(!"demote statement unsupported");
+   emit_asm(ir, TGSI_OPCODE_DEMOTE);
 }
 
 void
-- 
2.21.0