gallium: add PIPE_CAP_TGSI_CAN_READ_OUTPUTS

Drivers that support this benefit by saving one lowering pass in the
GLSL-to-TGSI conversion.

radeonsi already supports this because all outputs are stored in temporary
variables before the export (except for TCS outputs, which have always
been readable in TGSI anyway due to their special semantics).

Reviewed-by: Marek Olšák <marek.olsak@amd.com>

src/gallium/docs/source/screen.rst

@@ -364,6 +364,8 @@ The integer capabilities:
 * ``PIPE_CAP_STREAM_OUTPUT_INTERLEAVE_BUFFERS``: Whether interleaved stream
   output mode is able to interleave across buffers. This is required for
   ARB_transform_feedback3.
+* ``PIPE_CAP_TGSI_CAN_READ_OUTPUTS``: Whether every TGSI shader stage can read
+  from the output file.
 
 
 .. _pipe_capf:

src/gallium/drivers/freedreno/freedreno_screen.c

@@ -288,6 +288,7 @@ fd_screen_get_param(struct pipe_screen *pscreen, enum pipe_cap param)
 	case PIPE_CAP_POLYGON_OFFSET_UNITS_UNSCALED:
 	case PIPE_CAP_VIEWPORT_SUBPIXEL_BITS:
 	case PIPE_CAP_TGSI_ARRAY_COMPONENTS:
+	case PIPE_CAP_TGSI_CAN_READ_OUTPUTS:
 		return 0;
 
 	case PIPE_CAP_MAX_VIEWPORTS:

src/gallium/drivers/i915/i915_screen.c

@@ -294,6 +294,7 @@ i915_get_param(struct pipe_screen *screen, enum pipe_cap cap)
    case PIPE_CAP_TGSI_FS_FINE_DERIVATIVE:
    case PIPE_CAP_SAMPLER_VIEW_TARGET:
    case PIPE_CAP_VIEWPORT_SUBPIXEL_BITS:
+   case PIPE_CAP_TGSI_CAN_READ_OUTPUTS:
       return 0;
 
    case PIPE_CAP_MAX_VIEWPORTS:

src/gallium/drivers/ilo/ilo_screen.c

@@ -517,6 +517,7 @@ ilo_get_param(struct pipe_screen *screen, enum pipe_cap param)
    case PIPE_CAP_POLYGON_OFFSET_UNITS_UNSCALED:
    case PIPE_CAP_VIEWPORT_SUBPIXEL_BITS:
    case PIPE_CAP_TGSI_ARRAY_COMPONENTS:
+   case PIPE_CAP_TGSI_CAN_READ_OUTPUTS:
       return 0;
 
    case PIPE_CAP_VENDOR_ID:

src/gallium/drivers/llvmpipe/lp_screen.c

@@ -338,6 +338,7 @@ llvmpipe_get_param(struct pipe_screen *screen, enum pipe_cap param)
    case PIPE_CAP_MAX_WINDOW_RECTANGLES:
    case PIPE_CAP_POLYGON_OFFSET_UNITS_UNSCALED:
    case PIPE_CAP_VIEWPORT_SUBPIXEL_BITS:
+   case PIPE_CAP_TGSI_CAN_READ_OUTPUTS:
       return 0;
    }
    /* should only get here on unhandled cases */

src/gallium/drivers/nouveau/nv30/nv30_screen.c

@@ -203,6 +203,7 @@ nv30_screen_get_param(struct pipe_screen *pscreen, enum pipe_cap param)
    case PIPE_CAP_VIEWPORT_SUBPIXEL_BITS:
    case PIPE_CAP_MIXED_COLOR_DEPTH_BITS:
    case PIPE_CAP_TGSI_ARRAY_COMPONENTS:
+   case PIPE_CAP_TGSI_CAN_READ_OUTPUTS:
       return 0;
 
    case PIPE_CAP_VENDOR_ID:

src/gallium/drivers/nouveau/nv50/nv50_screen.c

@@ -255,6 +255,7 @@ nv50_screen_get_param(struct pipe_screen *pscreen, enum pipe_cap param)
    case PIPE_CAP_POLYGON_OFFSET_UNITS_UNSCALED:
    case PIPE_CAP_VIEWPORT_SUBPIXEL_BITS:
    case PIPE_CAP_STREAM_OUTPUT_INTERLEAVE_BUFFERS:
+   case PIPE_CAP_TGSI_CAN_READ_OUTPUTS:
       return 0;
 
    case PIPE_CAP_VENDOR_ID:

src/gallium/drivers/nouveau/nvc0/nvc0_screen.c

@@ -274,6 +274,7 @@ nvc0_screen_get_param(struct pipe_screen *pscreen, enum pipe_cap param)
    case PIPE_CAP_PCI_DEVICE:
    case PIPE_CAP_PCI_FUNCTION:
    case PIPE_CAP_VIEWPORT_SUBPIXEL_BITS:
+   case PIPE_CAP_TGSI_CAN_READ_OUTPUTS:
       return 0;
 
    case PIPE_CAP_VENDOR_ID:

src/gallium/drivers/r300/r300_screen.c

@@ -225,6 +225,7 @@ static int r300_get_param(struct pipe_screen* pscreen, enum pipe_cap param)
         case PIPE_CAP_POLYGON_OFFSET_UNITS_UNSCALED:
         case PIPE_CAP_VIEWPORT_SUBPIXEL_BITS:
         case PIPE_CAP_TGSI_ARRAY_COMPONENTS:
+        case PIPE_CAP_TGSI_CAN_READ_OUTPUTS:
             return 0;
 
         /* SWTCL-only features. */

src/gallium/drivers/r600/r600_pipe.c

@@ -374,6 +374,7 @@ static int r600_get_param(struct pipe_screen* pscreen, enum pipe_cap param)
 	case PIPE_CAP_TGSI_VOTE:
 	case PIPE_CAP_MAX_WINDOW_RECTANGLES:
 	case PIPE_CAP_TGSI_ARRAY_COMPONENTS:
+	case PIPE_CAP_TGSI_CAN_READ_OUTPUTS:
 		return 0;
 
 	case PIPE_CAP_MAX_SHADER_PATCH_VARYINGS:

src/gallium/drivers/radeonsi/si_pipe.c

@@ -409,6 +409,7 @@ static int si_get_param(struct pipe_screen* pscreen, enum pipe_cap param)
 	case PIPE_CAP_CLEAR_TEXTURE:
 	case PIPE_CAP_CULL_DISTANCE:
 	case PIPE_CAP_TGSI_ARRAY_COMPONENTS:
+	case PIPE_CAP_TGSI_CAN_READ_OUTPUTS:
 		return 1;
 
 	case PIPE_CAP_RESOURCE_FROM_USER_MEMORY:

src/gallium/drivers/softpipe/sp_screen.c

@@ -288,6 +288,7 @@ softpipe_get_param(struct pipe_screen *screen, enum pipe_cap param)
    case PIPE_CAP_MAX_WINDOW_RECTANGLES:
    case PIPE_CAP_POLYGON_OFFSET_UNITS_UNSCALED:
    case PIPE_CAP_VIEWPORT_SUBPIXEL_BITS:
+   case PIPE_CAP_TGSI_CAN_READ_OUTPUTS:
       return 0;
    case PIPE_CAP_SHADER_BUFFER_OFFSET_ALIGNMENT:
       return 4;

src/gallium/drivers/svga/svga_screen.c

@@ -419,6 +419,7 @@ svga_get_param(struct pipe_screen *screen, enum pipe_cap param)
    case PIPE_CAP_POLYGON_OFFSET_UNITS_UNSCALED:
    case PIPE_CAP_VIEWPORT_SUBPIXEL_BITS:
    case PIPE_CAP_TGSI_ARRAY_COMPONENTS:
+   case PIPE_CAP_TGSI_CAN_READ_OUTPUTS:
       return 0;
    }
 

src/gallium/drivers/swr/swr_screen.cpp

@@ -311,6 +311,7 @@ swr_get_param(struct pipe_screen *screen, enum pipe_cap param)
    case PIPE_CAP_POLYGON_OFFSET_UNITS_UNSCALED:
    case PIPE_CAP_VIEWPORT_SUBPIXEL_BITS:
    case PIPE_CAP_TGSI_ARRAY_COMPONENTS:
+   case PIPE_CAP_TGSI_CAN_READ_OUTPUTS:
       return 0;
 
    case PIPE_CAP_VENDOR_ID:

src/gallium/drivers/vc4/vc4_screen.c

@@ -239,6 +239,7 @@ vc4_screen_get_param(struct pipe_screen *pscreen, enum pipe_cap param)
         case PIPE_CAP_POLYGON_OFFSET_UNITS_UNSCALED:
         case PIPE_CAP_VIEWPORT_SUBPIXEL_BITS:
         case PIPE_CAP_TGSI_ARRAY_COMPONENTS:
+        case PIPE_CAP_TGSI_CAN_READ_OUTPUTS:
                 return 0;
 
                 /* Stream output. */

src/gallium/drivers/virgl/virgl_screen.c

@@ -250,6 +250,7 @@ virgl_get_param(struct pipe_screen *screen, enum pipe_cap param)
    case PIPE_CAP_POLYGON_OFFSET_UNITS_UNSCALED:
    case PIPE_CAP_VIEWPORT_SUBPIXEL_BITS:
    case PIPE_CAP_TGSI_ARRAY_COMPONENTS:
+   case PIPE_CAP_TGSI_CAN_READ_OUTPUTS:
       return 0;
    case PIPE_CAP_VENDOR_ID:
       return 0x1af4;

src/gallium/include/pipe/p_defines.h

@@ -740,6 +740,7 @@ enum pipe_cap
    PIPE_CAP_MIXED_COLOR_DEPTH_BITS,
    PIPE_CAP_TGSI_ARRAY_COMPONENTS,
    PIPE_CAP_STREAM_OUTPUT_INTERLEAVE_BUFFERS,
+   PIPE_CAP_TGSI_CAN_READ_OUTPUTS,
 };
 
 #define PIPE_QUIRK_TEXTURE_BORDER_COLOR_SWIZZLE_NV50 (1 << 0)