From page 76 (page 80 of the PDF) of the GLSL 4.60 v.5 spec:
" No aliasing in output buffers is allowed: It is a compile-time or
link-time error to specify variables with overlapping transform
feedback offsets."
Currently, this is expected to fail, but it succeeds:
"
...
layout (xfb_offset = 0) out vec2 a;
layout (xfb_offset = 0) out vec4 b;
...
"
v2: use a data structure to track the used components instead of a
nested loop (Ilia).
Cc: Timothy Arceri <tarc...@itsqueeze.com>
Cc: Ilia Mirkin <imir...@alum.mit.edu>
Signed-off-by: Andres Gomez <ago...@igalia.com>
---
src/compiler/glsl/link_varyings.cpp | 89 ++++++++++++++++++++++-------
src/mesa/main/mtypes.h | 3 +
2 files changed, 70 insertions(+), 22 deletions(-)
diff --git a/src/compiler/glsl/link_varyings.cpp
b/src/compiler/glsl/link_varyings.cpp
index 8c7d6c14c8f..95e9ae895d2 100644
--- a/src/compiler/glsl/link_varyings.cpp
+++ b/src/compiler/glsl/link_varyings.cpp
@@ -1173,6 +1173,73 @@ tfeedback_decl::store(struct gl_context *ctx, struct
gl_shader_program *prog,
unsigned location = this->location;
unsigned location_frac = this->location_frac;
unsigned num_components = this->num_components();
+
+ /* From GL_EXT_transform_feedback:
+ * A program will fail to link if:
+ *
+ * * the total number of components to capture is greater than the
+ * constant MAX_TRANSFORM_FEEDBACK_INTERLEAVED_COMPONENTS_EXT and
+ * the buffer mode is INTERLEAVED_ATTRIBS_EXT.
+ *
+ * From GL_ARB_enhanced_layouts:
+ *
+ * "The resulting stride (implicit or explicit) must be less than or
+ * equal to the implementation-dependent constant
+ * gl_MaxTransformFeedbackInterleavedComponents."
+ */
+ if ((prog->TransformFeedback.BufferMode == GL_INTERLEAVED_ATTRIBS ||
+ has_xfb_qualifiers) &&
+ xfb_offset + num_components >
+ ctx->Const.MaxTransformFeedbackInterleavedComponents) {
+ linker_error(prog,
+ "The MAX_TRANSFORM_FEEDBACK_INTERLEAVED_COMPONENTS "
+ "limit has been exceeded.");
+ return false;
+ }
+
+ {
+ /* From the OpenGL 4.60.5 spec, section 4.4.2. Output Layout
+ * Qualifiers, Page 76, (Transform Feedback Layout Qualifiers):
+ *
+ * "No aliasing in output buffers is allowed: It is a compile-time or
+ * link-time error to specify variables with overlapping transform
+ * feedback offsets."
+ */
+ const unsigned max_components =
+ ctx->Const.MaxTransformFeedbackInterleavedComponents;
+ const unsigned first_component = xfb_offset;
+ const unsigned last_component = xfb_offset + num_components - 1;
+ const unsigned start_word = BITSET_BITWORD(first_component);
+ const unsigned end_word = BITSET_BITWORD(last_component);
+ assert(last_component < max_components);
+
+ if (!info->Buffers[buffer].UsedComponents) {
+ info->Buffers[buffer].UsedComponents =
+ rzalloc_array(info, BITSET_WORD, BITSET_WORDS(max_components));
+ }
+ BITSET_WORD *used = info->Buffers[buffer].UsedComponents;
+
+ for (unsigned word = start_word; word <= end_word; word++) {
+ unsigned start_range = 0;
+ unsigned end_range = BITSET_WORDBITS - 1;
+
+ if (word == start_word)
+ start_range = first_component % BITSET_WORDBITS;
+
+ if (word == end_word)
+ end_range = last_component % BITSET_WORDBITS;
+
+ if (used[word] & BITSET_RANGE(start_range, end_range)) {
+ linker_error(prog,
+ "variable '%s', xfb_offset (%d) "
+ "is causing aliasing.",
+ this->orig_name, xfb_offset * 4);
+ return false;
+ }
+ used[word] |= BITSET_RANGE(start_range, end_range);
+ }
+ }
+
while (num_components > 0) {
unsigned output_size = MIN2(num_components, 4 - location_frac);
assert((info->NumOutputs == 0 && max_outputs == 0) ||
@@ -1223,28 +1290,6 @@ tfeedback_decl::store(struct gl_context *ctx, struct
gl_shader_program *prog,
info->Buffers[buffer].Stride = xfb_offset;
}
- /* From GL_EXT_transform_feedback:
- * A program will fail to link if:
- *
- * * the total number of components to capture is greater than
- * the constant MAX_TRANSFORM_FEEDBACK_INTERLEAVED_COMPONENTS_EXT
- * and the buffer mode is INTERLEAVED_ATTRIBS_EXT.
- *
- * From GL_ARB_enhanced_layouts:
- *
- * "The resulting stride (implicit or explicit) must be less than or
- * equal to the implementation-dependent constant
- * gl_MaxTransformFeedbackInterleavedComponents."
- */
- if ((prog->TransformFeedback.BufferMode == GL_INTERLEAVED_ATTRIBS ||
- has_xfb_qualifiers) &&
- info->Buffers[buffer].Stride >
- ctx->Const.MaxTransformFeedbackInterleavedComponents) {
- linker_error(prog, "The MAX_TRANSFORM_FEEDBACK_INTERLEAVED_COMPONENTS "
- "limit has been exceeded.");
- return false;
- }
-
store_varying:
info->Varyings[info->NumVarying].Name = ralloc_strdup(prog,
this->orig_name);
diff --git a/src/mesa/main/mtypes.h b/src/mesa/main/mtypes.h
index dda96cd2f19..a32128ec6b9 100644
--- a/src/mesa/main/mtypes.h
+++ b/src/mesa/main/mtypes.h
@@ -49,6 +49,7 @@
#include "compiler/glsl/list.h"
#include "util/simple_mtx.h"
#include "util/u_dynarray.h"
+#include "util/bitset.h"
#ifdef __cplusplus
@@ -1764,6 +1765,8 @@ struct gl_transform_feedback_buffer
uint32_t NumVaryings;
+ BITSET_WORD *UsedComponents;
+
/**
* Total number of components stored in each buffer. This may be used by
* hardware back-ends to determine the correct stride when interleaving
--
2.20.1
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