An untyped surface read is volatile because it might be affected by a
write.
In the ES31-CTS.compute_shader.resources-max test, two back to back
read/modify/writes of an SSBO variable looked something like this:
r1 = untyped_surface_read(ssbo_float)
r2 = r1 + 1
untyped_surface_write(ssbo_float, r2)
r3 = untyped_surface_read(ssbo_float)
r4 = r3 + 1
untyped_surface_write(ssbo_float, r4)
And after CSE, we had:
r1 = untyped_surface_read(ssbo_float)
r2 = r1 + 1
untyped_surface_write(ssbo_float, r2)
r4 = r1 + 1
untyped_surface_write(ssbo_float, r4)
Signed-off-by: Jordan Justen <jordan.l.jus...@intel.com>
---
src/mesa/drivers/dri/i965/brw_fs_cse.cpp | 3 ++-
src/mesa/drivers/dri/i965/brw_shader.cpp | 14 ++++++++++++++
src/mesa/drivers/dri/i965/brw_shader.h | 6 ++++++
3 files changed, 22 insertions(+), 1 deletion(-)
diff --git a/src/mesa/drivers/dri/i965/brw_fs_cse.cpp
b/src/mesa/drivers/dri/i965/brw_fs_cse.cpp
index c7628dc..3a28c8d 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_cse.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_cse.cpp
@@ -93,7 +93,8 @@ is_expression(const fs_visitor *v, const fs_inst *const inst)
case SHADER_OPCODE_LOAD_PAYLOAD:
return !inst->is_copy_payload(v->alloc);
default:
- return inst->is_send_from_grf() && !inst->has_side_effects();
+ return inst->is_send_from_grf() && !inst->has_side_effects() &&
+ !inst->is_volatile();
}
}
diff --git a/src/mesa/drivers/dri/i965/brw_shader.cpp
b/src/mesa/drivers/dri/i965/brw_shader.cpp
index 2324b56..be911ed 100644
--- a/src/mesa/drivers/dri/i965/brw_shader.cpp
+++ b/src/mesa/drivers/dri/i965/brw_shader.cpp
@@ -969,6 +969,20 @@ backend_instruction::has_side_effects() const
}
}
+bool
+backend_instruction::is_volatile() const
+{
+ switch (opcode) {
+ case SHADER_OPCODE_UNTYPED_SURFACE_READ:
+ case SHADER_OPCODE_UNTYPED_SURFACE_READ_LOGICAL:
+ case SHADER_OPCODE_TYPED_SURFACE_READ:
+ case SHADER_OPCODE_TYPED_SURFACE_READ_LOGICAL:
+ return true;
+ default:
+ return false;
+ }
+}
+
#ifndef NDEBUG
static bool
inst_is_in_block(const bblock_t *block, const backend_instruction *inst)
diff --git a/src/mesa/drivers/dri/i965/brw_shader.h
b/src/mesa/drivers/dri/i965/brw_shader.h
index b33b08f..35ee210 100644
--- a/src/mesa/drivers/dri/i965/brw_shader.h
+++ b/src/mesa/drivers/dri/i965/brw_shader.h
@@ -115,6 +115,12 @@ struct backend_instruction : public exec_node {
* optimize these out unless you know what you are doing.
*/
bool has_side_effects() const;
+
+ /**
+ * True if the instruction might be affected by side effects of other
+ * instructions.
+ */
+ bool is_volatile() const;
#else
struct backend_instruction {
struct exec_node link;
--
2.5.1
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