No Shader-db changes.
Cc: mesa-sta...@lists.freedesktop.org
---
src/intel/compiler/brw_fs_live_variables.cpp | 55 ++++++++++++++++++++++++++++
1 file changed, 55 insertions(+)
diff --git a/src/intel/compiler/brw_fs_live_variables.cpp
b/src/intel/compiler/brw_fs_live_variables.cpp
index c449672..380060d 100644
--- a/src/intel/compiler/brw_fs_live_variables.cpp
+++ b/src/intel/compiler/brw_fs_live_variables.cpp
@@ -223,6 +223,61 @@ fs_live_variables::compute_start_end()
}
}
}
+
+ /* Due to the explicit way the SIMD data is handled on GEN, we need to be a
+ * bit more careful with live ranges and loops. Consider the following
+ * example:
+ *
+ * vec4 color2;
+ * while (1) {
+ * vec4 color = texture();
+ * if (...) {
+ * color2 = color * 2;
+ * break;
+ * }
+ * }
+ * gl_FragColor = color2;
+ *
+ * In this case, the definition of color2 dominates the use because the
+ * loop only has the one exit. This means that the live range interval for
+ * color2 goes from the statement in the if to it's use below the loop.
+ * Now suppose that the texture operation has a header register that gets
+ * assigned one of the registers used for color2. If the loop condition is
+ * non-uniform and some of the threads will take the and others will
+ * continue. In this case, the next pass through the loop, the WE_all
+ * setup of the header register will stomp the disabled channels of color2
+ * and corrupt the value.
+ *
+ * This same problem can occur if you have a mix of 64, 32, and 16-bit
+ * registers because the channels do not line up or if you have a SIMD16
+ * program and the first half of one value overlaps the second half of the
+ * other.
+ *
+ * To solve this problem, we take any VGRFs whose live ranges cross the
+ * while instruction of a loop and extend their live ranges to the top of
+ * the loop. This more accurately models the hardware because the value in
+ * the VGRF needs to be carried through subsequent loop iterations in order
+ * to remain valid when we finally do break.
+ */
+ foreach_block (block, cfg) {
+ if (block->end()->opcode != BRW_OPCODE_WHILE)
+ continue;
+
+ /* This is a WHILE instrution. Find the DO block. */
+ bblock_t *do_block = NULL;
+ foreach_list_typed(bblock_link, child_link, link, &block->children) {
+ if (child_link->block->start_ip < block->end_ip) {
+ assert(do_block == NULL);
+ do_block = child_link->block;
+ }
+ }
+ assert(do_block);
+
+ for (int i = 0; i < num_vars; i++) {
+ if (start[i] < block->end_ip && end[i] > block->end_ip)
+ start[i] = MIN2(start[i], do_block->start_ip);
+ }
+ }
}
fs_live_variables::fs_live_variables(fs_visitor *v, const cfg_t *cfg)
--
2.5.0.400.gff86faf
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