---
src/intel/compiler/brw_nir_analyze_ubo_ranges.c | 28 ++++++++++++++++++++++++-
1 file changed, 27 insertions(+), 1 deletion(-)
diff --git a/src/intel/compiler/brw_nir_analyze_ubo_ranges.c
b/src/intel/compiler/brw_nir_analyze_ubo_ranges.c
index 3535e67758c..b365728e77b 100644
--- a/src/intel/compiler/brw_nir_analyze_ubo_ranges.c
+++ b/src/intel/compiler/brw_nir_analyze_ubo_ranges.c
@@ -83,6 +83,10 @@ cmp_ubo_range_entry(const void *va, const void *vb)
struct ubo_block_info
{
+ /* Each bit in the offsets bitfield represents a 32-byte section of data.
+ * If it's set to one, there is interesting UBO data at that offset. If
+ * not, there's a "hole" - padding between data - or just nothing at all.
+ */
uint64_t offsets;
uint8_t uses[64];
};
@@ -189,7 +193,7 @@ brw_nir_analyze_ubo_ranges(const struct brw_compiler
*compiler,
}
}
- /* Find ranges. */
+ /* Find ranges: a block, starting 32-byte offset, and length. */
struct util_dynarray ranges;
util_dynarray_init(&ranges, mem_ctx);
@@ -199,13 +203,34 @@ brw_nir_analyze_ubo_ranges(const struct brw_compiler
*compiler,
const struct ubo_block_info *info = entry->data;
uint64_t offsets = info->offsets;
+ /* Walk through the offsets bitfield, finding contiguous regions of
+ * set bits:
+ *
+ * 0000000001111111111111000000000000111111111111110000000011111100
+ * ^^^^^^^^^^^^^ ^^^^^^^^^^^^^^ ^^^^^^
+ *
+ * Each of these will become a UBO range.
+ */
while (offsets != 0) {
+ /* Find the first 1 in the offsets bitfield. This represents the
+ * start of a range of interesting UBO data. Make it zero-indexed.
+ */
int first_bit = ffsll(offsets) - 1;
+
+ /* Find the first 0 bit in offsets beyond first_bit. To find the
+ * first zero bit, we find the first 1 bit in the complement. In
+ * order to ignore bits before first_bit, we mask off those bits.
+ */
int first_hole = ffsll(~offsets & ~((1ull << first_bit) - 1)) - 1;
+
if (first_hole == -1) {
+ /* If we didn't find a hole, then set it to the end of the
+ * bitfield. There are no more ranges to process.
+ */
first_hole = 64;
offsets = 0;
} else {
+ /* We've processed all bits before first_hole. Mask them off. */
offsets &= ~((1ull << first_hole) - 1);
}
@@ -214,6 +239,7 @@ brw_nir_analyze_ubo_ranges(const struct brw_compiler
*compiler,
entry->range.block = b;
entry->range.start = first_bit;
+ /* first_hole is one beyond the end, so we don't need to add 1 */
entry->range.length = first_hole - first_bit;
entry->benefit = 0;
--
2.13.2
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