[Mesa-dev] [PATCH] llvmpipe: improve alignment calculation for fetching/storing pixels

[sroland at vmware.com]

From: Roland Scheidegger <sroland at vmware.com>

This was always doing per-pixel alignment which isn't necessary, except
for the buffer case (due to the per-element offset). The disabled code
for calculating it was incorrect because it assumed that always the full
block would be fetched, which may not be the case, so fix this up.
---
 src/gallium/drivers/llvmpipe/lp_state_fs.c |   33 ++++++++++++++++++----------
 1 file changed, 21 insertions(+), 12 deletions(-)

diff --git a/src/gallium/drivers/llvmpipe/lp_state_fs.c b/src/gallium/drivers/llvmpipe/lp_state_fs.c
index 79f9ef6..28eea3f 100644
--- a/src/gallium/drivers/llvmpipe/lp_state_fs.c
+++ b/src/gallium/drivers/llvmpipe/lp_state_fs.c
@@ -1383,18 +1383,6 @@ generate_unswizzled_blend(struct gallivm_state *gallivm,
       fs_mask[i] = lp_build_zero(gallivm, mask_type);
    }
 
-   /* Compute the alignment of the destination pointer in bytes */
-#if 0
-   dst_alignment = (block_width * out_format_desc->block.bits + 7)/(out_format_desc->block.width * 8);
-#else
-   /* FIXME -- currently we're fetching pixels one by one, instead of row by row */
-   dst_alignment = (1 * out_format_desc->block.bits + 7)/(out_format_desc->block.width * 8);
-#endif
-   /* Force power-of-two alignment by extracting only the least-significant-bit */
-   dst_alignment = 1 << (ffs(dst_alignment) - 1);
-   /* Resource base and stride pointers are aligned to 16 bytes, so that's the maximum alignment we can guarantee */
-   dst_alignment = MIN2(dst_alignment, 16);
-
    /* Do not bother executing code when mask is empty.. */
    if (do_branch) {
       check_mask = LLVMConstNull(lp_build_int_vec_type(gallivm, mask_type));
@@ -1718,6 +1706,27 @@ generate_unswizzled_blend(struct gallivm_state *gallivm,
       dst_type.length = block_width;
    }
 
+   /*
+    * Compute the alignment of the destination pointer in bytes
+    * We fetch 1-4 pixels, if the format has pot alignment then those fetches
+    * are always aligned by MIN2(16, fetch_width) except for buffers (not
+    * 1d tex but can't distinguish here) so need to stick with per-pixel
+    * alignment in this case.
+    */
+   if (is_1d) {
+      dst_alignment = (out_format_desc->block.bits + 7)/(out_format_desc->block.width * 8);
+   }
+   else {
+      dst_alignment = dst_type.length * dst_type.width / 8;
+   }
+   /* Force power-of-two alignment by extracting only the least-significant-bit */
+   dst_alignment = 1 << (ffs(dst_alignment) - 1);
+   /*
+    * Resource base and stride pointers are aligned to 16 bytes, so that's
+    * the maximum alignment we can guarantee
+    */
+   dst_alignment = MIN2(16, dst_alignment);
+
    if (is_1d) {
       load_unswizzled_block(gallivm, color_ptr, stride, block_width, 1,
                             dst, dst_type, dst_count / 4, dst_alignment);
-- 
1.7.9.5