gallivm: fix broken 8-wide s3tc decoding

Brian noticed there was an uninitialized var for the 8-wide case and 128
bit blocks, which made it always crash. Likewise, the 64bit block case
had another crash bug due to type mismatch.
Color decode (used for all s3tc formats) also had a bogus shuffle for
this case, leading to decode artifacts.
Fix these all up, which makes the code actually work 8-wide. Note that
it's still not used - I've verified it works, and the generated assembly
does look quite a bit simpler actually (20-30% less instructions for the
s3tc decode part with avx2), however in practice it still seems to be
sligthly slower for some unknown reason (tested with openarena) on my
haswell box, so for now continue to split things into 4-wide vectors
before decoding.

Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Jose Fonseca <jfonseca@vmware.com>

diff --git a/src/gallium/auxiliary/gallivm/lp_bld_format_s3tc.c b/src/gallium/auxiliary/gallivm/lp_bld_format_s3tc.c
index 90b2be981e4ee43fa2278f784b49762fb453833f..9020aabf337f3f98bb18a20615f86fe620c4fc9e 100644 (file)
--- a/src/gallium/auxiliary/gallivm/lp_bld_format_s3tc.c
+++ b/src/gallium/auxiliary/gallivm/lp_bld_format_s3tc.c
@@ -77,24 +77,17 @@ lp_build_uninterleave2_half(struct gallivm_state *gallivm,
                             unsigned lo_hi)
 {
    LLVMValueRef shuffle, elems[LP_MAX_VECTOR_LENGTH];
-   unsigned i, j;
+   unsigned i;
 
    assert(type.length <= LP_MAX_VECTOR_LENGTH);
    assert(lo_hi < 2);
 
    if (type.length * type.width == 256) {
-      assert(type.length >= 4);
-      for (i = 0, j = 0; i < type.length; ++i) {
-         if (i == type.length / 4) {
-            j = type.length;
-         } else if (i == type.length / 2) {
-            j = type.length / 2;
-         } else if (i == 3 * type.length / 4) {
-            j = 3 * type.length / 4;
-         } else {
-            j += 2;
-         }
-         elems[i] = lp_build_const_int32(gallivm, j + lo_hi);
+      assert(type.length == 8);
+      assert(type.width == 32);
+      static const unsigned shufvals[8] = {0, 2, 8, 10, 4, 6, 12, 14};
+      for (i = 0; i < type.length; ++i) {
+         elems[i] = lp_build_const_int32(gallivm, shufvals[i] + lo_hi);
       }
    } else {
       for (i = 0; i < type.length; ++i) {
@@ -277,7 +270,7 @@ lp_build_gather_s3tc(struct gallivm_state *gallivm,
    }
    else {
       LLVMValueRef tmp[4], cc01, cc23;
-      struct lp_type lp_type32, lp_type64, lp_type32dxt;
+      struct lp_type lp_type32, lp_type64;
       memset(&lp_type32, 0, sizeof lp_type32);
       lp_type32.width = 32;
       lp_type32.length = length;
@@ -309,10 +302,13 @@ lp_build_gather_s3tc(struct gallivm_state *gallivm,
                                               lp_build_const_extend_shuffle(gallivm, 2, 4), "");
          }
          if (length == 8) {
+            struct lp_type lp_type32_4 = {0};
+            lp_type32_4.width = 32;
+            lp_type32_4.length = 4;
             for (i = 0; i < 4; ++i) {
                tmp[0] = elems[i];
                tmp[1] = elems[i+4];
-               elems[i] = lp_build_concat(gallivm, tmp, lp_type32, 2);
+               elems[i] = lp_build_concat(gallivm, tmp, lp_type32_4, 2);
             }
          }
          cc01 = lp_build_interleave2_half(gallivm, lp_type32, elems[0], elems[1], 0);
@@ -811,7 +807,7 @@ s3tc_dxt3_to_rgba_aos(struct gallivm_state *gallivm,
    tmp = lp_build_select(&bld, sel_mask, alpha_low, alpha_hi);
    bit_pos = LLVMBuildAnd(builder, bit_pos,
                           lp_build_const_int_vec(gallivm, type, 0xffffffdf), "");
-   /* Warning: slow shift with per element count */
+   /* Warning: slow shift with per element count (without avx2) */
    /*
     * Could do pshufb here as well - just use appropriate 2 bits in bit_pos
     * to select the right byte with pshufb. Then for the remaining one bit
@@ -1640,7 +1636,6 @@ s3tc_decode_block_dxt5(struct gallivm_state *gallivm,
                           lp_build_const_int_vec(gallivm, type16, 8), "");
    alpha = LLVMBuildBitCast(builder, alpha,  i64t, "");
    shuffle1 = lp_build_const_shuffle1(gallivm, 0, 8);
-   /* XXX this shuffle broken with LLVM 2.8 */
    alpha0 = LLVMBuildShuffleVector(builder, alpha0, alpha0, shuffle1, "");
    alpha1 = LLVMBuildShuffleVector(builder, alpha1, alpha1, shuffle1, "");
 
@@ -2176,6 +2171,9 @@ lp_build_fetch_s3tc_rgba_aos(struct gallivm_state *gallivm,
       return rgba;
    }
 
+   /*
+    * Could use n > 8 here with avx2, but doesn't seem faster.
+    */
    if (n > 4) {
       unsigned count;
       LLVMTypeRef i8_vectype = LLVMVectorType(i8t, 4 * n);