llvmpipe: lp_build_gather_elem_vec BE fix for 3x16 load

Fix loading of a 3x16 vector as a single 48-bit load
on big-endian systems (PPC64, S390).

Roland Scheidegger's commit e827d9175675aaa6cfc0b981e2a80685fb7b3a74
plus Ray Strode's patch reduce pre-Roland Piglit failures from ~4000 to ~2000.  This patch fixes
three of the four regressions observed by Ray:

- draw-vertices
- draw-vertices-half-float
- draw-vertices-half-float_gles2

One regression remains:
- draw-vertices-2101010

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=100613
Cc: "17.2" "17.1" <[email protected]>

Signed-off-by: Ben Crocker <[email protected]>
Reviewed-by: Roland Scheidegger <[email protected]>
(cherry picked from commit 57c8ead0cd08e6aaf88a389f7ce528c4f0face65)

1 files changed, 28 insertions, 2 deletions

diff --git a/src/gallium/auxiliary/gallivm/lp_bld_gather.c b/src/gallium/auxiliary/gallivm/lp_bld_gather.c
index ccd03765c73..7d11dcd3b64 100644
--- a/src/gallium/auxiliary/gallivm/lp_bld_gather.c
+++ b/src/gallium/auxiliary/gallivm/lp_bld_gather.c
@@ -234,13 +234,39 @@ lp_build_gather_elem_vec(struct gallivm_state *gallivm,
           */
          res = LLVMBuildZExt(gallivm->builder, res, dst_elem_type, "");
 
-         if (vector_justify) {
 #ifdef PIPE_ARCH_BIG_ENDIAN
+         if (vector_justify) {
          res = LLVMBuildShl(gallivm->builder, res,
                             LLVMConstInt(dst_elem_type,
                                          dst_type.width - src_width, 0), "");
-#endif
          }
+         if (src_width == 48) {
+            /* Load 3x16 bit vector.
+             * The sequence of loads on big-endian hardware proceeds as follows.
+             * 16-bit fields are denoted by X, Y, Z, and 0.  In memory, the sequence
+             * of three fields appears in the order X, Y, Z.
+             *
+             * Load 32-bit word: 0.0.X.Y
+             * Load 16-bit halfword: 0.0.0.Z
+             * Rotate left: 0.X.Y.0
+             * Bitwise OR: 0.X.Y.Z
+             *
+             * The order in which we need the fields in the result is 0.Z.Y.X,
+             * the same as on little-endian; permute 16-bit fields accordingly
+             * within 64-bit register:
+             */
+            LLVMValueRef shuffles[4] = {
+               lp_build_const_int32(gallivm, 2),
+               lp_build_const_int32(gallivm, 1),
+               lp_build_const_int32(gallivm, 0),
+               lp_build_const_int32(gallivm, 3),
+            };
+            res = LLVMBuildBitCast(gallivm->builder, res,
+                                   lp_build_vec_type(gallivm, lp_type_uint_vec(16, 4*16)), "");
+            res = LLVMBuildShuffleVector(gallivm->builder, res, res, LLVMConstVector(shuffles, 4), "");
+            res = LLVMBuildBitCast(gallivm->builder, res, dst_elem_type, "");
+         }
+#endif
       }
    }
    return res;