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authorRoland Scheidegger <sroland@vmware.com>2013-06-07 21:20:01 +0200
committerRoland Scheidegger <sroland@vmware.com>2013-06-08 17:33:51 +0200
commit213c207b3ac40ae769afe01b8578f566b5e7840d (patch)
treea2c21acecead6f1e470a04f3afe73260fcb56d68 /src
parent0aca2c6b608b80661cb8fd35eb08195ab95743f5 (diff)
gallivm: work around slow code generated for interleaving 128bit vectors
We use 128bit vector interleave for untwiddling in the blend code (with 256bit vectors). llvm generates terrible code for this for some reason, so instead of generating a shuffle for 2 128bit vectors use a extract/insert shuffle instead (it only seems to matter we're not using 128bit wide vectors for the shuffle). This decreases instruction count of the blend code generated for a rgba8 render target without blending from 169 to 113 with llvm 3.1 and from 136 to 114 in llvm 3.2/3.3, and I got a ~8% (llvm 3.1) and ~5% (3.2/3.3) performance improvement in gears. (The generated code is still not terribly good as we could actually avoid the interleaving completely but llvm can't know this.) Reviewed-by: Jose Fonseca <jfonseca@vmware.com>
Diffstat (limited to 'src')
-rw-r--r--src/gallium/auxiliary/gallivm/lp_bld_pack.c22
1 files changed, 22 insertions, 0 deletions
diff --git a/src/gallium/auxiliary/gallivm/lp_bld_pack.c b/src/gallium/auxiliary/gallivm/lp_bld_pack.c
index 14fcd385798..22a4f5a8fdd 100644
--- a/src/gallium/auxiliary/gallivm/lp_bld_pack.c
+++ b/src/gallium/auxiliary/gallivm/lp_bld_pack.c
@@ -271,6 +271,28 @@ lp_build_interleave2(struct gallivm_state *gallivm,
{
LLVMValueRef shuffle;
+ if (type.length == 2 && type.width == 128 && util_cpu_caps.has_avx) {
+ /*
+ * XXX: This is a workaround for llvm code generation deficiency. Strangely
+ * enough, while this needs vinsertf128/vextractf128 instructions (hence
+ * a natural match when using 2x128bit vectors) the "normal" unpack shuffle
+ * generates code ranging from atrocious (llvm 3.1) to terrible (llvm 3.2, 3.3).
+ * So use some different shuffles instead (the exact shuffles don't seem to
+ * matter, as long as not using 128bit wide vectors, works with 8x32 or 4x64).
+ */
+ struct lp_type tmp_type = type;
+ LLVMValueRef srchalf[2], tmpdst;
+ tmp_type.length = 4;
+ tmp_type.width = 64;
+ a = LLVMBuildBitCast(gallivm->builder, a, lp_build_vec_type(gallivm, tmp_type), "");
+ b = LLVMBuildBitCast(gallivm->builder, b, lp_build_vec_type(gallivm, tmp_type), "");
+ srchalf[0] = lp_build_extract_range(gallivm, a, lo_hi * 2, 2);
+ srchalf[1] = lp_build_extract_range(gallivm, b, lo_hi * 2, 2);
+ tmp_type.length = 2;
+ tmpdst = lp_build_concat(gallivm, srchalf, tmp_type, 2);
+ return LLVMBuildBitCast(gallivm->builder, tmpdst, lp_build_vec_type(gallivm, type), "");
+ }
+
shuffle = lp_build_const_unpack_shuffle(gallivm, type.length, lo_hi);
return LLVMBuildShuffleVector(gallivm->builder, a, b, shuffle, "");