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gallivm: optimize 16bit->32bit gather path a bit

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LLVM can't really optimize anything which crosses scalar/vector boundaries,
so help a bit with some particular gather operations when the width is
expanded (only do it for 16->32bit expansion for now), by doing expansion
after fetch. That is probably a better solution anyway even if llvm would
recognize it, makes for cleaner IR...

Reviewed-by: Jose Fonseca <jfonseca@vmware.com>
This commit is contained in:
Roland Scheidegger 2016-12-06 19:59:51 +01:00
parent fd5f420fbb
commit 8ac3c1bf1a
1 changed files with 38 additions and 2 deletions
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40
src/gallium/auxiliary/gallivm/lp_bld_gather.c
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@ -33,6 +33,7 @@
#include "lp_bld_format.h"
#include "lp_bld_gather.h"
#include "lp_bld_swizzle.h"
#include "lp_bld_type.h"
#include "lp_bld_init.h"
#include "lp_bld_intr.h"
@ -270,17 +271,52 @@ lp_build_gather(struct gallivm_state *gallivm,
LLVMTypeRef dst_elem_type = LLVMIntTypeInContext(gallivm->context, dst_width);
LLVMTypeRef dst_vec_type = LLVMVectorType(dst_elem_type, length);
LLVMTypeRef gather_vec_type = dst_vec_type;
unsigned i;
boolean vec_zext = FALSE;
unsigned gather_width = dst_width;
res = LLVMGetUndef(dst_vec_type);
if (src_width == 16 && dst_width == 32) {
LLVMTypeRef g_elem_type = LLVMIntTypeInContext(gallivm->context, dst_width / 2);
gather_vec_type = LLVMVectorType(g_elem_type, length);
/*
* Note that llvm is never able to optimize zext/insert combos
* directly (i.e. zero the simd reg, then place the elements into
* the appropriate place directly). And 16->32bit zext simd loads
* aren't possible (instead loading to scalar reg first).
* (I think this has to do with scalar/vector transition.)
* No idea about other archs...
* We could do this manually, but instead we just use a vector
* zext, which is simple enough (and, in fact, llvm might optimize
* this away).
* (We're not trying that with other bit widths as that might not be
* easier, in particular with 8 bit values at least with only sse2.)
*/
vec_zext = TRUE;
gather_width = 16;
}
res = LLVMGetUndef(gather_vec_type);
for (i = 0; i < length; ++i) {
LLVMValueRef index = lp_build_const_int32(gallivm, i);
LLVMValueRef elem;
elem = lp_build_gather_elem(gallivm, length,
src_width, dst_width, aligned,
src_width, gather_width, aligned,
base_ptr, offsets, i, vector_justify);
res = LLVMBuildInsertElement(gallivm->builder, res, elem, index, "");
}
if (vec_zext) {
res = LLVMBuildZExt(gallivm->builder, res, dst_vec_type, "");
if (vector_justify) {
#if PIPE_ARCH_BIG_ENDIAN
struct lp_type dst_type;
unsigned sv = dst_width - src_width;
dst_type = lp_type_uint_vec(dst_width, dst_width * length);
res = LLVMBuildShl(gallivm->builder, res,
lp_build_const_int_vec(gallivm, dst_type, sv), "");
#endif
}
}
}
return res;