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gallivm: Update comments and prototype of vector-selects. 

No runtime behavior change. As vector selects are still not very well
supported by LLVM.
This commit is contained in:
José Fonseca 2012-02-18 12:02:17 +00:00
parent b5653880f6
commit 8c34a41278
1 changed files with 31 additions and 20 deletions
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51
src/gallium/auxiliary/gallivm/lp_bld_logic.c
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@ -458,6 +458,33 @@ lp_build_select(struct lp_build_context *bld,
mask = LLVMBuildTrunc(builder, mask, LLVMInt1TypeInContext(lc), "");
res = LLVMBuildSelect(builder, mask, a, b, "");
}
else if (0) {
/* Generate a vector select.
*
* XXX: Using vector selects would avoid emitting intrinsics, but they aren't
* properly supported yet.
*
* LLVM 3.0 includes experimental support provided the -promote-elements
* options is passed to LLVM's command line (e.g., via
* llvm::cl::ParseCommandLineOptions), but resulting code quality is much
* worse, probably because some optimization passes don't know how to
* handle vector selects.
*
* See also:
* - http://lists.cs.uiuc.edu/pipermail/llvmdev/2011-October/043659.html
*/
/* Convert the mask to a vector of booleans.
* XXX: There are two ways to do this. Decide what's best.
*/
if (1) {
LLVMTypeRef bool_vec_type = LLVMVectorType(LLVMInt1TypeInContext(lc), type.length);
mask = LLVMBuildTrunc(builder, mask, bool_vec_type, "");
} else {
mask = LLVMBuildICmp(builder, LLVMIntNE, mask, LLVMConstNull(bld->int_vec_type), "");
}
res = LLVMBuildSelect(builder, mask, a, b, "");
}
else if (util_cpu_caps.has_sse4_1 &&
type.width * type.length == 128 &&
!LLVMIsConstant(a) &&
@ -538,13 +565,11 @@ lp_build_select_aos(struct lp_build_context *bld,
return bld->undef;
/*
* There are three major ways of accomplishing this:
* - with a shuffle,
* - with a select,
* - or with a bit mask.
* There are two major ways of accomplishing this:
* - with a shuffle
* - with a select
*
* Select isn't supported for vector types yet.
* The flip between these is empirical and might need to be.
* The flip between these is empirical and might need to be adjusted.
*/
if (n <= 4) {
/*
@ -562,21 +587,7 @@ lp_build_select_aos(struct lp_build_context *bld,
return LLVMBuildShuffleVector(builder, a, b, LLVMConstVector(shuffles, n), "");
}
else {
#if 0
/* XXX: Unfortunately select of vectors do not work */
/* Use a select */
LLVMTypeRef elem_type = LLVMInt1Type();
LLVMValueRef cond_vec[LP_MAX_VECTOR_LENGTH];
for(j = 0; j < n; j += 4)
for(i = 0; i < 4; ++i)
cond_vec[j + i] = LLVMConstInt(elem_type,
mask & (1 << i) ? 1 : 0, 0);
return LLVMBuildSelect(builder, LLVMConstVector(cond_vec, n), a, b, "");
#else
LLVMValueRef mask_vec = lp_build_const_mask_aos(bld->gallivm, type, mask);
return lp_build_select(bld, mask_vec, a, b);
#endif
}
}