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radeonsi: fix behavior of GLSL findLSB(0)

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12.0 and older need the same fix but elsewhere.

Cc: 13.0 <mesa-stable@lists.freedesktop.org>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>
This commit is contained in:
Marek Olšák 2016-10-26 01:08:15 +02:00
parent e24dc43164
commit 4bf45a6079
1 changed files with 13 additions and 4 deletions
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17
src/gallium/drivers/radeonsi/si_shader_tgsi_alu.c
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@ -491,23 +491,32 @@ static void emit_lsb(const struct lp_build_tgsi_action *action,
struct lp_build_emit_data *emit_data)
{
struct gallivm_state *gallivm = bld_base->base.gallivm;
LLVMBuilderRef builder = gallivm->builder;
LLVMValueRef args[2] = {
emit_data->args[0],
/* The value of 1 means that ffs(x=0) = undef, so LLVM won't
* add special code to check for x=0. The reason is that
* the LLVM behavior for x=0 is different from what we
* need here.
*
* The hardware already implements the correct behavior.
* need here. However, LLVM also assumes that ffs(x) is
* in [0, 31], but GLSL expects that ffs(0) = -1, so
* a conditional assignment to handle 0 is still required.
*/
LLVMConstInt(LLVMInt1TypeInContext(gallivm->context), 1, 0)
};
emit_data->output[emit_data->chan] =
LLVMValueRef lsb =
lp_build_intrinsic(gallivm->builder, "llvm.cttz.i32",
emit_data->dst_type, args, ARRAY_SIZE(args),
LLVMReadNoneAttribute);
/* TODO: We need an intrinsic to skip this conditional. */
/* Check for zero: */
emit_data->output[emit_data->chan] =
LLVMBuildSelect(builder,
LLVMBuildICmp(builder, LLVMIntEQ, args[0],
bld_base->uint_bld.zero, ""),
lp_build_const_int32(gallivm, -1), lsb, "");
}
/* Find the last bit set. */