diff options
| -rw-r--r-- | src/gallium/drivers/radeonsi/si_shader_tgsi_alu.c | 17 |
1 files changed, 13 insertions, 4 deletions
diff --git a/src/gallium/drivers/radeonsi/si_shader_tgsi_alu.c b/src/gallium/drivers/radeonsi/si_shader_tgsi_alu.c index 1ee9afb4658..123ff5d86b0 100644 --- a/src/gallium/drivers/radeonsi/si_shader_tgsi_alu.c +++ b/src/gallium/drivers/radeonsi/si_shader_tgsi_alu.c @@ -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. */ |