;
>
> +/* Determine whether LOOP contains floating-point computation. */
> +bool
> +loop_has_FP_comp(struct loop *loop)
> +{
> + rtx set, dest;
This probably should be extended to detect other long latency
operations in the future.
> +
> + if (ix86_tune != PROCESSOR_COREI7_64 &&
> + ix86_tune != PROCESSOR_COREI7_32)
> + return nunroll;
Is it better to generalize it and model the LSD and LSD size in the
target model description? -- probably a different patch for that.
> +
> + /* Look for instructions that store a constant into HImode (16-bit)
> + memory. These require a length-changing prefix and on corei7 are
> + prone to LCP stalls. These stalls can be avoided if the loop
> + is streamed from the loop stream detector. */
> + body = get_loop_body (loop);
> + for (i = 0; i < loop->num_nodes && !found; i++)
> + {
> + bb = body[i];
> +
> + FOR_BB_INSNS (bb, insn)
> + {
> + rtx set_expr;
> + set_expr = single_set (insn);
> + if (set_expr != NULL_RTX
> + && GET_MODE (SET_DEST (set_expr)) == HImode
> + && CONST_INT_P (SET_SRC (set_expr))
> + && MEM_P (SET_DEST (set_expr)))
> + {
> + found = true;
> + break;
> + }
> + }
> + }
> + free (body);
Probably generalize this to handle other long latency FE stalls -- for
now it only handles LCP stalls.
> +
> + if (!found)
> + return nunroll;
> +
> + /* Don't reduce unroll factor in loops with floating point
> + computation, which tend to benefit more heavily from
> + larger unroll factors and are less likely to bottleneck
> + at the decoder. */
> + has_FP = loop_has_FP_comp(loop);
> + if (has_FP)
> + return nunroll;
> +
> + if (dump_file)
> + {
> + fprintf (dump_file,
> + ";; Loop contains HImode store of const (possible LCP
> stalls),\n");
> + fprintf (dump_file,
> + " reduce unroll factor to fit into Loop Stream Detector\n");
> + }
> +
> + /* On corei7 the loop stream detector can hold about 28 instructions, so
> + don't allow unrolling to exceed that. */
> + newunroll = 28 / loop->av_ninsns;
Is 28 number of instructions or number of uOps?
thanks,
David
> + if (newunroll < nunroll)
> + return newunroll;
> +
> + return nunroll;
> +}
> +
> /* Initialize the GCC target structure. */
> #undef TARGET_RETURN_IN_MEMORY
> #define TARGET_RETURN_IN_MEMORY ix86_return_in_memory
> @@ -38685,6 +38755,9 @@ ix86_autovectorize_vector_sizes (void)
> #define TARGET_INIT_LIBFUNCS darwin_rename_builtins
> #endif
>
> +#undef TARGET_LOOP_UNROLL_ADJUST
> +#define TARGET_LOOP_UNROLL_ADJUST ix86_loop_unroll_adjust
> +
> struct gcc_target targetm = TARGET_INITIALIZER;
> ^L
> #include "gt-i386.h"
>
> --
> Teresa Johnson | Software Engineer | tejohn...@google.com | 408-460-2413
