From 095eb138f736d94dabf9a07a6671bd351be0e66a Mon Sep 17 00:00:00 2001 From: Roger Sayle Date: Fri, 28 Jul 2023 09:39:46 +0100 Subject: [PATCH] PR rtl-optimization/110587: Reduce useless moves in compile-time hog. This patch is one of a series of fixes for PR rtl-optimization/110587, a compile-time regression with -O0, that attempts to address the underlying cause. As noted previously, the pathological test case pr28071.c contains a large number of useless register-to-register moves that can produce quadratic behaviour (in LRA). These moves are generated during RTL expansion in emit_group_load_1, where the middle-end attempts to simplify the source before calling extract_bit_field. This is reasonable if the source is a complex expression (from before the tree-ssa optimizers), or a SUBREG, or a hard register, but it's not particularly useful to copy a pseudo register into a new pseudo register. This patch eliminates that redundancy. The -fdump-tree-expand for pr28071.c compiled with -O0 currently contains 777K lines, with this patch it contains 717K lines, i.e. saving about 60K lines (admittedly of debugging text output, but it makes the point). 2023-07-28 Roger Sayle Richard Biener gcc/ChangeLog PR middle-end/28071 PR rtl-optimization/110587 * expr.cc (emit_group_load_1): Simplify logic for calling force_reg on ORIG_SRC, to avoid making a copy if the source is already in a pseudo register. --- gcc/expr.cc | 13 ++++--------- 1 file changed, 4 insertions(+), 9 deletions(-) diff --git a/gcc/expr.cc b/gcc/expr.cc index fff09dc99510..174f8acb269a 100644 --- a/gcc/expr.cc +++ b/gcc/expr.cc @@ -2622,16 +2622,11 @@ emit_group_load_1 (rtx *tmps, rtx dst, rtx orig_src, tree type, be loaded directly into the destination. */ src = orig_src; if (!MEM_P (orig_src) - && (!CONSTANT_P (orig_src) - || (GET_MODE (orig_src) != mode - && GET_MODE (orig_src) != VOIDmode))) + && (!REG_P (orig_src) || HARD_REGISTER_P (orig_src)) + && !CONSTANT_P (orig_src)) { - if (GET_MODE (orig_src) == VOIDmode) - src = gen_reg_rtx (mode); - else - src = gen_reg_rtx (GET_MODE (orig_src)); - - emit_move_insn (src, orig_src); + gcc_assert (GET_MODE (orig_src) != VOIDmode); + src = force_reg (GET_MODE (orig_src), orig_src); } /* Optimize the access just a bit. */ -- 2.39.5