From 677122c9df1b55a791a54426269f7a8ce794f947 Mon Sep 17 00:00:00 2001 From: Richard Biener Date: Wed, 5 Feb 2025 13:17:47 +0100 Subject: rtl-optimization/117922 - disable fold-mem-offsets for highly connected CFG The PR shows fold-mem-offsets taking ages and a lot of memory computing DU/UD chains as that requires the RD problem. The issue is not so much the memory required for the pruned sets but the high CFG connectivity (and that the CFG is cyclic) which makes solving the dataflow problem expensive. The following adds the same limit as the one imposed by GCSE and CPROP. PR rtl-optimization/117922 * fold-mem-offsets.cc (pass_fold_mem_offsets::execute): Do nothing for a highly connected CFG. --- gcc/fold-mem-offsets.cc | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) (limited to 'gcc') diff --git a/gcc/fold-mem-offsets.cc b/gcc/fold-mem-offsets.cc index a816006..c1c9447 100644 --- a/gcc/fold-mem-offsets.cc +++ b/gcc/fold-mem-offsets.cc @@ -35,6 +35,7 @@ along with GCC; see the file COPYING3. If not see #include "df.h" #include "tree-pass.h" #include "cfgrtl.h" +#include "diagnostic-core.h" /* This pass tries to optimize memory offset calculations by moving constants from add instructions to the memory instructions (loads / stores). @@ -841,6 +842,23 @@ do_commit_insn (rtx_insn *insn) unsigned int pass_fold_mem_offsets::execute (function *fn) { + /* Computing UD/DU chains for flow graphs which have a high connectivity + will take a long time and is unlikely to be particularly useful. + + In normal circumstances a cfg should have about twice as many + edges as blocks. But we do not want to punish small functions + which have a couple switch statements. Rather than simply + threshold the number of blocks, uses something with a more + graceful degradation. */ + if (n_edges_for_fn (fn) > 20000 + n_basic_blocks_for_fn (fn) * 4) + { + warning (OPT_Wdisabled_optimization, + "fold-mem-offsets: %d basic blocks and %d edges/basic block", + n_basic_blocks_for_fn (cfun), + n_edges_for_fn (cfun) / n_basic_blocks_for_fn (cfun)); + return 0; + } + df_set_flags (DF_EQ_NOTES + DF_RD_PRUNE_DEAD_DEFS + DF_DEFER_INSN_RESCAN); df_chain_add_problem (DF_UD_CHAIN + DF_DU_CHAIN); df_analyze (); -- cgit v1.1