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From: "bergner at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug rtl-optimization/35371] New: Missing REG_POINTER attribute causes bad indexed load/store operand ordering Date: Mon, 25 Feb 2008 20:05:00 -0000 [thread overview] Message-ID: <bug-35371-11700@http.gcc.gnu.org/bugzilla/> (raw) We fail to correctly order the operands for the indexed store within the loop below. This seems to be caused by a missing REG_POINTER attribute, so the code added for PR28690 doesn't have a chance of getting the ordering correct. An interesting thing is that if we replace the global array with an "extern int *reg_values;", then we get the ordering correct. bergner@etna:~/gcc/tests> cat a2-loop.c int reg_values[1024]; void clear_table (unsigned int n) { unsigned int i; for (i = 0; i < n; i++) reg_values[i] = 0; } The "bad" code gen looks like (using -O2 -S): clear_table: cmpwi 0,3,0 beqlr- 0 lis 9,reg_values@ha slwi 3,3,2 la 9,reg_values@l(9) li 11,0 li 0,0 .p2align 4,,15 .L3: stwx 0,11,9 addi 11,11,4 cmpw 7,11,3 bne+ 7,.L3 blr It's another question on why this isn't using an update form store and branch on count loop, to halve the size of the loop. The loop size is particularly glaring when you use -O2 -funroll-loops, then we get 8 indexed stores (all with the wrong operand order) and 8 addi's...but I guess that's for another bugzilla. -- Summary: Missing REG_POINTER attribute causes bad indexed load/store operand ordering Product: gcc Version: 4.4.0 Status: UNCONFIRMED Keywords: missed-optimization Severity: normal Priority: P3 Component: rtl-optimization AssignedTo: bergner at gcc dot gnu dot org ReportedBy: bergner at gcc dot gnu dot org GCC build triplet: powerpc64-linux GCC host triplet: powerpc64-linux GCC target triplet: powerpc64-linux http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35371
next reply other threads:[~2008-02-25 20:05 UTC|newest] Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top 2008-02-25 20:05 bergner at gcc dot gnu dot org [this message] 2008-02-25 20:51 ` [Bug rtl-optimization/35371] " bergner at gcc dot gnu dot org 2008-02-26 1:56 ` bergner at gcc dot gnu dot org 2008-02-26 1:57 ` bergner at gcc dot gnu dot org 2008-04-08 15:42 ` bergner at gcc dot gnu dot org
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