optimization/7409: loop optimization

Bernhard Kaindl bk@suse.de
Fri Jul 26 05:58:00 GMT 2002

On 25 Jul 2002 hpenner@de.ibm.com wrote:
> >Description:
> loop_optimize deletes an insn, which should not be deleted.
> This leads to a abort of an application (tcl).

Yes, it leads to an abort in different 8.x tcl versions when
running the included testsuite on s390x with gcc-3.1.1-cvs,
but it looks like it can be worked around by changing the
-O1 in the Makefile ot -O0 or -O2.

Just to bring all the info together, I append some mails
also describing the problem, a testcase and a proposed fix.

---------- Forwarded message ----------
From: Hartmut Penner <HPENNER@de.ibm.com>
To: mark@codesourcery.com, gcc-patches@gcc.gnu.org
Cc: uweigand@de.ibm.com
Date: Thu, 25 Jul 2002 19:53:53 +0200
Subject: PR 7409/Loop optimization bug patch

A proposed patch for problem described in PR7409 is appended here.
The problem was, that the usage of a register as a parameter was not taken
into acount in the function find_single_use_in_loop.

Index: loop.c
RCS file: /cvs/gcc/gcc/gcc/loop.c,v
retrieving revision 1.389.2.7
diff -u -r1.389.2.7 loop.c
--- loop.c      15 Jun 2002 01:12:04 -0000      1.389.2.7
+++ loop.c      25 Jul 2002 17:41:28 -0000
@@ -3448,6 +3448,19 @@
   const char *fmt = GET_RTX_FORMAT (code);
   int i, j;

+  if (x == PATTERN (insn) && GET_CODE (insn) == CALL_INSN)
+    {
+      rtx link;
+      for (link = CALL_INSN_FUNCTION_USAGE (insn); link; link = XEXP (link, 1))
+       {
+         rtx op, reg;
+         if (GET_CODE (op = XEXP (link, 0)) == USE
+             && GET_CODE (reg = XEXP (op, 0)) == REG)
+           regs->array[REGNO (reg)].single_usage = const0_rtx;
+       }
+    }
   if (code == REG)
     regs->array[REGNO (x)].single_usage
       = (regs->array[REGNO (x)].single_usage != 0

Mit freundlichem Gruß / Best regards,

Hartmut Penner
GCC for S/390 Development

---------- Forwarded message ----------

The testcase is from Tcl and is accessibel there under the name tclUtil
which is the file where the problem appears:


cc -S -g -O1 -fPIC tclUtil.i

This is the assembler code generated to call TclFindElement (only one
place in the file):

        lgfr    %r4,%r8
        la      %r1,184(%r15)
        stg     %r1,160(%r15)
        la      %r1,188(%r15)
        stg     %r1,168(%r15)
        lg      %r2,200(%r15)
        lgr     %r3,%r10
        la      %r5,192(%r15)
+       la      %r6,176(%r15)
        brasl   %r14,TclFindElement@PLT

Adding the line marked with + fixes the passing of a pointer onto the
stack and fixes this particulare case.

There are other cases on tcl which -O1 also cause segementation violations,
I hope that the other cases are also fixed with the patch above, it's likely
that the conditions of the other uses of TclFindElement are similar.

Best Regards
Bernhard Kaindl

Research & Development  SuSE Linux S/390 and zSeries

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