c/7594: 3.1.1, 3.2 branch ICE on legal code

c/7594: 3.1.1, 3.2 branch ICE on legal code

[Richard Zidlicky]

>Number:         7594
>Category:       c
>Synopsis:       ICE on legal code
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          ice-on-legal-code
>Submitter-Id:   net
>Arrival-Date:   Wed Aug 14 04:36:01 PDT 2002
>Closed-Date:
>Last-Modified:
>Originator:     Richard Zidlicky
>Release:        3.2 20020806 (prerelease) and 3.1.1
>Organization:
>Environment:
native and crosscompiled
configured with: ../gcc-3.2-cvs/configure --enable-languages=c --disable-checking --with-newlib --without-headers --target=m68k-linux : (reconfigured) ../gcc-3.2-cvs/configure --enable-languages=c --disable-checking --with-newlib --without-headers --target=m68k-linux
>Description:

following testcase triggers ICE:

#### compile with -O0 to trigger ICE ####

extern void (**table)(void);

typedef unsigned short uw16;
typedef unsigned short uw16;
typedef unsigned int gshort;

register uw16 *pc asm("%a4");
register gshort code asm("%d6");


void QMExecuteLoop(uw16 *oldPC)
{
            table[code=(*(uw16*)(pc++))]();
}

########################################

Problem is caused by gen_lowpart() returning a REG instead of an
SUBREG expression in certain cases. This is caused by some code
in simplify_subreg around lines 2644 in simplify-rtx.c


>How-To-Repeat:
>Fix:

Workaround for m68k-linux is to disable the code responsible
for this simplification:

--- gcc-3.2-cvs/gcc/simplify-rtx.c.rz   Wed Mar  6 23:43:21 2002
+++ gcc-3.2-cvs/gcc/simplify-rtx.c      Wed Aug 14 13:09:30 2002
@@ -2618,6 +2618,7 @@
      suppress this simplification.  If the hard register is the stack,
      frame, or argument pointer, leave this as a SUBREG.  */
 
+#if 0
   if (REG_P (op)
       && (! REG_FUNCTION_VALUE_P (op)
          || ! rtx_equal_function_value_matters)
@@ -2662,6 +2663,7 @@
          return x;
        }
     }
+#endif
 
   /* If we have a SUBREG of a register that we are replacing and we are
      replacing it with a MEM, make a new MEM and try replacing the


>Release-Note:
>Audit-Trail:
>Unformatted: