[PATCH] Fix bootstrap/59934

[Jeff Law]

As discussed in the PR, when a port does not have partial integer or 
vector integer modes, expmed_mode_index will not be called with those 
modes.  However, our VRP analysis isn't aware of those constraints and 
has to assume the MODE_PARTIAL_INT and MODE_VECTOR_INT cases could be used.

That in turn can cause a false positive array index out of range 
warning, which is causing the s390 and PA ports to fail to bootstrap.

This patch almost restores the s390x bootstrap -- it's currently failing 
building libjava in stage3.

[ ... ]
                 from 
../../../../../../gcc/libjava/classpath/tools/sun/rmi/rmic/Main.java:58,
                 from <built-in>:3:
../../../../../../gcc/libjava/classpath/tools/external/asm/org/objectweb/asm/util/TraceMethodVisitor.java:286:0: 
note: non-delegitimized UNSPEC UNSPEC_PLTOFF (12) found in variable location
gcj: internal compiler error: Segmentation fault (program jc1)
0x80010353 execute
        ../../gcc/gcc/gcc.c:2841
0x8001060d do_spec_1
        ../../gcc/gcc/gcc.c:4641
0x8001394d process_brace_body
        ../../gcc/gcc/gcc.c:5924
0x8001394d handle_braces
        ../../gcc/gcc/gcc.c:5838
[ ... ]

Regardless, this patch from Jakub is clearly a step forward and I 
believe it's highly unlikely to be the root cause of this stage3 error.

I also bootstrapped and regression tested the patch on 
x86-64-unknown-linux-gnu.  Installed on the trunk.

Andreas -- if you could help with debugging the stage3 libjava 
compilation failure, it'd be greatly appreciated.

Thanks,
Jeff
diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 8405b2e..95a324c 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,10 @@
+2014-01-27  Jakub Jelinek  <ja...@redhat.com>
+
+       PR bootstrap/59934
+       * expmed.h (expmed_mode_index): Rework so that analysis and optimziers
+       know when the MODE_PARTIAL_INT and MODE_VECTOR_INT cases can never be
+       reached.
+
 2014-01-27  James Greenhalgh  <james.greenha...@arm.com>
 
        * common/config/arm/arm-common.c
diff --git a/gcc/expmed.h b/gcc/expmed.h
index 9681e41..4d01d1f 100644
--- a/gcc/expmed.h
+++ b/gcc/expmed.h
@@ -221,12 +221,21 @@ expmed_mode_index (enum machine_mode mode)
     case MODE_INT:
       return mode - MIN_MODE_INT;
     case MODE_PARTIAL_INT:
-      return mode - MIN_MODE_PARTIAL_INT + NUM_MODE_INT;
+      /* If there are no partial integer modes, help the compiler
+        to figure out this will never happen.  See PR59934.  */
+      if (MIN_MODE_PARTIAL_INT != VOIDmode)
+       return mode - MIN_MODE_PARTIAL_INT + NUM_MODE_INT;
+      break;
     case MODE_VECTOR_INT:
-      return mode - MIN_MODE_VECTOR_INT + NUM_MODE_IP_INT;
+      /* If there are no vector integer modes, help the compiler
+        to figure out this will never happen.  See PR59934.  */
+      if (MIN_MODE_VECTOR_INT != VOIDmode)
+       return mode - MIN_MODE_VECTOR_INT + NUM_MODE_IP_INT;
+      break;
     default:
-      gcc_unreachable ();
+      break;
     }
+  gcc_unreachable ();
 }
 
 /* Return a pointer to a boolean contained in EOC indicating whether