[PATCH] Fix PR60766

[Richard Biener]

This fixes PR60766, a case where IVOPTs generating signed expressions
from originally unsigned ones breaks because that introduces undefined
overflow and VRP manages to exploit that fact.  The solution is to
use unsigned arithmetic when doing simplification using tree-affine.
In general that's always mandated as that facility doesn't care for
association limits that signed expressions have.  Rather than trying
to address this generally the folllowing fixes the single place
that this bug runs into.

Bootstrapped and tested on x86_64-unknown-linux-gnu, applied to trunk
sofar.

Richard.

2014-04-07  Richard Biener  <rguent...@suse.de>

        PR tree-optimization/60766
        * tree-ssa-loop-ivopts.c (cand_value_at): Compute in an
        unsigned type.
        (may_eliminate_iv): Convert cand_value_at result to desired
        type.

        * gcc.dg/torture/pr60766.c: New testcase.

Index: gcc/tree-ssa-loop-ivopts.c
===================================================================
*** gcc/tree-ssa-loop-ivopts.c  (revision 209181)
--- gcc/tree-ssa-loop-ivopts.c  (working copy)
*************** cand_value_at (struct loop *loop, struct
*** 4236,4243 ****
    tree steptype = type;
    if (POINTER_TYPE_P (type))
      steptype = sizetype;
  
!   tree_to_aff_combination (iv->step, steptype, &step);
    tree_to_aff_combination (niter, TREE_TYPE (niter), &nit);
    aff_combination_convert (&nit, steptype);
    aff_combination_mult (&nit, &step, &delta);
--- 4236,4245 ----
    tree steptype = type;
    if (POINTER_TYPE_P (type))
      steptype = sizetype;
+   steptype = unsigned_type_for (type);
  
!   tree_to_aff_combination (iv->step, TREE_TYPE (iv->step), &step);
!   aff_combination_convert (&step, steptype);
    tree_to_aff_combination (niter, TREE_TYPE (niter), &nit);
    aff_combination_convert (&nit, steptype);
    aff_combination_mult (&nit, &step, &delta);
*************** cand_value_at (struct loop *loop, struct
*** 4245,4250 ****
--- 4247,4254 ----
      aff_combination_add (&delta, &step);
  
    tree_to_aff_combination (iv->base, type, val);
+   if (!POINTER_TYPE_P (type))
+     aff_combination_convert (val, steptype);
    aff_combination_add (val, &delta);
  }
  
*************** may_eliminate_iv (struct ivopts_data *da
*** 4623,4629 ****
  
    cand_value_at (loop, cand, use->stmt, desc->niter, &bnd);
  
!   *bound = aff_combination_to_tree (&bnd);
    *comp = iv_elimination_compare (data, use);
  
    /* It is unlikely that computing the number of iterations using division
--- 4627,4634 ----
  
    cand_value_at (loop, cand, use->stmt, desc->niter, &bnd);
  
!   *bound = fold_convert (TREE_TYPE (cand->iv->base),
!                        aff_combination_to_tree (&bnd));
    *comp = iv_elimination_compare (data, use);
  
    /* It is unlikely that computing the number of iterations using division
Index: gcc/testsuite/gcc.dg/torture/pr60766.c
===================================================================
*** gcc/testsuite/gcc.dg/torture/pr60766.c      (revision 0)
--- gcc/testsuite/gcc.dg/torture/pr60766.c      (working copy)
***************
*** 0 ****
--- 1,15 ----
+ /* { dg-do run } */
+ 
+ int m = 9;
+ 
+ int main()
+ {
+   int n, x;
+ 
+   n = m;
+   for (x = 0; x <= n; x++)
+     if (n == x + (x + 1) + (x + 2))
+       return 0;
+ 
+   __builtin_abort();
+ }