[PATCH] tree-optimization/117574 - bougs niter lt-to-ne

[Richard Biener]

When trying to change a IV from IV0 < IV1 to IV0' != IV1' we apply
fancy adjustments to the may_be_zero condition we compute rather
than using the obvious IV0->base >= IV1->base expression (to be
able to use > instead of >=?).  This doesn't seem to go well.

Bootstrapped and tested on x86_64-unknown-linux-gnu.

Can anybody think of what the adjustment by mod is about?

Thanks,
Richard.

        PR tree-optimization/117574
        * tree-ssa-loop-niter.cc (number_of_iterations_lt_to_ne):
        Use the obvious may_be_zero condition.

        * gcc.dg/torture/pr117574-1.c: New testcase.
---
 gcc/testsuite/gcc.dg/torture/pr117574-1.c | 20 +++++++++++++++
 gcc/tree-ssa-loop-niter.cc                | 31 +++++------------------
 2 files changed, 27 insertions(+), 24 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/torture/pr117574-1.c

diff --git a/gcc/testsuite/gcc.dg/torture/pr117574-1.c 
b/gcc/testsuite/gcc.dg/torture/pr117574-1.c
new file mode 100644
index 00000000000..2e99cec13b6
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr117574-1.c
@@ -0,0 +1,20 @@
+/* { dg-do run } */
+
+void abort (void);
+int a, c;
+long b;
+short d;
+static long e(long f, long h, long i) {
+  for (long g = f; g <= h; g += i)
+    b += g;
+  return b;
+}
+int main() {
+  c = 1;
+  for (; c >= 0; c--)
+    ;
+  for (; e(d + 40, d + 76, c + 51) < 4;)
+    ;
+  if (a != 0)
+    abort ();
+}
diff --git a/gcc/tree-ssa-loop-niter.cc b/gcc/tree-ssa-loop-niter.cc
index 9518bf969cd..1be4b552206 100644
--- a/gcc/tree-ssa-loop-niter.cc
+++ b/gcc/tree-ssa-loop-niter.cc
@@ -1200,17 +1200,6 @@ number_of_iterations_lt_to_ne (tree type, affine_iv 
*iv0, affine_iv *iv1,
          if (integer_zerop (assumption))
            return false;
        }
-      if (mpz_cmp (mmod, bnds->below) < 0)
-       noloop = boolean_false_node;
-      else if (POINTER_TYPE_P (type))
-       noloop = fold_build2 (GT_EXPR, boolean_type_node,
-                             iv0->base,
-                             fold_build_pointer_plus (iv1->base, tmod));
-      else
-       noloop = fold_build2 (GT_EXPR, boolean_type_node,
-                             iv0->base,
-                             fold_build2 (PLUS_EXPR, type1,
-                                          iv1->base, tmod));
     }
   else
     {
@@ -1226,21 +1215,15 @@ number_of_iterations_lt_to_ne (tree type, affine_iv 
*iv0, affine_iv *iv1,
          if (integer_zerop (assumption))
            return false;
        }
-      if (mpz_cmp (mmod, bnds->below) < 0)
-       noloop = boolean_false_node;
-      else if (POINTER_TYPE_P (type))
-       noloop = fold_build2 (GT_EXPR, boolean_type_node,
-                             fold_build_pointer_plus (iv0->base,
-                                                      fold_build1 (NEGATE_EXPR,
-                                                                   type1, 
tmod)),
-                             iv1->base);
-      else
-       noloop = fold_build2 (GT_EXPR, boolean_type_node,
-                             fold_build2 (MINUS_EXPR, type1,
-                                          iv0->base, tmod),
-                             iv1->base);
     }
 
+  /* IV0 < IV1 does not loop if IV0->base >= IV1->base.  */
+  if (mpz_cmp (mmod, bnds->below) < 0)
+    noloop = boolean_false_node;
+  else
+    noloop = fold_build2 (GE_EXPR, boolean_type_node,
+                         iv0->base, iv1->base);
+
   if (!integer_nonzerop (assumption))
     niter->assumptions = fold_build2 (TRUTH_AND_EXPR, boolean_type_node,
                                      niter->assumptions,
-- 
2.43.0