[PATCH] Fix endless match.pd recursion on cst1 + cst2 + cst3 (PR tree-optimization/84334, take 2)

[Jakub Jelinek]

On Tue, Feb 13, 2018 at 07:04:09PM +0100, Richard Biener wrote:
> On February 13, 2018 6:51:29 PM GMT+01:00, Jakub Jelinek <ja...@redhat.com> 
> wrote:
> >On the following testcase, we recurse infinitely, because
> >we have float re-association enabled, but also rounding-math, so
> >we try to optimize (cst1 + cst2) + cst3 as (cst2 + cst3) + cst1
> >but (cst2 + cst3) doesn't simplify and we try again and optimize
> >it as (cst3 + cst1) + cst2 and then (cst1 + cst2) + cst3 and so on
> >forever.  If @0 is not a CONSTANT_CLASS_P, there is not a problem,
> >if it is, the code just checks if we can actually simplify the
> >operation between cst2 and cst3 into a constant.
> 
> Is there a reason to try simplifying at all for constant @0?  I'd rather not 
> try to avoid all the complex code. 

So like this?  Bootstrapped/regtested on x86_64-linux and i686-linux, ok for
trunk?

2018-02-14  Jakub Jelinek  <ja...@redhat.com>

        PR tree-optimization/84334
        * match.pd ((A +- CST1) +- CST2 -> A + CST3): If A is
        also a CONSTANT_CLASS_P, punt.

        * gcc.dg/pr84334.c: New test.

--- gcc/match.pd.jj     2018-02-13 21:22:19.565979401 +0100
+++ gcc/match.pd        2018-02-14 13:55:06.584668049 +0100
@@ -1733,9 +1733,12 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
               CONSTANT_CLASS_P@2)
      /* If one of the types wraps, use that one.  */
      (if (!ANY_INTEGRAL_TYPE_P (type) || TYPE_OVERFLOW_WRAPS (type))
-      (if (outer_op == PLUS_EXPR)
-       (plus (view_convert @0) (inner_op @2 (view_convert @1)))
-       (minus (view_convert @0) (neg_inner_op @2 (view_convert @1))))
+      /* If all 3 captures are CONSTANT_CLASS_P, punt, as we might recurse
+        forever if something doesn't simplify into a constant.  */
+      (if (!CONSTANT_CLASS_P (@0))
+       (if (outer_op == PLUS_EXPR)
+       (plus (view_convert @0) (inner_op @2 (view_convert @1)))
+       (minus (view_convert @0) (neg_inner_op @2 (view_convert @1)))))
       (if (!ANY_INTEGRAL_TYPE_P (TREE_TYPE (@0))
           || TYPE_OVERFLOW_WRAPS (TREE_TYPE (@0)))
        (if (outer_op == PLUS_EXPR)
--- gcc/testsuite/gcc.dg/pr84334.c.jj   2018-02-14 13:53:36.816683512 +0100
+++ gcc/testsuite/gcc.dg/pr84334.c      2018-02-14 13:53:36.815683512 +0100
@@ -0,0 +1,12 @@
+/* PR tree-optimization/84334 */
+/* { dg-do compile } */
+/* { dg-options "-Ofast -frounding-math" } */
+
+float
+foo (void)
+{
+  float a = 9.999999974752427078783512115478515625e-7f;
+  float b = 1.999999994950485415756702423095703125e-6f;
+  float c = 4.999999873689375817775726318359375e-6f;
+  return a + b + c;
+}


        Jakub