[PATCH] My fold-const.c change with the requested assertion check

[jimbob at google dot com (Robert Kennedy)]

This is my recent fold-const change (from
http://gcc.gnu.org/ml/gcc-patches/2007-01/msg00108.html) to which
Richard Guenther said, "The fold-const change is ok if you add a
testcase," and to which Mark Mitchell asked that I add an assertion
(see http://gcc.gnu.org/ml/gcc-patches/2007-01/msg00326.html).

So here is the change with a testcase and the assertion.

Bootstrapped and tested on i686-pc-linux-gnu.

	-- Robert

		    ------------------------------

2007-01-08  Robert Kennedy <jimbob@google.com>
	* fold-const.c (fold_comparison): Fold comparisons like (x *
	1000 < 0) to (x < 0).
	* fold-compare-2.c: New test case for fold_comparison.
	
==== //depot2/gcctools/google_vendor_src_branch/gcc/trunk/gcc/fold-const.c#19 - /home/jimbob/clients/jimbob-perforce2-test/gcctools/google_vendor_src_branch/gcc/trunk/gcc/fold-const.c ====
# action=edit type=text
--- gcctools/google_vendor_src_branch/gcc/trunk/gcc/fold-const.c	2007-01-05 14:21:22.000000000 -0800
+++ gcctools/google_vendor_src_branch/gcc/trunk/gcc/fold-const.c	2007-01-05 11:22:44.000000000 -0800
@@ -8172,6 +8172,31 @@
 			    variable2);
     }
 
+  /* Transform comparisons of the form X * C1 CMP 0 to X CMP 0 in the
+     signed arithmetic case.  That form is created by the compiler
+     often enough for folding it to be of value.  One example is in
+     computing loop trip counts after Operator Strength Reduction.  */
+  if (!(flag_wrapv || flag_trapv)
+      && !TYPE_UNSIGNED (TREE_TYPE (arg0))
+      && TREE_CODE (arg0) == MULT_EXPR
+      && (TREE_CODE (TREE_OPERAND (arg0, 1)) == INTEGER_CST
+          && !TREE_OVERFLOW (TREE_OPERAND (arg0, 1)))
+      && integer_zerop (arg1))
+    {
+      tree const1 = TREE_OPERAND (arg0, 1);
+      tree const2 = arg1;                       /* zero */
+      tree variable1 = TREE_OPERAND (arg0, 0);
+      enum tree_code cmp_code = code;
+
+      gcc_assert (!integer_zerop (const1));
+
+      /* If const1 is negative we swap the sense of the comparison.  */
+      if (tree_int_cst_sgn (const1) < 0)
+        cmp_code = swap_tree_comparison (cmp_code);
+
+      return fold_build2 (cmp_code, type, variable1, const2);
+    }
+
   tem = maybe_canonicalize_comparison (code, type, arg0, arg1);
   if (tem)
     return tem;
==== //depot2/gcctools/google_vendor_src_branch/gcc/trunk/gcc/testsuite/gcc.dg/fold-compare-2.c#1 - /home/jimbob/clients/jimbob-perforce2-test/gcctools/google_vendor_src_branch/gcc/trunk/gcc/testsuite/gcc.dg/fold-compare-2.c ====
# action=add type=text
--- /dev/null	1969-12-31 16:00:00.000000000 -0800
+++ gcctools/google_vendor_src_branch/gcc/trunk/gcc/testsuite/gcc.dg/fold-compare-2.c	2007-01-04 16:56:33.000000000 -0800
@@ -0,0 +1,18 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-vrp" } */
+
+extern void abort (void);
+
+int a;
+
+int
+main(void)
+{
+  if (a * 1000 < 0)
+    abort ();
+  if (a * -43 > 0)
+    abort ();
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump-times "Removing basic block" 1 "vrp1" } } */