tree-optimization/114203 - wrong CLZ niter computation

For precision less than int we apply the adjustment to make it defined
at zero after the adjustment to make it compute CLZ rather than CTZ.
That's wrong.

	PR tree-optimization/114203
	* tree-ssa-loop-niter.cc (build_cltz_expr): Apply CTZ->CLZ
	adjustment before making the result defined at zero.

	* gcc.dg/torture/pr114203.c: New testcase.

diff --git a/gcc/testsuite/gcc.dg/torture/pr114203.c b/gcc/testsuite/gcc.dg/torture/pr114203.c
new file mode 100644 (file)
index 0000000..0ef6279
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr114203.c
@@ -0,0 +1,21 @@
+/* { dg-do run } */
+
+int __attribute__((noipa))
+foo (unsigned char b)
+{
+  int c = 0;
+
+  while (b) {
+      b >>= 1;
+      c++;
+  }
+
+  return c;
+}
+
+int main()
+{
+  if (foo(0) != 0)
+    __builtin_abort ();
+  return 0;
+}

diff --git a/gcc/tree-ssa-loop-niter.cc b/gcc/tree-ssa-loop-niter.cc
index 038e4331661f9206033e620ca5b38ce55909421a..c6d010f6d8948c3a0cf7ff890a0f18b675d4dba0 100644 (file)
--- a/gcc/tree-ssa-loop-niter.cc
+++ b/gcc/tree-ssa-loop-niter.cc
@@ -2288,6 +2288,9 @@ build_cltz_expr (tree src, bool leading, bool define_at_zero)
        src = fold_convert (unsigned_type_node, src);
 
       call = build_call_expr (fn, 1, src);
+      if (leading && prec < i_prec)
+       call = fold_build2 (MINUS_EXPR, integer_type_node, call,
+                           build_int_cst (integer_type_node, i_prec - prec));
       if (define_at_zero)
        {
          tree is_zero = fold_build2 (NE_EXPR, boolean_type_node, src,
@@ -2295,10 +2298,6 @@ build_cltz_expr (tree src, bool leading, bool define_at_zero)
          call = fold_build3 (COND_EXPR, integer_type_node, is_zero, call,
                              build_int_cst (integer_type_node, prec));
        }
-
-      if (leading && prec < i_prec)
-       call = fold_build2 (MINUS_EXPR, integer_type_node, call,
-                           build_int_cst (integer_type_node, i_prec - prec));
     }
 
   return call;