From: Richard Biener <rguenther@suse.de>
Date: Mon, 4 Mar 2024 09:38:31 +0000 (+0100)
Subject: tree-optimization/114203 - wrong CLZ niter computation
X-Git-Tag: basepoints/gcc-15~846
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=cde50296a19b109909089b91d532d2c8455f5f10;p=thirdparty%2Fgcc.git

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
index 000000000000..0ef6279942a8
--- /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 038e4331661f..c6d010f6d894 100644
--- 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;