diff mbox series

tree-optimization/114203 - wrong CLZ niter computation

Message ID 20240304104515.500153858C54@sourceware.org
State Accepted
Headers
Series tree-optimization/114203 - wrong CLZ niter computation |

Checks

Context Check Description
snail/gcc-patch-check success Github commit url

Commit Message

Richard Biener March 4, 2024, 10:44 a.m. UTC 
  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.

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

	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.
---
 gcc/testsuite/gcc.dg/torture/pr114203.c | 21 +++++++++++++++++++++
 gcc/tree-ssa-loop-niter.cc              |  7 +++----
 2 files changed, 24 insertions(+), 4 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/torture/pr114203.c
diff mbox series

Patch

diff --git a/gcc/testsuite/gcc.dg/torture/pr114203.c b/gcc/testsuite/gcc.dg/torture/pr114203.c
new file mode 100644
index 00000000000..0ef6279942a
--- /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 038e4331661..c6d010f6d89 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;