fold-const: Fix up CLZ handling in tree_call_nonnegative_warnv_p [PR115337]

The function currently incorrectly assumes all the __builtin_clz* and .CLZ
calls have non-negative result.  That is the case of the former which is UB
on zero and has [0, prec-1] return value otherwise, and is the case of the
single argument .CLZ as well (again, UB on zero), but for two argument
.CLZ is the case only if the second argument is also nonnegative (or if we
know the argument can't be zero, but let's do that just in the ranger IMHO).

The following patch does that.

2024-06-04  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/115337
	* fold-const.cc (tree_call_nonnegative_warnv_p) <CASE_CFN_CLZ>:
	If arg1 is non-NULL, RECURSE on it, otherwise return true.

	* gcc.dg/bitint-106.c: New test.

diff --git a/gcc/fold-const.cc b/gcc/fold-const.cc
index 117a816fec62258b7050cdc15d0f793a4e220226..65ce03d572fc391212b64b1d9703bbb88119a2c5 100644 (file)
--- a/gcc/fold-const.cc
+++ b/gcc/fold-const.cc
@@ -15241,7 +15241,6 @@ tree_call_nonnegative_warnv_p (tree type, combined_fn fn, tree arg0, tree arg1,
     CASE_CFN_FFS:
     CASE_CFN_PARITY:
     CASE_CFN_POPCOUNT:
-    CASE_CFN_CLZ:
     CASE_CFN_CLRSB:
     case CFN_BUILT_IN_BSWAP16:
     case CFN_BUILT_IN_BSWAP32:
@@ -15250,6 +15249,11 @@ tree_call_nonnegative_warnv_p (tree type, combined_fn fn, tree arg0, tree arg1,
       /* Always true.  */
       return true;
 
+    CASE_CFN_CLZ:
+      if (arg1)
+       return RECURSE (arg1);
+      return true;
+
     CASE_CFN_SQRT:
     CASE_CFN_SQRT_FN:
       /* sqrt(-0.0) is -0.0.  */

diff --git a/gcc/testsuite/gcc.dg/bitint-106.c b/gcc/testsuite/gcc.dg/bitint-106.c
new file mode 100644 (file)
index 0000000..a36e883
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/bitint-106.c
@@ -0,0 +1,29 @@
+/* PR tree-optimization/115337 */
+/* { dg-do run { target bitint } } */
+/* { dg-options "-O2" } */
+
+#if __BITINT_MAXWIDTH__ >= 129
+#define N 128
+#else
+#define N 63
+#endif
+
+_BitInt (N) g;
+int c;
+
+void
+foo (unsigned _BitInt (N + 1) z, _BitInt (N) *ret)
+{
+  c = __builtin_stdc_first_leading_one (z << N);
+  _BitInt (N) y = *(_BitInt (N) *) __builtin_memset (&g, c, 5);
+  *ret = y;
+}
+
+int
+main ()
+{
+  _BitInt (N) x;
+  foo (0, &x);
+  if (c || g || x)
+    __builtin_abort ();
+}