[gcc r15-1011] fold-const: Fix up CLZ handling in tree_call_nonnegative_warnv_p [PR115337]

[Jakub Jelinek]

https://gcc.gnu.org/g:b82a816000791e7a286c7836b3a473ec0e2a577b

commit r15-1011-gb82a816000791e7a286c7836b3a473ec0e2a577b
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Tue Jun 4 15:49:41 2024 +0200

    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:
---
 gcc/fold-const.cc                 |  6 +++++-
 gcc/testsuite/gcc.dg/bitint-106.c | 29 +++++++++++++++++++++++++++++
 2 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/gcc/fold-const.cc b/gcc/fold-const.cc
index 117a816fec6..65ce03d572f 100644
--- 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
index 00000000000..a36e8836690
--- /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 ();
+}