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 fn is CFN_CLZ, use CLZ_DEFINED_VALUE_AT.

(cherry picked from commit b82a816000791e7a286c7836b3a473ec0e2a577b)

diff --git a/gcc/fold-const.cc b/gcc/fold-const.cc
index 70302943cea4b40d99e606162700a91cbf0e1240..d81a71c41a1765cee602b69b912a0d414efaadc1 100644 (file)
--- a/gcc/fold-const.cc
+++ b/gcc/fold-const.cc
@@ -84,6 +84,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "vec-perm-indices.h"
 #include "asan.h"
 #include "gimple-range.h"
+#include "internal-fn.h"
 
 /* Nonzero if we are folding constants inside an initializer or a C++
    manifestly-constant-evaluated context; zero otherwise.
@@ -14861,7 +14862,6 @@ 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:
@@ -14870,6 +14870,22 @@ tree_call_nonnegative_warnv_p (tree type, combined_fn fn, tree arg0, tree arg1,
       /* Always true.  */
       return true;
 
+    CASE_CFN_CLZ:
+      if (fn != CFN_CLZ)
+       return true;
+      else if (INTEGRAL_TYPE_P (TREE_TYPE (arg0)))
+       {
+         tree atype = TREE_TYPE (arg0);
+         int val = 0;
+         if (direct_internal_fn_supported_p (IFN_CLZ, atype,
+                                             OPTIMIZE_FOR_BOTH)
+             && CLZ_DEFINED_VALUE_AT_ZERO (SCALAR_INT_TYPE_MODE (atype),
+                                           val) == 2
+             && val >= 0)
+           return true;
+       }
+      break;
+
     CASE_CFN_SQRT:
     CASE_CFN_SQRT_FN:
       /* sqrt(-0.0) is -0.0.  */