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

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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.

(cherry picked from commit b82a816000791e7a286c7836b3a473ec0e2a577b)
This commit is contained in:
Jakub Jelinek 2024-06-04 15:49:41 +02:00
parent f9af4a05e0
commit a88e13bd7e
2 changed files with 34 additions and 1 deletions
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6
gcc/fold-const.cc
View file

@ -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. */

29
gcc/testsuite/gcc.dg/bitint-106.c Normal file
View file

@ -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 ();
}