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tree-optimization/114203 - wrong CLZ niter computation

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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.

	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.
This commit is contained in:
Richard Biener 2024-03-04 10:38:31 +01:00
parent 324d2907c8
commit cde50296a1
2 changed files with 24 additions and 4 deletions
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21
gcc/testsuite/gcc.dg/torture/pr114203.c Normal file
View file

@ -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;
}

7
gcc/tree-ssa-loop-niter.cc
View file

@ -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;