fold-const: Punt on MULT_EXPR in extract_muldiv MIN/MAX_EXPR case [PR111151]

fold-const: Punt on MULT_EXPR in extract_muldiv MIN/MAX_EXPR case [PR111151]

As I've tried to explain in the comments, the extract_muldiv_1
MIN/MAX_EXPR optimization is wrong for code == MULT_EXPR.
If the multiplication is done in unsigned type or in signed
type with -fwrapv, it is fairly obvious that max (a, b) * c
in many cases isn't equivalent to max (a * c, b * c) (or min if c is
negative) due to overflows, but even for signed with undefined overflow,
the optimization could turn something without UB in it (where
say a * c invokes UB, but max (or min) picks the other operand where
b * c doesn't).
As for division/modulo, I think it is in most cases safe, except if
the problematic INT_MIN / -1 case could be triggered, but we can
just punt for MAX_EXPR because for MIN_EXPR if one operand is INT_MIN,
we'd pick that operand already.  It is just for completeness, match.pd
already has an optimization which turns x / -1 into -x, so the division
by zero is mostly theoretical.  That is also why in the testcase the
i case isn't actually miscompiled without the patch, while the c and f
cases are.

2024-03-26  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/111151
	* fold-const.cc (extract_muldiv_1) <case MAX_EXPR>: Punt for
	MULT_EXPR altogether, or for MAX_EXPR if c is -1.

	* gcc.c-torture/execute/pr111151.c: New test.