optabs: Don't reuse target for multi-word expansions if it overlaps operand(s) [PR97073]

The following testcase is miscompiled on i686-linux, because
we try to expand a double-word bitwise logic operation with op0
being a (mem:DI u) and target (mem:DI u+4), i.e. partial overlap, and
thus end up with:
	movl	4(%esp), %eax
	andl	u, %eax
	movl	%eax, u+4
! movl u+4, %eax optimized out
	andl	8(%esp), %eax
	movl	%eax, u+8
rather than with the desired:
	movl	4(%esp), %edx
	movl	8(%esp), %eax
	andl	u, %edx
	andl	u+4, %eax
	movl	%eax, u+8
	movl	%edx, u+4
because the store of the first word to target overwrites the second word of
the operand.
expand_binop for this (and several similar places) already check for target
== op0 or target == op1, this patch just adds reg_overlap_mentioned_p calls
next to it.
Pedantically, at least for some of these it might be sufficient to force
a different target if there is overlap but target is not rtx_equal_p to
the operand (e.g. in this bitwise logical case, but e.g. not in the shift
cases where there is reordering), though that would go against the
preexisting target == op? checks and the rationale that REG_EQUAL notes in
that case isn't correct.

2020-09-27  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/97073
	* optabs.c (expand_binop, expand_absneg_bit, expand_unop,
	expand_copysign_bit): Check reg_overlap_mentioned_p between target
	and operand(s) and if it returns true, force a pseudo as target.

	* gcc.c-torture/execute/pr97073.c: New test.

0 files changed, 0 insertions, 0 deletions