[Bug middle-end/97073] [8/9/10/11 Regression] Miscompilation with -m32 -O1 -march=i686
cvs-commit at gcc dot gnu.org
gcc-bugzilla@gcc.gnu.org
Sun Sep 27 21:26:16 GMT 2020
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97073
--- Comment #11 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-9 branch has been updated by Jakub Jelinek
<jakub@gcc.gnu.org>:
https://gcc.gnu.org/g:aa42c1ac24a0427a27aec19c483780662cd150b8
commit r9-8943-gaa42c1ac24a0427a27aec19c483780662cd150b8
Author: Jakub Jelinek <jakub@redhat.com>
Date: Sun Sep 27 23:18:26 2020 +0200
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.
(cherry picked from commit a4b31d5807f2bc67c8999b3d53369cf2a5c6e1ec)
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