On 7/9/24 11:15 PM, Richard Sandiford wrote:
In this PR, due to the -f flags, we ended up with:
bb1: r10=r10
...
bb2: r10=r10
...
bb3: ...=r10
with bb1->bb2 and bb1->bb3.
late-combine successfully combined the bb1->bb2 def-use and set
the insn code to NOOP_MOVE_INSN_CODE. The bb1->bb3 combination
then failed for... reasons. At this point, everything should have
been rewound to its original state.
However, substituting r10=r10 into r10=r10 gives r10=r10, and
validate_change had an early-out for no-op rtl changes. This meant
that validate_change did not register a change for the bb2 insn and
so did not save its old insn code. The NOOP_MOVE_INSN_CODE therefore
persisted even after the attempt had been rewound.
IMO it'd be too cumbersome and error-prone to expect all users of
validate_change to be aware of this possibility. If code is using
validate_change with in_group=1, I think it has a reasonable expectation
that a change will be registered and that the insn code will be saved
(and restored on cancel). This patch therefore limits the shortcut
to the !in_group case.
Bootstrapped & regression-tested on aarch64-linux-gnu & x86_64-linux-gnu.
OK to install?
Richard
gcc/
PR rtl-optimization/115782
* recog.cc (validate_change_1): Suppress early exit for no-op
changes that are part of a group.
gcc/testsuite/
PR rtl-optimization/115782
* gcc.dg/pr115782.c: New test.
OK
jeff
