When ARMConstantIslandPass cannot find any good locations (i.e., "water") to
place constants, it falls back to inserting unconditional branches to make a
place to put them. My recent change exposed a problem in this area. We may
sometimes append to the same block more than one unconditional branch. The
symptoms of this are that the generated assembly has a branch to an undefined
label and running llc with -debug will cause a seg fault.
This happens more easily since my change to prevent CPEs from moving from
lower to higher addresses as the algorithm iterates, but it could have
happened before. The end of the block may be in range for various constant
pool references, but the insertion point for new CPEs is not right at the end
of the block -- it is at the end of the CPEs that have already been placed
at the end of the block. The insertion point could be out of range. When
that happens, the fallback code will always append another unconditional
branch if the end of the block is in range.
The fix is to only append an unconditional branch if the block does not
already end with one. I also removed a check to see if the constant pool load
instruction is at the end of the block, since that is redundant with
checking if the end of the block is in-range.
There is more to be done here, but I think this fixes the immediate problem.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@84172 91177308-0d34-0410-b5e6-96231b3b80d8
Also fixed a couple of coding style things that crept in. And added more
to the temporary hacked up ARMAsmParser::MatchInstruction() method for testing.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@84040 91177308-0d34-0410-b5e6-96231b3b80d8
multiple instructions, the expansion is done during selection so there is
no need to do anything special during legalization.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@84036 91177308-0d34-0410-b5e6-96231b3b80d8
be in a register. The previous use of ARM address mode 2 was completely
arbitrary and inappropriate for Thumb. Radar 7137468.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@84022 91177308-0d34-0410-b5e6-96231b3b80d8
before its reference is only supported on ARM has not been true for a while.
In fact, until recently, that was only supported for Thumb. Besides that,
CPEs are always a multiple of 4 bytes in size, so inserting a CPE should have
no effect on Thumb alignment.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@83916 91177308-0d34-0410-b5e6-96231b3b80d8
MultiSource/Benchmarks/MiBench/automotive-susan test. The failure has
since been masked by an unrelated change (just randomly), so I don't have
a testcase for this now. Radar 7291928.
The situation where this happened is that a constant pool entry (CPE) was
placed at a lower address than the load that referenced it. There were in
fact 2 CPEs placed at adjacent addresses and referenced by 2 loads that were
close together in the code. The distance from the loads to the CPEs was
right at the limit of what they could handle, so that only one of the CPEs
could be placed within range. On every iteration, the first CPE was found
to be out of range, causing a new CPE to be inserted. The second CPE had
been in range but the newly inserted entry pushed it too far away. Thus the
second CPE was also replaced by a new entry, which in turn pushed the first
CPE out of range. Etc.
Judging from some comments in the code, the initial implementation of this
pass did not support CPEs placed _before_ their references. In the case
where the CPE is placed at a higher address, the key to making the algorithm
terminate is that new CPEs are only inserted at the end of a group of adjacent
CPEs. This is implemented by removing a basic block from the "WaterList"
once it has been used, and then adding the newly inserted CPE block to the
list so that the next insertion will come after it. This avoids the ping-pong
effect where CPEs are repeatedly moved to the beginning of a group of
adjacent CPEs. This does not work when going backwards, however, because the
entries at the end of an adjacent group of CPEs are closer than the CPEs
earlier in the group.
To make this pass terminate, we need to maintain a property that changes can
only happen in some sort of monotonic fashion. The fix used here is to require
that the CPE for a particular constant pool load can only move to lower
addresses. This is a very simple change to the code and should not cause
any significant degradation in the results.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@83902 91177308-0d34-0410-b5e6-96231b3b80d8
lists. Changed ARMAsmParser::MatchRegisterName to return -1 instead of 0 on
errors so 0-15 values could be returned as register numbers. Also added the
rest of the arm register names to the currently hacked up version to allow more
testing. Some changes to ARMAsmParser::ParseOperand to give different errors
for things not yet supported and some additions to the hacked
ARMAsmParser::MatchInstruction to allow more testing for now.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@83673 91177308-0d34-0410-b5e6-96231b3b80d8
