This patch removes most of the trivial cases of weak vtables by pinning them to
a single object file. The memory leaks in this version have been fixed. Thanks
Alexey for pointing them out.
Differential Revision: http://llvm-reviews.chandlerc.com/D2068
Reviewed by Andy
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This change is incorrect. If you delete virtual destructor of both a base class
and a subclass, then the following code:
Base *foo = new Child();
delete foo;
will not cause the destructor for members of Child class. As a result, I observe
plently of memory leaks. Notable examples I investigated are:
ObjectBuffer and ObjectBufferStream, AttributeImpl and StringSAttributeImpl.
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We previously used the default expansion to SELECT_CC, which in turn would
expand to "LHI; BRC; LHI". In most cases it's better to use an IPM-based
sequence instead.
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There are no corresponding patterns for small immediates because they would
prevent the use of fused compare-and-branch instructions.
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Similar to low words, we can use the shorter LLIHL and LLIHH if it turns
out that the other half of the GR64 isn't live.
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This just adds the basics necessary for allocating the upper words to
virtual registers (move, load and store). The move support is parameterised
in a way that makes it easy to handle zero extensions, but the associated
zero-extend patterns are added by a later patch.
The easiest way of testing this seemed to be add a new "h" register
constraint for high words. I don't expect the constraint to be useful
in real inline asms, but it should work, so I didn't try to hide it
behind an option.
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Use subreg_hNN and subreg_lNN for the high and low NN bits of a register.
List the low registers first, so that subreg_l32 also means the low 32
bits of a 128-bit register.
Floats are stored in the upper 32 bits of a 64-bit register, so they
should use subreg_h32 rather than subreg_l32.
No behavioral change intended.
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The backend tries to use block operations like MVC, NC, OC and XC for
simple scalar operations. For correctness reasons, it rejects any case
in which the regions might partially overlap. However, for performance
reasons, it should also reject cases where the regions might be equal,
since the instruction might then not use the fast path.
This fixes a performance regression seen in bzip2. We may want to limit
the optimisation even more in future, or even remove it entirely, but I'll
try with this for now.
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Another patch to avoid duplication of encoding information. Things like
NILF, NILL and NILH are used as both 32-bit and 64-bit instructions.
Here the 64-bit versions are defined as aliases of the 32-bit ones.
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Another patch to reduce the duplication of encoding information.
Rather than define separate patterns for truncating 64-bit stores,
use the 32-bit stores with a subreg. No behavioral changed intended.
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For some reason I never got around to adding these at the same time as
the signed versions. No idea why.
I'm not sure whether this SystemZII::BranchC* stuff is useful, or whether
it should just be replaced with an "is normal" flag. I'll leave that
for later though.
There are some boundary conditions that can be tweaked, such as preferring
unsigned comparisons for equality with [128, 256), and "<= 255" over "< 256",
but again I'll leave those for a separate patch.
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Generalize r188163 to cope with return types other than MVT::i32, just
as the existing visitMemCmpCall code did. I've split this out into a
subroutine so that it can be used for other upcoming patches.
I also noticed that I'd used the wrong API to record the out chain.
It's a load that uses DAG.getRoot() rather than getRoot(), so the out
chain should go on PendingLoads. I don't have a testcase for that because
we don't do any interesting scheduling on z yet.
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r188163 used CLC to implement memcmp. Code that compares the result
directly against zero can test the CC value produced by CLC, but code
that needs an integer result must use IPM. The sequence I'd used was:
ipm <reg>
sll <reg>, 2
sra <reg>, 30
but I'd forgotten that this inverts the order, so that CC==1 ("less")
becomes an integer greater than zero, and CC==2 ("greater") becomes
an integer less than zero. This sequence should only be used if the
CLC arguments are reversed to compensate. The problem then is that
the branch condition must also be reversed when testing the CLC
result directly.
Rather than do that, I went for a different sequence that works with
the natural CLC order:
ipm <reg>
srl <reg>, 28
rll <reg>, <reg>, 31
One advantage of this is that it doesn't clobber CC. A disadvantage
is that any sign extension to 64 bits must be done separately,
rather than being folded into the shifts.
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For now this is restricted to fixed-length comparisons with a length
in the range [1, 256], as for memcpy() and MVC.
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This follows the same lines as the integer code. In the end it seemed
easier to have a second 4-bit mask in TSFlags to specify the compare-like
CC values. That eats one more TSFlags bit than adding a CCHasUnordered
would have done, but it feels more concise.
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This patch just uses a peephole test for "add; compare; branch" sequences
within a single block. The IR optimizers already convert loops to
decrement-and-branch-on-nonzero form in some cases, so even this
simplistic test triggers many times during a clang bootstrap and
projects/test-suite run. It looks like there are still cases where we
need to more strongly prefer branches on nonzero though. E.g. I saw a
case where a loop that started out with a check for 0 ended up with a
check for -1. I'll try to look at that sometime.
I ended up adding the Reference class because MachineInstr::readsRegister()
doesn't check for subregisters (by design, as far as I could tell).
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This also fixes a bug in the predication of LR to LOCR: I'd forgotten
that with these in-place instruction builds, the implicit operands need
to be added manually. I think this was latent until now, but is tested
by int-cmp-45.c. It also adds a CC valid mask to STOC, again tested by
int-cmp-45.c.
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System z branches have a mask to select which of the 4 CC values should
cause the branch to be taken. We can invert a branch by inverting the mask.
However, not all instructions can produce all 4 CC values, so inverting
the branch like this can lead to some oddities. For example, integer
comparisons only produce a CC of 0 (equal), 1 (less) or 2 (greater).
If an integer EQ is reversed to NE before instruction selection,
the branch will test for 1 or 2. If instead the branch is reversed
after instruction selection (by inverting the mask), it will test for
1, 2 or 3. Both are correct, but the second isn't really canonical.
This patch therefore keeps track of which CC values are possible
and uses this when inverting a mask.
Although this is mostly cosmestic, it fixes undefined behavior
for the CIJNLH in branch-08.ll. Another fix would have been
to mask out bit 0 when generating the fused compare and branch,
but the point of this patch is that we shouldn't need to do that
in the first place.
The patch also makes it easier to reuse CC results from other instructions.
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r187116 moved compare-and-branch generation from the instruction-selection
pass to the peephole optimizer (via optimizeCompare). It turns out that even
this is a bit too early. Fused compare-and-branch instructions don't
interact well with predication, where a CC result is needed. They also
make it harder to reuse the CC side-effects of earlier instructions
(not yet implemented, but the subject of a later patch).
Another problem was that the AnalyzeBranch family of routines weren't
handling compares and branches, so we weren't able to reverse the fused
form in cases where we would reverse a separate branch. This could have
been fixed by extending AnalyzeBranch, but given the other problems,
I've instead moved the fusing to the long-branch pass, which is also
responsible for the opposite transformation: splitting out-of-range
compares and branches into separate compares and long branches.
I've added a test for the AnalyzeBranch problem. A test for the
predication problem is included in the next patch, which fixes a bug
in the choice of CC mask.
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r186399 aggressively used the RISBG instruction for immediate ANDs,
both because it can handle some values that AND IMMEDIATE can't,
and because it allows the destination register to be different from
the source. I realized later while implementing the distinct-ops
support that it would be better to leave the choice up to
convertToThreeAddress() instead. The AND IMMEDIATE form is shorter
and is less likely to be cracked.
This is a problem for 32-bit ANDs because we assume that all 32-bit
operations will leave the high word untouched, whereas RISBG used in
this way will either clear the high word or copy it from the source
register. The patch uses the z196 instruction RISBLG for this instead.
This means that z10 will be restricted to NILL, NILH and NILF for
32-bit ANDs, but I think that should be OK for now. Although we're
using z10 as the base architecture, the optimization work is going
to be focused more on z196 and zEC12.
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Before the patch we took advantage of the fact that the compare and
branch are glued together in the selection DAG and fused them together
(where possible) while emitting them. This seemed to work well in practice.
However, fusing the compare so early makes it harder to remove redundant
compares in cases where CC already has a suitable value. This patch
therefore uses the peephole analyzeCompare/optimizeCompareInstr pair of
functions instead.
No behavioral change intended, but it paves the way for a later patch.
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If the source of these instructions is spilled we should load the destination.
If the destination is spilled we should store the source.
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The stack coloring pass has code to delete stores and loads that become
trivially dead after coloring. Extend it to cope with single instructions
that copy from one frame index to another.
The testcase happens to show an example of this kicking in at the moment.
It did occur in Real Code too though.
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This fixes foldMemoryOperandImpl() so that it doesn't create duplicated
frame MMOs. I hadn't realized when writing r185434 that it was the caller's
responsibility to add these.
No behavioural change intended.
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...now that the problem that prompted the restriction has been fixed.
The original spill-02.py was a compromise because at the time I couldn't
find an example that actually failed without the two scavenging slots.
The version included here did.
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Add a mapping from register-based <INSN>R instructions to the corresponding
memory-based <INSN>. Use it to cut down on the number of spill loads.
Some instructions extend their operands from smaller fields, so this
required a new TSFlags field to say how big the unextended operand is.
This optimisation doesn't trigger for C(G)R and CL(G)R because in practice
we always combine those instructions with a branch. Adding a test for every
other case probably seems excessive, but it did catch a missed optimisation
for DSGF (fixed in r185435).
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Try to use MVC when spilling the destination of a simple load or the source
of a simple store. As explained in the comment, this doesn't yet handle
the case where the load or store location is also a frame index, since
that could lead to two simultaneous scavenger spills, something the
backend can't handle yet. spill-02.py tests that this restriction kicks in,
but unfortunately I've not yet found a case that would fail without it.
The volatile trick I used for other scavenger tests doesn't work here
because we can't use MVC for volatile accesses anyway.
I'm planning on relaxing the restriction later, hopefully with a test
that does trigger the problem...
Tests @f8 and @f9 also showed that L(G)RL and ST(G)RL were wrongly
classified as SimpleBDX{Load,Store}. It wouldn't be easy to test for
that bug separately, which is why I didn't split out the fix as a
separate patch.
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This patch adds support for the CRJ and CGRJ instructions. Support for
the immediate forms will be a separate patch.
The architecture has a large number of comparison instructions. I think
it's generally better to concentrate on using the "best" comparison
instruction first and foremost, then only use something like CRJ if
CR really was the natual choice of comparison instruction. The patch
therefore opportunistically converts separate CR and BRC instructions
into a single CRJ while emitting instructions in ISelLowering.
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Before this change, the SystemZ backend would use BRCL for all branches
and only consider shortening them to BRC when generating an object file.
E.g. a branch on equal would use the JGE alias of BRCL in assembly output,
but might be shortened to the JE alias of BRC in ELF output. This was
a useful first step, but it had two problems:
(1) The z assembler isn't traditionally supposed to perform branch shortening
or branch relaxation. We followed this rule by not relaxing branches
in assembler input, but that meant that generating assembly code and
then assembling it would not produce the same result as going directly
to object code; the former would give long branches everywhere, whereas
the latter would use short branches where possible.
(2) Other useful branches, like COMPARE AND BRANCH, do not have long forms.
We would need to do something else before supporting them.
(Although COMPARE AND BRANCH does not change the condition codes,
the plan is to model COMPARE AND BRANCH as a CC-clobbering instruction
during codegen, so that we can safely lower it to a separate compare
and long branch where necessary. This is not a valid transformation
for the assembler proper to make.)
This patch therefore moves branch relaxation to a pre-emit pass.
For now, calls are still shortened from BRASL to BRAS by the assembler,
although this too is not really the traditional behaviour.
The first test takes about 1.5s to run, and there are likely to be
more tests in this vein once further branch types are added. The feeling
on IRC was that 1.5s is a bit much for a single test, so I've restricted
it to SystemZ hosts for now.
The patch exposes (and fixes) some typos in the main CodeGen/SystemZ tests.
A later patch will remove the {{g}}s from that directory.
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