This is a re-apply of D123599, which was reverted in 4fe2ab5279, now
with a more appropriate assertion. Original commit message follow:
InstrRefBasedLDV can track and describe variable values that are spilt to
the stack -- however it does not current describe the size of the value on
the stack. This can cause uninitialized bytes to be read from the stack if
a small register is spilt for a larger variable, or theoretically on
big-endian machines if a large value on the stack is used for a small
variable.
Fix this by using DW_OP_deref_size to specify the amount of data to load
from the stack, if there's any possibility for ambiguity. There are a few
scenarios where this can be omitted (such as when using DW_OP_piece and a
non-DW_OP_stack_value location), see deref-spills-with-size.mir for an
explicit table of inputs flavours and output expressions.
Differential Revision: https://reviews.llvm.org/D123599
This reverts commit a15b66e76d.
This causes linker to crash at assertion: `Assertion failed: !Expr->isComplex(), file C:\b\s\w\ir\cache\builder\src\third_party\llvm\llvm\lib\CodeGen\LiveDebugValues\InstrRefBasedImpl.cpp, line 907`.
InstrRefBasedLDV can track and describe variable values that are spilt to
the stack -- however it does not current describe the size of the value on
the stack. This can cause uninitialized bytes to be read from the stack if
a small register is spilt for a larger variable, or theoretically on
big-endian machines if a large value on the stack is used for a small
variable.
Fix this by using DW_OP_deref_size to specify the amount of data to load
from the stack, if there's any possibility for ambiguity. There are a few
scenarios where this can be omitted (such as when using DW_OP_piece and a
non-DW_OP_stack_value location), see deref-spills-with-size.mir for an
explicit table of inputs flavours and output expressions.
Differential Revision: https://reviews.llvm.org/D123599
This was reverted twice, in 987cd7c3ed and 13815e8cbf. The latter
stemed from not accounting for rare register classes in a pre-allocated
array, and the former from an array not being completely initialized,
leading to asan complaining.
This was applied in fda4305e53, reverted in 13815e8cbf, the problem
was that fp80 X86 registers that were spilt to the stack aren't expected by
LiveDebugValues. It pre-allocates a position number for all register sizes
that can be spilt, and 80 bits isn't exactly common.
The solution is to scan the register classes to find any unrecognised
register sizes, adn pre-allocate those position numbers, avoiding a later
assertion.
DBG_PHI instructions can refer to stack slots, to indicate that multiple
values merge together on control flow joins in that slot. This is fine --
however the slot might be merged at a later date with a slot of a different
size. In doing so, we lose information about the size the eliminated PHI.
Later analysis passes have to guess.
Improve this by attaching an optional "bit size" operand to DBG_PHI, which
only gets added for stack slots, to let us know how large a size the value
on the stack is.
Differential Revision: https://reviews.llvm.org/D124184
This patch adjusts what location is picked for a known variable value --
preferring to leave locations on the stack, even when a value is re-loaded
into a register. The benefit is reduced location list entropy, on a
clang-3.4 build I found that .debug_loclists reduces in size by 6%, from
29Mb down to 27Mb.
Testing: a few tests need the stack slot to be written to explicitly, to
force LiveDebugValues into restoring the variable location to a register.
I've added an explicit test for the desired behaviour in
livedebugvalues_recover_clobbers.mir .
Differential Revision: https://reviews.llvm.org/D120732
This new-ish LEA-fixup code path creates two substitutions for an
instruction number -- this is incorrect because each Value should be
replaced by a single replacement Value. Fix by deleting the duplicate
substitution. Add some test coverage for this path with debug-info
attached.
Differential Revision: https://reviews.llvm.org/D119232
It's inevitable that optimisation passes will fail to update debug-info:
when that happens, it's best if the compiler doesn't crash as a result.
Therefore, downgrade a few assertions / failure modes that would crash
when illegal debug-info was seen, to instead drop variable locations. In
practice this means that an instruction reference to a nonexistant or
illegal operand should be tolerated.
Differential Revision: https://reviews.llvm.org/D118998
This is a follow-up to D117877: variable assignments of DBG_VALUE $noreg,
or DBG_INSTR_REFs where no value can be found, are represented by a
DbgValue object with Kind "Undef", explicitly meaning "there is no value".
In D117877 I added a special-case to some assignment accounting faster,
without considering this scenario. It causes variables to be given the
value ValueIDNum::EmptyValue, which then ends up being a DenseMap key. The
DenseMap asserts, because EmptyValue is the tombstone key.
Fix this by handling the assign-undef scenario in the special case, to
match what happens in the general case: the variable has no value if it's
only ever assigned $noreg / undef.
Differential Revision: https://reviews.llvm.org/D118715
Was reverted in 1c1b670a73 as it broke all non-x86 bots. Original commit
message:
[DebugInfo][InstrRef] Add a max-stack-slots-to-track cut-out
In certain circumstances with things like autogenerated code and asan, you
can end up with thousands of Values live at the same time, causing a large
working set and a lot of information spilled to the stack. Unfortunately
InstrRefBasedLDV doesn't cope well with this and consumes a lot of memory
when there are many many stack slots. See the reproducer in D116821.
It seems very unlikely that a developer would be able to reason about
hundreds of live named local variables at the same time, so a huge working
set and many stack slots is an indicator that we're likely analysing
autogenerated or instrumented code. In those cases: gracefully degrade by
setting an upper bound on the amount of stack slots to track. This limits
peak memory consumption, at the cost of dropping some variable locations,
but in a rare scenario where it's unlikely someone is actually going to
use them.
In terms of the patch, this adds a cl::opt for max number of stack slots to
track, and has the stack-slot-numbering code optionally return None. That
then filters through a number of code paths, which can then chose to not
track a spill / restore if it touches an untracked spill slot. The added
test checks that we drop variable locations that are on the stack, if we
set the limit to zero.
Differential Revision: https://reviews.llvm.org/D118601
In certain circumstances with things like autogenerated code and asan, you
can end up with thousands of Values live at the same time, causing a large
working set and a lot of information spilled to the stack. Unfortunately
InstrRefBasedLDV doesn't cope well with this and consumes a lot of memory
when there are many many stack slots. See the reproducer in D116821.
It seems very unlikely that a developer would be able to reason about
hundreds of live named local variables at the same time, so a huge working
set and many stack slots is an indicator that we're likely analysing
autogenerated or instrumented code. In those cases: gracefully degrade by
setting an upper bound on the amount of stack slots to track. This limits
peak memory consumption, at the cost of dropping some variable locations,
but in a rare scenario where it's unlikely someone is actually going to
use them.
In terms of the patch, this adds a cl::opt for max number of stack slots to
track, and has the stack-slot-numbering code optionally return None. That
then filters through a number of code paths, which can then chose to not
track a spill / restore if it touches an untracked spill slot. The added
test checks that we drop variable locations that are on the stack, if we
set the limit to zero.
Differential Revision: https://reviews.llvm.org/D118601
If we only assign a variable value a single time, we can take a short-cut
when computing its location: the variable value is only valid up to the
dominance frontier of where the assignemnt happens. Past that point, there
are other predecessors from where the variable has no value, meaning the
variable has no location past that point.
This patch recognises this scenario, and avoids expensive SSA computation,
to improve compile-time performance.
Differential Revision: https://reviews.llvm.org/D117877
Shiny new DBG_PHI instruction usually have physical registers as operands
-- however, the machine verifier checks to see whether they're live, and
occasionally this fails. There's a filter for DBG_VALUE instructions to not
get verified in this way: expand it to exempt all debug instructions from
liveness checking, which means DBG_PHIs get treated like DBG_VALUEs.
This also future proofs against us adding new debug instructions.
Differential Revision: https://reviews.llvm.org/D117891
InstrRefBasedLDV used to crash on the added test -- the exit block is not
in scope for the variable being propagated, but is still considered because
it contains an assignment. The failure-mode was vlocJoin ignoring
assign-only blocks and not updating DIExpressions, but pickVPHILoc would
still find a variable location for it. That led to DBG_VALUEs created with
the wrong fragment information.
Fix this by removing a filter inherited from VarLocBasedLDV: vlocJoin will
now consider assign-only blocks and will update their expressions.
Differential Revision: https://reviews.llvm.org/D114727
InstrRefBasedLDV observes when variable locations are clobbered, scans what
values are available in the machine, and re-issues a DBG_VALUE for the
variable if it can find another location. Unfortunately, I hadn't joined up
the Indirectness flag, so if it did this to an Indirect Value, the
indirectness would be dropped.
Fix this, and add a test that if we clobber a variable value (on the stack
in this case), then the recovered variable location keeps the Indirect
flag.
Differential Revision: https://reviews.llvm.org/D114378
Almost all of the time, call instructions don't actually lead to SP being
different after they return. An exception is win32's _chkstk, which which
implements stack probes. We need to recognise that as modifying SP, so
that copies of the value are tracked as distinct vla pointers.
This patch adds a target frame-lowering hook to see whether stack probe
functions will modify the stack pointer, store that in an internal flag,
and if it's true then scan CALL instructions to see whether they're a
stack probe. If they are, recognise them as defining a new stack-pointer
value.
The added test exercises this behaviour: two calls to _chkstk should be
considered as producing two different values.
Differential Revision: https://reviews.llvm.org/D114443
Be more consistent in the naming convention for the various RET instructions to specify in terms of bitwidth.
Helps prevent future scheduler model mismatches like those that were only addressed in D44687.
Differential Revision: https://reviews.llvm.org/D113302
During register allocation, some instructions can have stack spills fused
into them. It means that when vregs are allocated on the stack we can
convert:
SETCCr %0
DBG_VALUE %0
to
SETCCm %stack.0
DBG_VALUE %stack.0
Unfortunately instruction referencing finds this harder: a store to the
stack doesn't have a specific operand number, therefore we don't substitute
the old operand for a new operand, and the location is dropped. This patch
implements a solution: just recognise the memory operand attached to an
instruction with a Special Number (TM), and record a substitution between
the old value and the new one.
This patch adds substitution code to InlineSpiller to record such fused
spills, and tracking in InstrRefBasedLDV to recognise such values, and
produce the value numbers for them. Everything to do with the movement of
stack-defined values is already handled in InstrRefBasedLDV.
Differential Revision: https://reviews.llvm.org/D111317
Sometimes we generate code that writes to a subregister, then spills /
restores a super-register to the stack, for example:
$eax = MOV32ri 0
MOV64mr $rsp, 1, $noreg, 16, $noreg, $rax
$rcx = MOV64rm $rsp, 1, $noreg, 8, $noreg
This patch takes a different approach: it adds another index to
MLocTracker that identifies a size/offset within a stack slot. A location
on the stack is then a pari of {FrameIndex, SlotNum}. Spilling and
restoring now involves pairing up the src/dest register numbers, and the
dest/src stack position to be transferred to/from. Location coverage
improves as a result, compile-time performance decreases, alas.
One limitation is that if a PHI occurs inside a stack slot:
DBG_PHI %stack.0, 1
We don't know how large the resulting value is, and so might have
difficulty picking which value to use. DBG_PHI might need to be augmented
in the future with such a size.
Unit tests added ensure that spills and restores correctly transfer to
positions in the Location => Value map, and that different register classes
written to the stack will correctly clobber all other positions in the
stack slot.
Differential Revision: https://reviews.llvm.org/D112133
This patch is very similar to D110173 / a3936a6c19, but for variable
values rather than machine values. This is for the second instr-ref
problem, calculating the correct variable value on entry to each block.
The previous lattice based implementation was broken; we now use LLVMs
existing PHI placement utilities to work out where values need to merge,
then eliminate un-necessary ones through value propagation.
Most of the deletions here happen in vlocJoin: it was trying to pick a
location for PHIs to happen in, badly, leading to an infinite loop in the
MIR test added, where it would repeatedly switch between register
locations. The new approach is simpler: either PHIs can be eliminated, or
they can't, and the location of the value is a different problem.
Various bits and pieces move to the header so that they can be tested in
the unit tests. The DbgValue class grows a "VPHI" kind to represent
variable value PHIS that haven't been eliminated yet.
Differential Revision: https://reviews.llvm.org/D110630
An important part of the instruction referencing solution is that we
identify all the registers that values move between before we then compute
an SSA-like function from the machine code, and from the variable
intrinsics. DBG_PHIs weren't causing all the subregisters of their operands
to be tracked; this patch forces that to happen.
The practical implications were that not enough space is allocated for
storing values when analysing the function -- asan will crash on the
attached test case with an unpatched compiler. Non-asan llc's will produce
a DBG_VALUE $noreg, where it should be $dil.
Differential Revision: https://reviews.llvm.org/D109064
Stack slot colouring adds "weight" to slots if a non-dbg-value instruction
refers to it. This, unfortunately, means that DBG_PHI instructions can have
an effect on codegen. The fix is very simple, replace isDebugValue with
isDebugInstr.
The regression test contains a scenario that reproduces this problem; I've
represented both normal-debug mode and instr-ref debug mode instructions
in comment lines prefixed with AAAAAA and BBBBBB, and un-comment them with
sed to test that the two different modes produce the same behaviour.
Differential Revision: https://reviews.llvm.org/D108627
Over in D105657, we started dropping instruction numbers (that become
variable locations) from call instructions, as we can't correctly represent
the x87 FP stack. Unfortunately, it turns out that the "special FP
instructions" that this pass transforms includes "every call instruction"
[0]. Thus, we've ended up dropping all return values from all calls. Ouch.
This patch adds a filter: only drop instruction numbers from calls if they
return something on the FP stack. Seeing how LLVM only allows a single
return value, this should drop instruction numbers on anything that returns
a float, and nothing else.
Rather than writing a new test, I've modified the original one to have a
positive and negative case: drop instruction number on a call with an
FP-stack modification, keep it on a plain call.
Differential Revision: https://reviews.llvm.org/D108580
This patch makes InstrRefBasedLDV "safe" to work with DBG_VALUE_LISTs. It
doesn't actually interpret them, but it recognises that they specify
variable locations and avoids propagating false locations, which is better
than the current state. Observe the attached tes
* We avoid propagating DBG_VALUE_LISTs into successor blocks, as they're
not "currently" supported,
* We don't propagate other variable locations across DBG_VALUE_LISTs,
because we know that the variable location is terminated by the
DBG_VALUE_LIST.
Differential Revision: https://reviews.llvm.org/D108143
This patch removes an assertion, and adds a regression test showing why the
assertion is broken.
For context, LocIdx is a key/index number for machine locations, so that we
can describe locations as a single integer and ignore whether they're on
the stack, in registers or otherwise. Back when InstrRefBasedLDV was added,
I happened to bake in a "special" zero number for various reasons, which
Vedant identified as undesirable in this review comment:
https://reviews.llvm.org/D83047#inline-765495 . I subsequently removed that
special zero number, but it looks like I didn't delete this assertion at
the time, which assumes that a zero LocIdx is invalid.
The attached test shows that this assertion is reachable on valid code --
on x86 $rsp always gets the LocIdx number zero, and if you transfer a
variable value into it, InstrRefBasedLDV crashes on that assertion. The
code might be a bit wild to be storing variables to $rsp like that, however
we shouldn't crash on it.
Differential Revision: https://reviews.llvm.org/D108134
This patch fixes a clearly-broken function that I absent-mindedly bodged
many months ago.
Over in D85749 I landed the substituteDebugValuesForInst, that creates
substitution records for all the def operands from one debug-labelled
instruction to the new one. Unfortunately it would crash if the two
instructions had different numbers of operands; I tried to fix this in
537f0fbe82 by adding a "max operand" parameter to the method, but then
didn't actually change the loop bound to take account of this. It passed
all the tests because.... well there wasn't any real test coverage of this
method.
This patch fixes up the loop to be bounded by the MaxOperand bound; and
adds test coverage for the x86-fixup-LEAs calls to this method, so that
it's actually tested.
Differential Revision: https://reviews.llvm.org/D105820
Avoid a crash when using instruction referencing if x87 floating point
instructions are used. These instructions are significantly mutated when
they're rewritten from referring to registers, to referring to
floating-point-stack positions. As a result, their operands are re-ordered,
and (InstrRef) LiveDebugValues asserts when it sees a DBG_INSTR_REF
referring to a non-reg non-def register operand.
To fix this, drop the instruction numbers, and thus variable locations.
This patch adds a helper utility do do that.
Dropping the variable locations is sub-optimal, but applying DBG_VALUEs to
the $fp0 and similar registers is dropped on emission too. It seems we've
never done well at describing variables that live in x87 registers, at all.
Differential Revision: https://reviews.llvm.org/D105657
LLVM provides target hooks to recognise stack spill and restore
instructions, such as isLoadFromStackSlot, and it also provides post frame
elimination versions such as isLoadFromStackSlotPostFE. These are supposed
to return the store-source and load-destination registers; unfortunately on
X86, the PostFE recognisers just return "1", apparently to signify "yes
it's a spill/load". This patch alters the hooks to correctly return the
store-source and load-destination registers:
This is really useful for debug-info as we it helps follow variable values
as they move on/off the stack. There should be no codegen changes: the only
other users of these PostFE target hooks are MachineInstr::getRestoreSize
and MachineInstr::getSpillSize, which don't attempt to interpret the
returned register location.
While we're here, delete the (InstrRef) LiveDebugValues heuristic that
tries to find the spill source register by looking for a killed reg -- we
should be able to rely on the target hooks for that. This involves
temporarily turning off a n InstrRef LivedDebugValues test on aarch64
(patch to re-enable it is in D104521).
Differential Revision: https://reviews.llvm.org/D105428
This is a cleanup patch -- we're now able to support all flavours of
variable location in instruction referencing mode. This patch updates
various tests for debug instructions to be broader: numerous code paths
try to ignore debug isntructions, and they now have to ignore the
additional DBG_PHI and DBG_INSTR_REFs that we can generate.
A small amount of rework happens for LiveDebugVariables: as we don't need
to track live intervals through regalloc any more, we can get away with
unlinking debug instructions before regalloc, then re-inserting them after.
Note that this isn't (yet) true of DBG_VALUE_LISTs, they still have to go
through live interval tracking.
In SelectionDAG, add a helper lambda that emits half-formed DBG_INSTR_REFs
for arguments in instr-ref mode, DBG_VALUE otherwise. This is one of the
final locations where DBG_VALUEs are emitted for vreg arguments.
X86InstrInfo now un-sets the debug instr number on SUB instructions that
get mutated into CMP instructions. As the instruction no longer computes a
subtraction, we can't use it for variable locations.
Differential Revision: https://reviews.llvm.org/D88898
Added in 47c3fe2a22, we sometimes need to describe a variable value
substitution with a subregister qualifier, to say that "the value is the
lower 32 bits of this 64 bit register def" for example. That then needs
support during LiveDebugValues to interpret the subregister qualifiers,
which is what this patch adds.
Whenever we encounter a DBG_INSTR_REF and find its value by using a
substitution, collect any subregister qualifiers seen. Then, accumulate the
effects of the qualifiers to work out what offset and what size should be
extracted from the defined register. Finally, for the target ValueIDNum,
extract whatever subregister is in the correct position
Currently, describing a subregister field of a larger value that has been
spilt to the stack, is unimplemented.
Differential Revision: https://reviews.llvm.org/D88894
Very late in compilation, backends like X86 will perform optimisations like
this:
$cx = MOV16rm $rax, ...
->
$rcx = MOV64rm $rax, ...
Widening the load from 16 bits to 64 bits. SEeing how the lower 16 bits
remain the same, this doesn't affect execution. However, any debug
instruction reference to the defined operand now refers to a 64 bit value,
nto a 16 bit one, which might be unexpected. Elsewhere in codegen, there's
often this pattern:
CALL64pcrel32 @foo, implicit-def $rax
%0:gr64 = COPY $rax
%1:gr32 = COPY %0.sub_32bit
Where we want to refer to the definition of $eax by the call, but don't
want to refer the copies (they don't define values in the way
LiveDebugValues sees it). To solve this, add a subregister field to the
existing "substitutions" facility, so that we can describe a field within
a larger value definition. I would imagine that this would be used most
often when a value is widened, and we need to refer to the original,
narrower definition.
Differential Revision: https://reviews.llvm.org/D88891
In various circumstances, when we clobber a register there may be
alternative locations that the value is live in. The classic example would
be a value loaded from the stack, and then clobbered: the value is still
available on the stack. InstrRefBasedLDV was coping with this at block
starts where it's forced to pick a location, however it wasn't searching
for alternative locations when values were clobbered.
This patch notifies the "Transfer Tracker" object when clobbers occur, and
it's able to find alternatives and issue DBG_VALUEs for that location. See:
the added test.
Differential Revision: https://reviews.llvm.org/D88405
This patch reads machine value numbers from DBG_PHI instructions (marking
where SSA PHIs used to be), and matches them up with DBG_INSTR_REF
instructions that refer to them. Essentially they are two separate parts of
a DBG_VALUE: the place to read the value (register and program position),
and where the variable is assigned that value.
Sometimes these DBG_PHIs can be duplicated, usually by tail duplication.
This corresponds to the SSA structure of the program being destroyed, and
the original PHI being split. When this happens: run LLVMs standard
SSAUpdater utility, to work out what values should appear in which blocks.
The majority of this patch is boilerplate to make use of SSAUpdater.
If there are any additional PHIs on the path between multiple DBG_PHIs and
their using DBG_INSTR_REF, their existance is validated, just in case a
value gets clobbered along the way (see dbg-phis-with-loops.mir for
several examples).
Differential Revision: https://reviews.llvm.org/D86814
Was reverted in 0507fc2ffc, in phi-coalesce-subreg.mir I'd explicitly named
some passes to run instead of specifying a range. As a result some
two-address-instrs weren't correctly rewritten and the verifier got upset.
Original commit message:
[DebugInstrRef][2/3] Track PHI values through register coalescing
In the instruction referencing variable location model, we store variable
locations that point at PHIs in MachineFunction during register allocation.
Unfortunately, register coalescing can substantially change the locations
of registers, and so that PHI-variable-location side table needs
maintenence during the pass.
This patch builds an index from the side table, and whenever a vreg gets
coalesced into another vreg, update the index to record the new vreg that
the PHI happens in. It also accepts a limited range of subregister
coalescing, for example merging a subregister into a larger class.
Differential Revision: https://reviews.llvm.org/D86813
In the instruction referencing variable location model, we store variable
locations that point at PHIs in MachineFunction during register
allocation. Unfortunately, register coalescing can substantially change
the locations of registers, and so that PHI-variable-location side table
needs maintenence during the pass.
This patch builds an index from the side table, and whenever a vreg gets
coalesced into another vreg, update the index to record the new vreg that
the PHI happens in. It also accepts a limited range of subregister
coalescing, for example merging a subregister into a larger class.
Differential Revision: https://reviews.llvm.org/D86813
This patch introduces "DBG_PHI" instructions, a marker of where a PHI
instruction used to be, before PHI elimination. Under the instruction
referencing model, we want to know where every value in the function is
defined -- and a PHI, even if implicit, is such a place.
Just like instruction numbers, we can use this to identify a value to be
used as a variable value, but we don't need to know what instruction
defines that value, for example:
bb1:
DBG_PHI $rax, 1
[... more insts ... ]
bb2:
DBG_INSTR_REF 1, 0, !1234, !DIExpression()
This specifies that on entry to bb1, whatever value is in $rax is known
as value number one -- and the later DBG_INSTR_REF marks the position
where variable !1234 should take on value number one.
PHI locations are stored in MachineFunction for the duration of the
regalloc phase in the DebugPHIPositions map. The map is populated by
PHIElimination, and then flushed back into the instruction stream by
virtregrewriter. A small amount of maintenence is needed in
LiveDebugVariables to account for registers being split, but only for
individual positions, not for entire ranges of blocks.
Differential Revision: https://reviews.llvm.org/D86812
Deciding where to place debugging instructions when normal instructions
sink between blocks is difficult -- see PR44117. Dealing with this with
instruction-referencing variable locations is simple: we just tolerate
DBG_INSTR_REFs referring to values that haven't been computed yet. This
patch adds support into InstrRefBasedLDV to record when a variable value
appears in the middle of a block, and should have a DBG_VALUE added when it
appears (a debug use before def).
While described simply, this relies heavily on the value-propagation
algorithm in InstrRefBasedLDV. The implementation doesn't attempt to verify
the location of a value unless something non-trivial occurs to merge
variable values in vlocJoin. This means that a variable with a value that
has no location can retain it across all control flow (including loops).
It's only when another debug instruction specifies a different variable
value that we have to check, and find there's no location.
This property means that if a machine value is defined in a block dominated
by a DBG_INSTR_REF that refers to it, all the successor blocks can
automatically find a location for that value (if it's not clobbered). Thus
in a sense, InstrRefBasedLDV is already supporting and implementing
use-before-defs. This patch allows us to specify a variable location in the
block where it's defined.
When loading live-in variable locations, TransferTracker currently discards
those where it can't find a location for the variable value. However, we
can tell from the machine value number whether the value is defined in this
block. If it is, add it to a set of use-before-def records. Then, once the
relevant instruction has been processed, emit a DBG_VALUE immediately after
it.
Differential Revision: https://reviews.llvm.org/D85775
Handle DBG_INSTR_REF instructions in LiveDebugValues, to determine and
propagate variable locations. The logic is fairly straight forwards:
Collect a map of debug-instruction-number to the machine value numbers
generated in the first walk through the function. When building the
variable value transfer function and we see a DBG_INSTR_REF, look up the
instruction it refers to, and pick the machine value number it generates,
That's it; the rest of LiveDebugValues continues as normal.
Awkwardly, there are two kinds of instruction numbering happening here: the
offset into the block (which is how machine value numbers are determined),
and the numbers that we label instructions with when generating
DBG_INSTR_REFs.
I've also restructured the TransferTracker redefVar code a little, to
separate some DBG_VALUE specific operations into its own method. The
changes around redefVar should be largely NFC, while allowing
DBG_INSTR_REFs to specify a value number rather than just a location.
Differential Revision: https://reviews.llvm.org/D85771
Both FastRegAlloc and LiveDebugVariables/greedy need to cope with
DBG_INSTR_REFs. None of them actually need to take any action, other than
passing DBG_INSTR_REFs through: variable location information doesn't refer
to any registers at this stage.
LiveDebugVariables stashes the instruction information in a tuple, then
re-creates it later. This is only necessary as the register allocator
doesn't expect to see any debug instructions while it's working. No
equivalence classes or interval splitting is required at all!
No changes are needed for the fast register allocator, as it just ignores
debug instructions. The test added checks that both of them preserve
DBG_INSTR_REFs.
This also expands ScheduleDAGInstrs.cpp to treat DBG_INSTR_REFs the same as
DBG_VALUEs when rescheduling instructions around. The current movement of
DBG_VALUEs around is less than ideal, but it's not a regression to make
DBG_INSTR_REFs subject to the same movement.
Differential Revision: https://reviews.llvm.org/D85757
The instruction referencing work currently only works on X86, and all the
tests for it will be X86 based for the time being. Configure the whole
directory to be X86-only, seeing how I keep on landing tests that don't
have the correct REQUIRES lines.
This patch touches two optimizations, TwoAddressInstruction and X86's
FixupLEAs pass, both of which optimize by re-creating instructions. For
LEAs, various bits of arithmetic are better represented as LEAs on X86,
while TwoAddressInstruction sometimes converts instrs into three address
instructions if it's profitable.
For debug instruction referencing, both of these require substitutions to
be created -- the old instruction number must be pointed to the new
instruction number, as illustrated in the added test. If this isn't done,
any variable locations based on the optimized instruction are
conservatively dropped.
Differential Revision: https://reviews.llvm.org/D85756
Add a table recording "substitutions" between pairs of <instruction,
operand> numbers, from old pairs to new pairs. Post-isel optimizations are
able to record the outcome of an optimization in this way. For example, if
there were a divide instruction that generated the quotient and remainder,
and it were replaced by one that only generated the quotient:
$rax, $rcx = DIV-AND-REMAINDER $rdx, $rsi, debug-instr-num 1
DBG_INSTR_REF 1, 0
DBG_INSTR_REF 1, 1
Became:
$rax = DIV $rdx, $rsi, debug-instr-num 2
DBG_INSTR_REF 1, 0
DBG_INSTR_REF 1, 1
We could enter a substitution from <1, 0> to <2, 0>, and no substitution
for <1, 1> as it's no longer generated.
This approach means that if an instruction or value is deleted once we've
left SSA form, all variables that used the value implicitly become
"optimized out", something that isn't true of the current DBG_VALUE
approach.
Differential Revision: https://reviews.llvm.org/D85749
Jeremy Morse