[DebugInfo][InstrRef] Preserve properties of restored variables

InstrRefBasedLDV observes when variable locations are clobbered, scans what
values are available in the machine, and re-issues a DBG_V

[DebugInfo][InstrRef] Preserve properties of restored variables

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

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[DebugInfo][InstrRef] Add extra indirection for NRVO tests

In some scenarios, usually involving NRVO, we can issue indirect DBG_VALUEs
after SelectionDAG, even in instruction referencing mode (if th

[DebugInfo][InstrRef] Add extra indirection for NRVO tests

In some scenarios, usually involving NRVO, we can issue indirect DBG_VALUEs
after SelectionDAG, even in instruction referencing mode (if the variable
is an argument). If the corresponding argument value is spilt to the stack,
then we have:
* Indirection from it being on the stack,
* Indirection from it being a dbg.declare or a dbg.addr.

However InstrRefBasedLDV only emits one level of indirection. This patch
adds the second, by adding an extra DW_OP_deref if necessary. The two
tests modified fail otherwise -- they feature some NRVO, and require two
levels of indirection to be correct.

Differential Revision: https://reviews.llvm.org/D114364

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[DebugInfo][InstrRef] Track variable assignments in out-of-scope blocks

DBG_INSTR_REF's and DBG_VALUE's can end up in blocks that aren't in the
lexical scope of their variable. It's arguable as to

[DebugInfo][InstrRef] Track variable assignments in out-of-scope blocks

DBG_INSTR_REF's and DBG_VALUE's can end up in blocks that aren't in the
lexical scope of their variable. It's arguable as to what we should do
about this, however VarLocBasedLDV permits such variable locations to be
propagated, so let's allow it in InstrRefBasedLDV.

It's necessary for the modified test to work.

Differential Revision: https://reviews.llvm.org/D114578

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[DebugInfo][InstrRef] Cope with win32 calls changing SP in LiveDebugValues

Almost all of the time, call instructions don't actually lead to SP being
different after they return. An exception is win3

[DebugInfo][InstrRef] Cope with win32 calls changing SP in LiveDebugValues

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

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[DebugInfo][InstrRef] Ignore SP clobbers on call instructions even more

Avoid un-necessarily recreating DBG_VALUEs on call instructions.

In LiveDebugvalues we choose to ignore any clobbers of SP by

[DebugInfo][InstrRef] Ignore SP clobbers on call instructions even more

Avoid un-necessarily recreating DBG_VALUEs on call instructions.

In LiveDebugvalues we choose to ignore any clobbers of SP by call
instructions, as they're irrelevant to our model of the machine. We
currently do so for tracking register values (MTracker); do the same for
tracking variable locations (TTracker).

Test modified to endure that a duplicate DBG_VALUE is not created after the
call in struction in this test.

Differential Revision: https://reviews.llvm.org/D114365

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[llvm] Use MachineBasicBlock::{successors,predecessors} (NFC)

[DebugInfo][InstrRef][NFC] Switch to using DenseMaps and similar

There are a few STL containers hanging around that can become DenseMaps,
SmallVectors and similar. This recovers a modest amount of c

[DebugInfo][InstrRef][NFC] Switch to using DenseMaps and similar

There are a few STL containers hanging around that can become DenseMaps,
SmallVectors and similar. This recovers a modest amount of compile time
performance.

While I'm here, adjust the bit layout of ValueIDNum: this was always
supposed to act like a value type, however it seems that clang doesn't
compile the comparison functions to act that way. Add a uint64_t to a
union that explicitly aliases the bitfields, so that we can compare the
whole value as a single integer.

Differential Revision: https://reviews.llvm.org/D112333

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[DebugInfo][InstrRef] Recover stack-slot tracking performance

This patch is like D111627 -- instead of calculating IDF for every location
on the stack, only do it for the smallest units of interfere

[DebugInfo][InstrRef] Recover stack-slot tracking performance

This patch is like D111627 -- instead of calculating IDF for every location
on the stack, only do it for the smallest units of interference, and copy
the PHIs for those units to any aliases.

The test added runs placeMLocPHIs directly, and tests that:
* A def of the lower 8 bits of a stack slot causes all aliasing regs to
have PHIs placed,
* It doesn't cause the equivalent location to x86's $ah, which isn't
aliased, to have a PHI placed.

Differential Revision: https://reviews.llvm.org/D112324

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[DebugInfo][InstrRef] Track values fused into stack spills

During register allocation, some instructions can have stack spills fused
into them. It means that when vregs are allocated on the stack we

[DebugInfo][InstrRef] Track values fused into stack spills

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

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[DebugInfo][NFC] Avoid a use-after-free

This patch swaps two lines -- the CurSucc reference can be invalidated
by the call to DFS.push_back, therefore that should happen last. The
usual hat-tip to a

[DebugInfo][NFC] Avoid a use-after-free

This patch swaps two lines -- the CurSucc reference can be invalidated
by the call to DFS.push_back, therefore that should happen last. The
usual hat-tip to asan for catching this.

This patch also swaps an ealier call to ToAdd.insert and DFS.push_back,
where a stable iterator (from successors()) is being used. This isn't
strictly necessary, but is good for consistency and avoiding readers
asking themselves why the two code portions have a different order.

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[DebugInfo][Instr] Track subregisters across stack spills/restores

Sometimes we generate code that writes to a subregister, then spills /
restores a super-register to the stack, for example:

$e

[DebugInfo][Instr] Track subregisters across stack spills/restores

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

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[DebugInfo][InstrRef] Add unit tests for transfer-function building

This patch adds some unit tests for the machine-location transfer-function
building parts of InstrRefBasedLDV: i.e., test that if

[DebugInfo][InstrRef] Add unit tests for transfer-function building

This patch adds some unit tests for the machine-location transfer-function
building parts of InstrRefBasedLDV: i.e., test that if we feed some MIR
into the transfer-function building code, does it create the correct
transfer function.

There are a number of minor defects that get corrected in the process:
* The unit test was selecting the x86 (i.e. 32 bit) backend rather than
x86_64's 64 bit backend,
* COPY instructions weren't actually having their subregister values
correctly represented in the transfer function. Subregisters were being
defined by the COPY, rather than taking the value in the source register.
* SP aliases were at risk of being clobbered, if an SP subregister was
clobbered.

Differential Revision: https://reviews.llvm.org/D112006

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[DebugInfo][InstrRef] Track a single variable at a time

Here's another performance patch for InstrRefBasedLDV: rather than
processing all variable values in a scope at a time, instead, process one
v

[DebugInfo][InstrRef] Track a single variable at a time

Here's another performance patch for InstrRefBasedLDV: rather than
processing all variable values in a scope at a time, instead, process one
variable at a time. The benefits are twofold:
* It's easier to reason about one variable at a time in your mind,
* It improves performance, apparently from increased locality.

The downside is that the value-propagation code gets indented one level
further, plus there's some churn in the unit tests.

Differential Revision: https://reviews.llvm.org/D111799

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[DebugInfo][InstrRef] Avoid un-necessary densemap copies and comparisons

This is purely a performance patch: InstrRefBasedLDV used to use three
DenseMaps to store variable values, two for long term

[DebugInfo][InstrRef] Avoid un-necessary densemap copies and comparisons

This is purely a performance patch: InstrRefBasedLDV used to use three
DenseMaps to store variable values, two for long term storage and one as a
working set. This patch eliminates the working set, and updates the long
term storage in place, thus avoiding two DenseMap comparisons and two
DenseMap assignments, which can be expensive.

Differential Revision: https://reviews.llvm.org/D111716

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Fix signed/unsigned comparison after b5426ced71280

gcc11 warns that this counter causes a signed/unsigned comaprison when it's
later compared with a SmallVector::difference_type. gcc appears to be
c

Fix signed/unsigned comparison after b5426ced71280

gcc11 warns that this counter causes a signed/unsigned comaprison when it's
later compared with a SmallVector::difference_type. gcc appears to be
correct, clang does not warn one way or the other.

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[DebugInfo][InstrRef] Place variable-values PHI using LLVM utilities

This patch is very similar to D110173 / a3936a6c19c, but for variable
values rather than machine values. This is for the second i

[DebugInfo][InstrRef] Place variable-values PHI using LLVM utilities

This patch is very similar to D110173 / a3936a6c19c, 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

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[DebugInfo][InstrRef] Only calculate IDF for reg units

In D110173 we start using the existing LLVM IDF calculator to place PHIs as
we reconstruct an SSA form of machine-code program. Sadly that's sl

[DebugInfo][InstrRef] Only calculate IDF for reg units

In D110173 we start using the existing LLVM IDF calculator to place PHIs as
we reconstruct an SSA form of machine-code program. Sadly that's slower
than the old (but broken) way, this patch attempts to recover some of that
performance.

The key observation: every time we def a register, we also have to def it's
register units. If we def'd $rax, in the current implementation we
independently calculate PHI locations for {al, ah, ax, eax, hax, rax}, and
they will all have the same PHI positions. Instead of doing that, we can
calculate the PHI positions for {al, ah} and place PHIs for any aliasing
registers in the same positions. Any def of a super-register has to def
the unit, and vice versa, so this is sound. It cuts down the SSA placement
we need to do significantly.

This doesn't work for stack slots, or registers we only ever read, so place
PHIs normally for those. LiveDebugValues choses to ignore writes to SP at
calls, and now have to ignore writes to SP register units too.

Differential Revision: https://reviews.llvm.org/D111627

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Follow up a3936a6c19c to work around an old compiler bug

Old versions of gcc want template specialisations to happen within the
namespace where the template lives; this is still present in gcc 5.1,

Follow up a3936a6c19c to work around an old compiler bug

Old versions of gcc want template specialisations to happen within the
namespace where the template lives; this is still present in gcc 5.1, which
we officially support, so it has to be worked around.

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[DebugInfo][InstrRef] Use PHI placement utilities for machine locations

InstrRefBasedLDV used to try and determine which values are in which
registers using a lattice approach; however this is hard

[DebugInfo][InstrRef] Use PHI placement utilities for machine locations

InstrRefBasedLDV used to try and determine which values are in which
registers using a lattice approach; however this is hard to understand, and
broken in various ways. This patch replaces that approach with a standard
SSA approach using existing LLVM utilities. PHIs are placed at dominance
frontiers; value propagation then eliminates un-necessary PHIs.

This patch also adds a bunch of unit tests that should cover many of the
weirder forms of control flow.

Differential Revision: https://reviews.llvm.org/D110173

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Scatter NDEBUG to fix after 838b4a533e6

These "dump" methods call into MachineOperand::dump, which doesn't exist
with NDEBUG, thus we croak. Disable LiveDebugValues dump methods when
NDEBUG is turne

Scatter NDEBUG to fix after 838b4a533e6

These "dump" methods call into MachineOperand::dump, which doesn't exist
with NDEBUG, thus we croak. Disable LiveDebugValues dump methods when
NDEBUG is turned on to avoid this.

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[DebugInfo][NFC] Move LiveDebugValues class to header

This patch shifts the InstrRefBasedLDV class declaration to a header.
Partially because it's already massive, but mostly so that I can start
wri

[DebugInfo][NFC] Move LiveDebugValues class to header

This patch shifts the InstrRefBasedLDV class declaration to a header.
Partially because it's already massive, but mostly so that I can start
writing some unit tests for it. This patch also adds the boilerplate for
said unit tests.

Differential Revision: https://reviews.llvm.org/D110165

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[MachineInstr] Move MIParser's DBG_VALUE RegState::Debug invariant into MachineInstr::addOperand

Based on the reasoning of D53903, register operands of DBG_VALUE are
invariably treated as RegState::

[MachineInstr] Move MIParser's DBG_VALUE RegState::Debug invariant into MachineInstr::addOperand

Based on the reasoning of D53903, register operands of DBG_VALUE are
invariably treated as RegState::Debug operands. This change enforces
this invariant as part of MachineInstr::addOperand so that all passes
emit this flag consistently.

RegState::Debug is inconsistently set on DBG_VALUE registers throughout
LLVM. This runs the risk of a filtering iterator like
MachineRegisterInfo::reg_nodbg_iterator to process these operands
erroneously when not parsed from MIR sources.

This issue was observed in the development of the llvm-mos fork which
adds a backend that relies on physical register operands much more than
existing targets. Physical RegUnit 0 has the same numeric encoding as
$noreg (indicating an undef for DBG_VALUE). Allowing debug operands into
the machine scheduler correlates $noreg with RegUnit 0 (i.e. a collision
of register numbers with different zero semantics). Eventually, this
causes an assert where DBG_VALUE instructions are prohibited from
participating in live register ranges.

Reviewed By: MatzeB, StephenTozer

Differential Revision: https://reviews.llvm.org/D110105

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[DebugInfo][InstrRef] Track all of DBG_PHIs operands

An important part of the instruction referencing solution is that we
identify all the registers that values move between before we then compute
a

[DebugInfo][InstrRef] Track all of DBG_PHIs operands

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

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[DebugInfo][InstrRef] Correctly ignore DBG_VALUE_LIST in InstrRef mode

This patch makes InstrRefBasedLDV "safe" to work with DBG_VALUE_LISTs. It
doesn't actually interpret them, but it recognises th

[DebugInfo][InstrRef] Correctly ignore DBG_VALUE_LIST in InstrRef mode

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

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[DebugInfo][InstrRef] Remove a faulty assertion

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 machin

[DebugInfo][InstrRef] Remove a faulty assertion

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

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