Commit Graph

42784 Commits

Author SHA1 Message Date
Sam McCall 128ce70eef [CodeCompletion] Avoid spurious signature help for init-list args
Somewhat surprisingly, signature help is emitted as a side-effect of
computing the expected type of a function argument.
The reason is that both actions require enumerating the possible
function signatures and running partial overload resolution, and doing
this twice would be wasteful and complicated.

Change #1: document this, it's subtle :-)

However, sometimes we need to compute the expected type without having
reached the code completion cursor yet - in particular to allow
completion of designators.
eb4ab3358c did this but introduced a
regression - it emits signature help in the wrong location as a side-effect.

Change #2: only emit signature help if the code completion cursor was reached.

Currently there is PP.isCodeCompletionReached(), but we can't use it
because it's set *after* running code completion.
It'd be nice to set this implicitly when the completion token is lexed,
but ConsumeCodeCompletionToken() makes this complicated.

Change #3: call cutOffParsing() *first* when seeing a completion token.

After this, the fact that the Sema::Produce*SignatureHelp() functions
are even more confusing, as they only sometimes do that.
I don't want to rename them in this patch as it's another large
mechanical change, but we should soon.

Change #4: prepare to rename ProduceSignatureHelp() to GuessArgumentType() etc.

Differential Revision: https://reviews.llvm.org/D98488
2021-03-16 12:46:40 +01:00
Pushpinder Singh fc12a64ecc [OpenMP][AMDGPU] Skip backend and assemble phases for amdgcn
Remove emit-llvm-bc from addClangTargetOptions as it conflicts with -E for save-temps.

AMDGCN does not yet support linking object files so backend and assemble actions are
skipped, leaving LLVM IR as the output format.

Reviewed By: JonChesterfield, ronlieb

Differential Revision: https://reviews.llvm.org/D96769
2021-03-16 04:58:14 +00:00
Amy Huang f5352dd9da Emit inline implementation of __builtin__wmemchr on MSVCRT platforms.
The MSVC runtime library doesn't have a definition for wmemchr,
so provide an inline implementation.

Differential Revision: https://reviews.llvm.org/D98472
2021-03-15 15:30:55 -07:00
diggerlin d1f1bff81b [AIX][XCOFF] Fixed the test case which failed at aix OS because enable -mignore-xcoff-visibility by default.
Summary:

because we enable -mignore-xcoff-visibility by default when there is no -fvisibility option in the clang in AIX OS
it will cause some test case fail at aix os. in order to let the -mignore-xcoff-visibility to be disable, we need to add the -fvisibility=default for those test case.

Reviewers: hubert.reinterpretcast daltenty
Differential Revision: https://reviews.llvm.org/D98660
2021-03-15 17:33:02 -04:00
Jonas Paulsson 9cfd301ec8 [SystemZ] Test for isinf and isfinite in testFPKind().
Recognize BI__builtin_isinf and BI__builtin_isfinite (and a few other opcodes
for finite) in testFPKind() and handle with TDC.

Review: Ulrich Weigand.

Differential Revision: https://reviews.llvm.org/D97901
2021-03-15 15:02:39 -06:00
Stefan Pintilie 86f2a3d178 [PowerPC] Add __PCREL__ when PC Relative is enabled.
This patch adds the `__PCREL__` define when PC Relative addressing is enabled.

Reviewed By: nemanjai, #powerpc

Differential Revision: https://reviews.llvm.org/D98546
2021-03-15 15:13:02 -05:00
Markus Böck af2796c76d [test] Add ability to get error messages from CMake for errc substitution
Visual Studios implementation of the C++ Standard Library does not use strerror to produce a message for std::error_code unlike other standard libraries such as libstdc++ or libc++ that might be used.

This patch adds a cmake script that through running a C++ program gets the error messages for the POSIX error codes and passes them onto lit through an optional config parameter.

If the config parameter is not set, or getting the messages failed, due to say a cross compiling configuration without an emulator, it will fall back to using pythons strerror functions.

Differential Revision: https://reviews.llvm.org/D98278
2021-03-15 20:56:08 +01:00
Stelios Ioannou ab86edbc88 [AArch64] Implement __rndr, __rndrrs intrinsics
This patch implements the __rndr and __rndrrs intrinsics to provide access to the random
number instructions introduced in Armv8.5-A. They are only defined for the AArch64
execution state and are available when __ARM_FEATURE_RNG is defined.

These intrinsics store the random number in their pointer argument and return a status
code if the generation succeeded. The difference between __rndr __rndrrs, is that the latter
intrinsic reseeds the random number generator.

The instructions write the NZCV flags indicating the success of the operation that we can
then read with a CSET.

[1] https://developer.arm.com/docs/101028/latest/data-processing-intrinsics
[2] https://bugs.llvm.org/show_bug.cgi?id=47838

Differential Revision: https://reviews.llvm.org/D98264

Change-Id: I8f92e7bf5b450e5da3e59943b53482edf0df6efc
2021-03-15 17:51:48 +00:00
serge-sans-paille 4aa510be78 Allow __ieee128 as an alias to __float128 on ppc
This matches gcc behavior.

Differential Revision: https://reviews.llvm.org/D97846
2021-03-15 18:28:26 +01:00
Luke Drummond fcfd3fda71 [OpenCL] Respect calling convention for builtin
`__translate_sampler_initializer` has a calling convention of
`spir_func`, but clang generated calls to it using the default CC.

Instruction Combining was lowering these mismatching calling conventions
to `store i1* undef` which itself was subsequently lowered to a trap
instruction by simplifyCFG resulting in runtime `SIGILL`

There are arguably two bugs here: but whether there's any wisdom in
converting an obviously invalid call into a runtime crash over aborting
with a sensible error message will require further discussion. So for
now it's enough to set the right calling convention on the runtime
helper.

Reviewed By: svenh, bader

Differential Revision: https://reviews.llvm.org/D98411
2021-03-15 17:26:51 +00:00
Melanie Blower 33b1f3f42c [clang][patch] Solve PR49479, File scope fp pragma should propagate to functions nested in struct, and initialization expressions
Previously, the CurFPFeatures state was set to command line settings before
semantic analysis of the nested member functions and initialization
expressions, that's not correct, it should use the pragma state which
is in effect at the lexical position.

Reviewed By: Erich Keane, Aaron Ballman

Differential Revision: https://reviews.llvm.org/D98211
2021-03-15 12:15:20 -04:00
Thomas Preud'homme f60b35340f Stop traping on sNaN in __builtin_isinf
__builtin_isinf currently generates a floating-point compare operation
which triggers a trap when faced with a signaling NaN in StrictFP mode.
This commit uses integer operations instead to not generate any trap in
such a case.

Reviewed By: mibintc

Differential Revision: https://reviews.llvm.org/D97125
2021-03-15 15:38:08 +00:00
David Green 2b3c813143 [Clang][ARM] Reenable arm_acle.c test.
This test was apparently disabled in 6fcd4e080f, without any
sign of how it was going to be reenabled. This patch rewrites the test
to use update_cc_test_checks, with midend optimizations other that
mem2reg disabled.

The first attempt of this patch in 5ae949a927 failed on bots even
though it worked locally.  I've attempted to adjust the RUN lines and
made the test AArch64/ARM specific.

Differential Revision: https://reviews.llvm.org/D98510
2021-03-14 10:59:24 +00:00
Giorgis Georgakoudis 1ce846be04 Replace func name with regex for update test scripts
The patch adds an argument to update test scripts, such as update_cc_test_checks, for replacing a function name matching a regex. This functionality is needed to match generated function signatures that include file hashes. Example:

The function signature for the following function:

`__omp_offloading_50_b84c41e__Z9ftemplateIiET_i_l30_worker`

with `--replace-function-regex "__omp_offloading_[0-9]+_[a-z0-9]+_(.*)"` will become:

`CHECK-LABEL: @{{__omp_offloading_[0-9]+_[a-z0-9]+__Z9ftemplateIiET_i_l30_worker}}(`

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D97107
2021-03-12 17:37:09 -08:00
Giorgis Georgakoudis 9f9a4dfda7 Revert "Replace func name with regex for update test scripts"
This reverts commit 5eaf70afb5.
2021-03-12 17:20:00 -08:00
Giorgis Georgakoudis 5eaf70afb5 Replace func name with regex for update test scripts
The patch adds an argument to update test scripts, such as update_cc_test_checks, for replacing a function name matching a regex. This functionality is needed to match generated function signatures that include file hashes. Example:

The function signature for the following function:

`__omp_offloading_50_b84c41e__Z9ftemplateIiET_i_l30_worker`

with `--replace-function-regex "__omp_offloading_[0-9]+_[a-z0-9]+_(.*)"` will become:

`CHECK-LABEL: @{{__omp_offloading_[0-9]+_[a-z0-9]+__Z9ftemplateIiET_i_l30_worker}}(`

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D97107
2021-03-12 17:00:42 -08:00
Matheus Izvekov d4a8c7359b [clang] Fix ICE on invalid type parameters for concepts
See PR48593.

Constraints with invalid type parameters were causing a null pointer
dereference.

Signed-off-by: Matheus Izvekov <mizvekov@gmail.com>

Reviewed By: rsmith

Differential Revision: https://reviews.llvm.org/D98095
2021-03-13 01:23:02 +01:00
Matheus Izvekov c9fd92d573 [clang] Improve diagnostics on implicitly deleted defaulted comparisons
This patch just makes the error message clearer by reinforcing the cause
was a lack of viable **three-way** comparison function for the
**complete object**.

Signed-off-by: Matheus Izvekov <mizvekov@gmail.com>

Reviewed By: rsmith

Differential Revision: https://reviews.llvm.org/D97990
2021-03-13 01:13:52 +01:00
Amy Huang d7cd208f08 [DebugInfo] Add an attribute to force type info to be emitted for types that are required to be complete.
This was motivated by the fact that constructor type homing (debug info
optimization that we want to turn on by default) drops some libc++ types,
so an attribute would allow us to override constructor homing and emit
them anyway. I'm currently looking into the particular libc++ issue, but
even if we do fix that, this issue might come up elsewhere and it might be
nice to have this.

As I've implemented it now, the attribute isn't specific to the
constructor homing optimization and overrides all of the debug info
optimizations.

Open to discussion about naming, specifics on what the attribute should do, etc.

Differential Revision: https://reviews.llvm.org/D97411
2021-03-12 12:30:01 -08:00
Anastasia Stulova eed88e91f3 [OpenCL] Use spir target for CIndex tests for OpenCL.
This fixes failing bots.

Patch by azabaznov (Anton Zabaznov)!

Differential Revision: https://reviews.llvm.org/D98539
2021-03-12 20:11:26 +00:00
Nico Weber d7b7e2026b Revert "[Clang][ARM] Reenable arm_acle.c test."
This reverts commit 5ae949a927.
Test fails everywhere.
2021-03-12 14:37:37 -05:00
David Green 5ae949a927 [Clang][ARM] Reenable arm_acle.c test.
This test was apparently disabled in 6fcd4e080f, without any
sign of how it was going to be reenabled. This patch rewrites the test
to use update_cc_test_checks, with midend optimizations other that
mem2reg disabled.
2021-03-12 19:21:21 +00:00
Nemanja Ivanovic b5fae4b9b2 [PowerPC] Add more missing overloads to altivec.h
We are missing more predicate forms for 'vector double' and some
tests. This adds the missing overloads and completes the set of
test cases for them.
2021-03-12 10:51:57 -06:00
Valeriy Savchenko 6dc1523508 [analyzer][solver] Prevent infeasible states (PR49490)
This patch fixes the situation when our knowledge of disequalities
can help us figuring out that some assumption is infeasible, but
the solver still produces a state with inconsistent constraints.

Additionally, this patch adds a couple of assertions to catch this
type of problems easier.

Differential Revision: https://reviews.llvm.org/D98341
2021-03-12 15:56:48 +03:00
Hans Wennborg f50aef745c Revert "[InstrProfiling] Don't generate __llvm_profile_runtime_user"
This broke the check-profile tests on Mac, see comment on the code
review.

> This is no longer needed, we can add __llvm_profile_runtime directly
> to llvm.compiler.used or llvm.used to achieve the same effect.
>
> Differential Revision: https://reviews.llvm.org/D98325

This reverts commit c7712087cb.

Also reverting the dependent follow-up commit:

Revert "[InstrProfiling] Generate runtime hook for ELF platforms"

> When using -fprofile-list to selectively apply instrumentation only
> to certain files or functions, we may end up with a binary that doesn't
> have any counters in the case where no files were selected. However,
> because on Linux and Fuchsia, we pass -u__llvm_profile_runtime, the
> runtime would still be pulled in and incur some non-trivial overhead,
> especially in the case when the continuous or runtime counter relocation
> mode is being used. A better way would be to pull in the profile runtime
> only when needed by declaring the __llvm_profile_runtime symbol in the
> translation unit only when needed.
>
> This approach was already used prior to 9a041a7522, but we changed it
> to always generate the __llvm_profile_runtime due to a TAPI limitation.
> Since TAPI is only used on Mach-O platforms, we could use the early
> emission of __llvm_profile_runtime there, and on other platforms we
> could change back to the earlier approach where the symbol is generated
> later only when needed. We can stop passing -u__llvm_profile_runtime to
> the linker on Linux and Fuchsia since the generated undefined symbol in
> each translation unit that needed it serves the same purpose.
>
> Differential Revision: https://reviews.llvm.org/D98061

This reverts commit 87fd09b25f.
2021-03-12 13:53:46 +01:00
Aaron Ballman e448310059 Add support for digit separators in C2x.
WG14 adopted N2626 at the meetings this week. This commit adds support
for using ' as a digit separator in a numeric literal which is
compatible with the C++ feature.
2021-03-12 07:21:03 -05:00
Anton Zabaznov 840643bbe1 [OpenCL] Refactor diagnostic for OpenCL extension/feature
There is no need to check for enabled pragma for core or optional core features,
thus this check is removed

Reviewed By: Anastasia

Differential Revision: https://reviews.llvm.org/D97058
2021-03-12 11:43:53 +03:00
Johannes Doerfert 49ed3032ff Revert "[OpenMP] Do not propagate match extensions to nested contexts"
Two tests failed for some reason, need to investigate:
  https://lab.llvm.org/buildbot/#/builders/109/builds/10399

This reverts commit ad9e98b8ef.
2021-03-11 23:48:36 -06:00
Johannes Doerfert 0fe0d114e4 Revert "[OpenMP] Introduce the `disable_selector_propagation` variant selector trait"
Need to revert ad9e98b8ef which this
commit depends on.

This reverts commit f771ef7b5f0ed260d00931cd50e6fe462edbacaf.
2021-03-11 23:48:35 -06:00
Johannes Doerfert b2642456ab [OpenMP] Introduce the `disable_selector_propagation` variant selector trait
Nested `omp [begin|end] declare variant` inherit the selectors from
surrounding `omp (begin|end) declare variant` constructs. To stop such
propagation the user can add the `disable_selector_propagation` to the
`extension` set in the `implementation` selector.

Reviewed By: tianshilei1992

Differential Revision: https://reviews.llvm.org/D95765
2021-03-11 23:31:25 -06:00
Johannes Doerfert ad9e98b8ef [OpenMP] Do not propagate match extensions to nested contexts
If we have nested declare variant context, it doesn't make sense to
inherit the match extension from the parent. Instead, just skip it.

Reviewed By: JonChesterfield

Differential Revision: https://reviews.llvm.org/D95764
2021-03-11 23:31:21 -06:00
Johannes Doerfert cd1bd6e587 [Utils] Check for more global information in update_test_checks
This allows to check for various globals (metadata/attributes/...) and
also resolves problems with globals (metadata/attributes/...) being
reused across different prefixes.

Reviewed By: sstefan1

Differential Revision: https://reviews.llvm.org/D94741
2021-03-11 23:31:16 -06:00
Sriraman Tallam cdb42a4cc4 Disable unique linkage suffixes ifor global vars until demanglers can be fixed.
D96109 added support for unique internal linkage names for both internal
linkage functions and global variables. There was a lot of discussion on how to
get the demangling right for functions but I completely missed the point that
demanglers do not support suffixes for global vars. For example:

$ c++filt _ZL3foo
foo
$ c++filt _ZL3foo.uniq.123
_ZL3foo.uniq.123

The demangling for functions works as expected.

I am not sure of the impact of this. I don't understand how debuggers and other
tools depend on the correctness of global variable demangling so I am
pre-emptively disabling it until we can get the demangling support added.

Importantly, uniquefying global variables is not needed right now as we do not
do profile attribution to global vars based on sampling. It was added for
completeness and so this feature is not exactly missed.

Differential Revision: https://reviews.llvm.org/D98392
2021-03-11 20:59:30 -08:00
Mircea Trofin 11b70b9e3a Revert "[NPM][CGSCC] FunctionAnalysisManagerCGSCCProxy: do not clear immutable function passes"
This reverts commit 5eaeb0fa67.

It appears there are analyses that assume clearing - example:
https://lab.llvm.org/buildbot#builders/36/builds/5964
2021-03-11 18:31:19 -08:00
Mircea Trofin 5eaeb0fa67 [NPM][CGSCC] FunctionAnalysisManagerCGSCCProxy: do not clear immutable function passes
Check with the analysis result by calling invalidate instead of clear on
the analysis manager.

Differential Revision: https://reviews.llvm.org/D98440
2021-03-11 18:15:28 -08:00
Florian Hahn c92ec0dd92
[Matrix] Add support for matrix-by-scalar division.
This patch extends the matrix spec to allow matrix-by-scalar division.

Originally support for `/` was left out to avoid ambiguity for the
matrix-matrix version of `/`, which could either be elementwise or
specified as matrix multiplication M1 * (1/M2).

For the matrix-scalar version, no ambiguity exists; `*` is also
an elementwise operation in that case. Matrix-by-scalar division
is commonly supported by systems including Matlab, Mathematica
or NumPy.

Reviewed By: rjmccall

Differential Revision: https://reviews.llvm.org/D97857
2021-03-11 22:21:23 +00:00
Petr Hosek 87fd09b25f [InstrProfiling] Generate runtime hook for ELF platforms
When using -fprofile-list to selectively apply instrumentation only
to certain files or functions, we may end up with a binary that doesn't
have any counters in the case where no files were selected. However,
because on Linux and Fuchsia, we pass -u__llvm_profile_runtime, the
runtime would still be pulled in and incur some non-trivial overhead,
especially in the case when the continuous or runtime counter relocation
mode is being used. A better way would be to pull in the profile runtime
only when needed by declaring the __llvm_profile_runtime symbol in the
translation unit only when needed.

This approach was already used prior to 9a041a7522, but we changed it
to always generate the __llvm_profile_runtime due to a TAPI limitation.
Since TAPI is only used on Mach-O platforms, we could use the early
emission of __llvm_profile_runtime there, and on other platforms we
could change back to the earlier approach where the symbol is generated
later only when needed. We can stop passing -u__llvm_profile_runtime to
the linker on Linux and Fuchsia since the generated undefined symbol in
each translation unit that needed it serves the same purpose.

Differential Revision: https://reviews.llvm.org/D98061
2021-03-11 12:29:01 -08:00
Joseph Huber 807466ef28 [OpenMP] Restore backwards compatibility for libomptarget
Summary:
The changes introduced in D87946 changed the API for libomptarget
functions. `__kmpc_push_target_tripcount` was a function in Clang 11.x
but was not given a backward-compatible interface. This change will
require people using Clang 13.x or 12.x to recompile their offloading
programs.

Reviewed By: jdoerfert cchen

Differential Revision: https://reviews.llvm.org/D98358
2021-03-11 09:52:11 -05:00
Nathan James cb559c8d5e
[Sema] Add some basic lambda capture fix-its
Adds fix-its when users forget to explicitly capture variables or this in lambdas

Addresses https://github.com/clangd/clangd/issues/697

Reviewed By: kbobyrev

Differential Revision: https://reviews.llvm.org/D96975
2021-03-11 13:46:25 +00:00
Olivier Goffart 5baea05601 [SEH] Fix capture of this in lambda functions
Commit 1b04bdc2f3 added support for
capturing the 'this' pointer in a SEH context (__finally or __except),
But the case in which the 'this' pointer is part of a lambda capture
was not handled properly

Differential Revision: https://reviews.llvm.org/D97687
2021-03-11 09:12:42 +01:00
Zakk Chen d6a0560bf2 [Clang][RISCV] Add custom TableGen backend for riscv-vector intrinsics.
Demonstrate how to generate vadd/vfadd intrinsic functions

1. add -gen-riscv-vector-builtins for clang builtins.
2. add -gen-riscv-vector-builtin-codegen for clang codegen.
3. add -gen-riscv-vector-header for riscv_vector.h. It also generates
ifdef directives with extension checking, base on D94403.
4. add -gen-riscv-vector-generic-header for riscv_vector_generic.h.
Generate overloading version Header for generic api.
https://github.com/riscv/rvv-intrinsic-doc/blob/master/rvv-intrinsic-rfc.md#c11-generic-interface
5. update tblgen doc for riscv related options.

riscv_vector.td also defines some unused type transformers for vadd,
because I think it could demonstrate how tranfer type work and we need
them for the whole intrinsic functions implementation in the future.

Authored-by: Roger Ferrer Ibanez <rofirrim@gmail.com>
Co-Authored-by: Zakk Chen <zakk.chen@sifive.com>

Reviewed By: jrtc27, craig.topper, HsiangKai, Jim, Paul-C-Anagnostopoulos

Differential Revision: https://reviews.llvm.org/D95016
2021-03-10 18:43:43 -08:00
Leonard Chan 70af0bf6fe [clang][Driver] Expose -fexperimental-relative-c++-abi-vtables flag
Initially, this flag was meant to only be used through cc1 and not directly
through the clang driver. However, we accidentally ended up using this flag
as a driver flag already for selecting multilibs within the fuchsia toolchain.
We're currently in an awkward state where it's only accepted as a driver flag
when targeting Fuchsia, and all other instances it can only be added via
-Xclang. Since we're ready to use this in Fuchsia, we can just expose this to
the driver for simplicity.

Differential Revision: https://reviews.llvm.org/D98375
2021-03-10 16:28:40 -08:00
Giorgis Georgakoudis ecf68972fd Revert "Replace func name with regex in update_cc_test_checks"
This reverts commit bf58d6a1f9.

Breaks tests, fix
2021-03-10 15:05:35 -08:00
zoecarver a89ac0dd18 Update __is_unsigned builtin to match the Standard.
Updates __is_unsigned to have the same behavior as the standard
specifies. This is in line with 511dbd8, which applied the same change
to __is_signed.

Refs D67897.

Differential Revision: https://reviews.llvm.org/D98104
2021-03-10 15:00:26 -08:00
Giorgis Georgakoudis bf58d6a1f9 Replace func name with regex in update_cc_test_checks
The patch adds an argument to update_cc_test_checks for replacing a function name matching a regex. This functionality is needed to match generated function signatures that include file hashes. Example:

The function signature for the following function:

`__omp_offloading_50_b84c41e__Z9ftemplateIiET_i_l30_worker`

with `--replace-function-regex "__omp_offloading_[0-9]+_[a-z0-9]+_(.*)"` will become:

`CHECK-LABEL: @{{__omp_offloading_[0-9]+_[a-z0-9]+__Z9ftemplateIiET_i_l30_worker}}(`

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D97107
2021-03-10 12:57:35 -08:00
Giorgis Georgakoudis a2abe2259c Run non-filechecked commands in update_cc_test_checks.py
Some tests in clang require running non-filechecked commands to generate the actual filecheck input. For example, tests for openmp offloading require generating the host bc without any checking, before running the clang command to actually generate the filechecked IR of the target device. This patch enables `update_cc_test_checks.py` to run non-filechecked run lines in-place.

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D97068
2021-03-10 12:25:35 -08:00
Arthur Eubanks c8227f06b3 [clang] Don't assert in EmitAggregateCopy on trivial_abi types
Fixes PR42961.

Reviewed By: rnk

Differential Revision: https://reviews.llvm.org/D97872
2021-03-10 10:16:06 -08:00
Jingu Kang 25951c5ab8 [AArch64] Add missing intrinsics for scalar FP rounding
Differential Revision: https://reviews.llvm.org/D98269
2021-03-10 13:22:29 +00:00
Balazs Benics a94ac467c2 [analyzer][CTU][NFC] Fix "Add an extra regression test"
As thakis reported, I will replace `rm -r` by `rm -rf`.
I hope it fixes the build bot.
2021-03-10 13:07:49 +01:00
Adam Balogh bcc662484a [analyzer] Crash fix for alpha.cplusplus.IteratorRange
If the non-iterator side of an iterator operation
`+`, `+=`, `-` or `-=` is `UndefinedVal` an assertions happens.
This small fix prevents this.

Patch by Adam Balogh.

Reviewed By: NoQ

Differential Revision: https://reviews.llvm.org/D85424
2021-03-10 12:42:24 +01:00