[Driver] -###: exit with code 1 if hasErrorOccurred

The exit code for -### is inconsistent. Unrecognized options lead to
exit code 1, as expected. However, most others errors (including invalid
opti

[Driver] -###: exit with code 1 if hasErrorOccurred

The exit code for -### is inconsistent. Unrecognized options lead to
exit code 1, as expected. However, most others errors (including invalid
option value) lead to exit code 0, differing from GCC and most utilities.

This is a longstanding quirk of -###, and we didn't fix it because many
driver tests need adjustment.

Change -### to be similar to -fdriver-only -v and exit with code 1.

This requires fixing many driver tests, but the end result gives us
stronger tests.

* Existing `RUN: %clang -### ...` tests usually don't use `CHECK-NOT: error:` or `--implicit-check-not=error:`.
If a change introduces an error, such a change usually cannot be detected.
* Many folks contributing new tests don't know `-fdriver-only -v`.
To test no driver error/warning for new tests, they can use the familiar `-### -Werror`
instead of `-fdriver-only -v -Werror`.

An incomplete list of prerequisite test improvement:

* 2f79bb10461d114783a1548201928549ace09755: add -nogpulib to some AMDGPU tests
* 9155e517e6e1cda474d0d0fa82f71696c325bc10: add --cuda-path= (test w/ and w/o /usr/local/cuda)
* 80765ede5bbcca1364c2d4ae06127011eaba6389: -mcpu=native may return either 0 or 1, depending on whether `--target=` specifies a native target
* abae53f43f0d1da8d8e421f4a628d7ec64d6e365: fix -fuse-ld=lld misuses (test w/o and w/o /usr/local/bin/ld.lld)
* ab68df505e5bb8808ee44f53044b50ca7575098e: add -resource-dir= and -fvisibility=hidden
to some -fsanitize=cfi tests
* d5ca1602f64114f612ad5630f04e4aa90591c78d: --rtlib=platform without --unwindlib= may fail if CLANG_DEFAULT_UNWINDLIB=unwindlib

Reviewed By: jhuber6, yaxunl, dblaikie

Differential Revision: https://reviews.llvm.org/D156363

show more ...

Revert D156363 "[Driver] -###: exit with code 1 if hasErrorOccurred"

This reverts commit 8c3550b1a78fde7bf28f420da8447d9fde37017f.

clang/test/Driver/fsanitize.c has a mysterious failure worth
inves

Revert D156363 "[Driver] -###: exit with code 1 if hasErrorOccurred"

This reverts commit 8c3550b1a78fde7bf28f420da8447d9fde37017f.

clang/test/Driver/fsanitize.c has a mysterious failure worth
investigation.

show more ...

[Driver] -###: exit with code 1 if hasErrorOccurred

The exit code for -### is inconsistent. Unrecognized options lead to
exit code 1, as expected. However, most others errors (including invalid
opti

[Driver] -###: exit with code 1 if hasErrorOccurred

The exit code for -### is inconsistent. Unrecognized options lead to
exit code 1, as expected. However, most others errors (including invalid
option value) lead to exit code 0, differing from GCC and most utilities.

This is a longstanding quirk of -###, and we didn't fix it because many
driver tests need adjustment.

Change -### to be similar to -fdriver-only -v and exit with code 1.

This requires fixing many driver tests, but the end result gives us
stronger tests.

* Existing `RUN: %clang -### ...` tests usually don't use `CHECK-NOT: error:` or `--implicit-check-not=error:`.
If a change introduces an error, such a change usually cannot be detected.
* Many folks contributing new tests don't know `-fdriver-only -v`.
To test no driver error/warning for new tests, they can use the familiar `-### -Werror`
instead of `-fdriver-only -v -Werror`.

An incomplete list of prerequisite test improvement:

* 2f79bb10461d114783a1548201928549ace09755: add -nogpulib to some AMDGPU tests
* 9155e517e6e1cda474d0d0fa82f71696c325bc10: add --cuda-path= (test w/ and w/o /usr/local/cuda)
* 80765ede5bbcca1364c2d4ae06127011eaba6389: -mcpu=native may return either 0 or 1, depending on whether `--target=` specifies a native target
* abae53f43f0d1da8d8e421f4a628d7ec64d6e365: fix -fuse-ld=lld misuses (test w/o and w/o /usr/local/bin/ld.lld)

Reviewed By: jhuber6, yaxunl, dblaikie

Differential Revision: https://reviews.llvm.org/D156363

show more ...

Revert D156363 "[Driver] -###: exit with code 1 if hasErrorOccurred"

This reverts commit e39bf32b3bc2f0cc21d783ba789bd82553493875.

Some tests have different behaviors depent on whether certain dire

Revert D156363 "[Driver] -###: exit with code 1 if hasErrorOccurred"

This reverts commit e39bf32b3bc2f0cc21d783ba789bd82553493875.

Some tests have different behaviors depent on whether certain directories/files are present on the host.
An incomplete list from https://lab.llvm.org/buildbot/#/builders/109/builds/70149

csky-toolchain.c
riscv*-toolchain.c
fuchsia.*
hip-*
ohos.c

show more ...

[Driver] -###: exit with code 1 if hasErrorOccurred

The exit code for -### is inconsistent. Unrecognized options lead to
exit code 1, as expected. However, most others errors (including invalid
opti

[Driver] -###: exit with code 1 if hasErrorOccurred

The exit code for -### is inconsistent. Unrecognized options lead to
exit code 1, as expected. However, most others errors (including invalid
option value) lead to exit code 0, differing from GCC and most utilities.

This is a longstanding quirk of -###, and we didn't fix it because many
driver tests need adjustment.

Change -### to be similar to -fdriver-only -v and exit with code 1.

This requires fixing many driver tests, but the end result gives us
stronger tests.

* Existing `RUN: %clang -### ...` tests usually don't use `CHECK-NOT: error:` or `--implicit-check-not=error:`.
If a change introduces an error, such a change usually cannot be detected.
* Many folks contributing new tests don't know `-fdriver-only -v`.
To test no driver error/warning for new tests, they can use the familiar `-### -Werror`
instead of `-fdriver-only -v -Werror`.

Reviewed By: jhuber6, yaxunl, dblaikie

Differential Revision: https://reviews.llvm.org/D156363

show more ...

Reland: Dead Virtual Function Elimination

Remove dead virtual functions from vtables with
replaceNonMetadataUsesWith, so that CGProfile metadata gets cleaned up
correctly.

Original commit message:

Reland: Dead Virtual Function Elimination

Remove dead virtual functions from vtables with
replaceNonMetadataUsesWith, so that CGProfile metadata gets cleaned up
correctly.

Original commit message:

Currently, it is hard for the compiler to remove unused C++ virtual
functions, because they are all referenced from vtables, which are referenced
by constructors. This means that if the constructor is called from any live
code, then we keep every virtual function in the final link, even if there
are no call sites which can use it.

This patch allows unused virtual functions to be removed during LTO (and
regular compilation in limited circumstances) by using type metadata to match
virtual function call sites to the vtable slots they might load from. This
information can then be used in the global dead code elimination pass instead
of the references from vtables to virtual functions, to more accurately
determine which functions are reachable.

To make this transformation safe, I have changed clang's code-generation to
always load virtual function pointers using the llvm.type.checked.load
intrinsic, instead of regular load instructions. I originally tried writing
this using clang's existing code-generation, which uses the llvm.type.test
and llvm.assume intrinsics after doing a normal load. However, it is possible
for optimisations to obscure the relationship between the GEP, load and
llvm.type.test, causing GlobalDCE to fail to find virtual function call
sites.

The existing linkage and visibility types don't accurately describe the scope
in which a virtual call could be made which uses a given vtable. This is
wider than the visibility of the type itself, because a virtual function call
could be made using a more-visible base class. I've added a new
!vcall_visibility metadata type to represent this, described in
TypeMetadata.rst. The internalization pass and libLTO have been updated to
change this metadata when linking is performed.

This doesn't currently work with ThinLTO, because it needs to see every call
to llvm.type.checked.load in the linkage unit. It might be possible to
extend this optimisation to be able to use the ThinLTO summary, as was done
for devirtualization, but until then that combination is rejected in the
clang driver.

To test this, I've written a fuzzer which generates random C++ programs with
complex class inheritance graphs, and virtual functions called through object
and function pointers of different types. The programs are spread across
multiple translation units and DSOs to test the different visibility
restrictions.

I've also tried doing bootstrap builds of LLVM to test this. This isn't
ideal, because only classes in anonymous namespaces can be optimised with
-fvisibility=default, and some parts of LLVM (plugins and bugpoint) do not
work correctly with -fvisibility=hidden. However, there are only 12 test
failures when building with -fvisibility=hidden (and an unmodified compiler),
and this change does not cause any new failures for either value of
-fvisibility.

On the 7 C++ sub-benchmarks of SPEC2006, this gives a geomean code-size
reduction of ~6%, over a baseline compiled with "-O2 -flto
-fvisibility=hidden -fwhole-program-vtables". The best cases are reductions
of ~14% in 450.soplex and 483.xalancbmk, and there are no code size
increases.

I've also run this on a set of 8 mbed-os examples compiled for Armv7M, which
show a geomean size reduction of ~3%, again with no size increases.

I had hoped that this would have no effect on performance, which would allow
it to awlays be enabled (when using -fwhole-program-vtables). However, the
changes in clang to use the llvm.type.checked.load intrinsic are causing ~1%
performance regression in the C++ parts of SPEC2006. It should be possible to
recover some of this perf loss by teaching optimisations about the
llvm.type.checked.load intrinsic, which would make it worth turning this on
by default (though it's still dependent on -fwhole-program-vtables).

Differential revision: https://reviews.llvm.org/D63932

llvm-svn: 375094

show more ...

Dead Virtual Function Elimination

Currently, it is hard for the compiler to remove unused C++ virtual
functions, because they are all referenced from vtables, which are referenced
by constructors. T

Dead Virtual Function Elimination

Currently, it is hard for the compiler to remove unused C++ virtual
functions, because they are all referenced from vtables, which are referenced
by constructors. This means that if the constructor is called from any live
code, then we keep every virtual function in the final link, even if there
are no call sites which can use it.

This patch allows unused virtual functions to be removed during LTO (and
regular compilation in limited circumstances) by using type metadata to match
virtual function call sites to the vtable slots they might load from. This
information can then be used in the global dead code elimination pass instead
of the references from vtables to virtual functions, to more accurately
determine which functions are reachable.

To make this transformation safe, I have changed clang's code-generation to
always load virtual function pointers using the llvm.type.checked.load
intrinsic, instead of regular load instructions. I originally tried writing
this using clang's existing code-generation, which uses the llvm.type.test
and llvm.assume intrinsics after doing a normal load. However, it is possible
for optimisations to obscure the relationship between the GEP, load and
llvm.type.test, causing GlobalDCE to fail to find virtual function call
sites.

The existing linkage and visibility types don't accurately describe the scope
in which a virtual call could be made which uses a given vtable. This is
wider than the visibility of the type itself, because a virtual function call
could be made using a more-visible base class. I've added a new
!vcall_visibility metadata type to represent this, described in
TypeMetadata.rst. The internalization pass and libLTO have been updated to
change this metadata when linking is performed.

This doesn't currently work with ThinLTO, because it needs to see every call
to llvm.type.checked.load in the linkage unit. It might be possible to
extend this optimisation to be able to use the ThinLTO summary, as was done
for devirtualization, but until then that combination is rejected in the
clang driver.

To test this, I've written a fuzzer which generates random C++ programs with
complex class inheritance graphs, and virtual functions called through object
and function pointers of different types. The programs are spread across
multiple translation units and DSOs to test the different visibility
restrictions.

I've also tried doing bootstrap builds of LLVM to test this. This isn't
ideal, because only classes in anonymous namespaces can be optimised with
-fvisibility=default, and some parts of LLVM (plugins and bugpoint) do not
work correctly with -fvisibility=hidden. However, there are only 12 test
failures when building with -fvisibility=hidden (and an unmodified compiler),
and this change does not cause any new failures for either value of
-fvisibility.

On the 7 C++ sub-benchmarks of SPEC2006, this gives a geomean code-size
reduction of ~6%, over a baseline compiled with "-O2 -flto
-fvisibility=hidden -fwhole-program-vtables". The best cases are reductions
of ~14% in 450.soplex and 483.xalancbmk, and there are no code size
increases.

I've also run this on a set of 8 mbed-os examples compiled for Armv7M, which
show a geomean size reduction of ~3%, again with no size increases.

I had hoped that this would have no effect on performance, which would allow
it to awlays be enabled (when using -fwhole-program-vtables). However, the
changes in clang to use the llvm.type.checked.load intrinsic are causing ~1%
performance regression in the C++ parts of SPEC2006. It should be possible to
recover some of this perf loss by teaching optimisations about the
llvm.type.checked.load intrinsic, which would make it worth turning this on
by default (though it's still dependent on -fwhole-program-vtables).

Differential revision: https://reviews.llvm.org/D63932

llvm-svn: 374539

show more ...