Metadata (via ValueAsMetadata) can reference constant expressions
that may no longer be supported. These references can both be in
function-local metadata and module metadata, if the same expression
is used in multiple functions. At least in theory, such references
could also be in metadata proper, rather than just inside
ValueAsMetadata references in calls.

Instead of trying to expand these expressions (which we can't
reliably do), pretend that the constant has been deleted, which
means that ValueAsMetadata references will get replaced with
undef metadata.

Fixes https://github.com/llvm/llvm-project/issues/68281.

This fixes the bitcode upgrade failure reported in
https://reviews.llvm.org/D155924#4616789.

The expansion always happens in the entry block, so this may be
inaccurate if there are trapping constant expressions.

When opaque pointers are enabled and old IR with typed pointers is read,
the BitcodeReader automatically upgrades all typed pointers to opaque
pointers. This is a lossy conversion, i.e. when a function argument is a
pointer and unused, it’s impossible to reconstruct the original type
behind the pointer.

There are cases where the type information of pointers is needed. One is
reading DXIL, which is bitcode of old LLVM IR and makes a lot of use of
pointers in function signatures.
We’d like to keep using up-to-date llvm to read in and process DXIL, so
in the face of opaque pointers, we need some way to access the type
information of pointers from the read bitcode.

This patch allows extracting type information by supplying functions to
parseBitcodeFile that get called for each function signature or metadata
value. The function can access the type information via the reader’s
type IDs and the getTypeByID and getContainedTypeID functions.
The tests exemplarily shows how type info from pointers can be stored in
metadata for use after the BitcodeReader finished.

Differential Revision: https://reviews.llvm.org/D127728

This reverts commit b56df190b01335506ce30a4559d880da76d1a181.

The unit tests are implemented in a way that requires support for
writing typed pointer bitcode, which is going away soon. Please
rewrite it in a way that not have requirement, e.g. by shipping
pre-compiled bitcode, as we do for integration tests.

When opaque pointers are enabled and old IR with typed pointers is read,
the BitcodeReader automatically upgrades all typed pointers to opaque
pointers. This is a lossy conversion, i.e. when a function argument is a
pointer and unused, it’s impossible to reconstruct the original type
behind the pointer.

There are cases where the type information of pointers is needed. One is
reading DXIL, which is bitcode of old LLVM IR and makes a lot of use of
pointers in function signatures.
We’d like to keep using up-to-date llvm to read in and process DXIL, so
in the face of opaque pointers, we need some way to access the type
information of pointers from the read bitcode.

This patch allows extracting type information by supplying functions to
parseBitcodeFile that get called for each function signature or metadata
value. The function can access the type information via the reader’s
type IDs and the getTypeByID and getContainedTypeID functions.
The tests exemplarily shows how type info from pointers can be stored in
metadata for use after the BitcodeReader finished.

Differential Revision: https://reviews.llvm.org/D127728

Major user-facing changes:
llvm/Bitcode/BitcodeReader.h no longer includes llvm/IR/ModuleSummaryIndex.h

Some statistics:
clang++ -E  -Iinclude -I../llvm/include ../llvm/lib/Bitcode/Reader/*.cpp -std=c++14 -fno-rtti -fno-exceptions | wc -l
after: 493335
before: 539640

Discourse thread on the topic: https://discourse.llvm.org/t/include-what-you-use-include-cleanup/

Differential Revision: https://reviews.llvm.org/D119091

We need to include Error.h already

to reflect the new license.

We understand that people may be surprised that we're moving the header
entirely to discuss the new license. We checked this carefully with the
Foundation's lawyer and we believe this is the correct approach.

Essentially, all code in the project is now made available by the LLVM
project under our new license, so you will see that the license headers
include that license only. Some of our contributors have contributed
code under our old license, and accordingly, we have retained a copy of
our old license notice in the top-level files in each project and
repository.

llvm-svn: 351636

Summary:
Followup from D53596/r346891. Remove the getMDNodeFwdRefOrNull interface
to the MDLoader since it is no longer used. Also improve error messages
when the internal implementation is used within the MDLoader.

Reviewers: steven_wu

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D54542

llvm-svn: 346899