Add an index for Module Metadata record in the bitcode

This index record the position for each metadata record in
the bitcode, so that the reader will be able to lazy-load
on demand each individual

Add an index for Module Metadata record in the bitcode

This index record the position for each metadata record in
the bitcode, so that the reader will be able to lazy-load
on demand each individual record.

We also make sure that every abbrev is emitted upfront so
that the block can be skipped while reading.

I don't plan to commit this before having the reader
counterpart, but I figured this can be reviewed mostly
independently.

Recommit r290684 (was reverted in r290686 because a test
was broken) after adding a threshold to avoid emitting
the index when unnecessary (little amount of metadata).
This optimization "hides" a limitation of the ability
to backpatch in the bitstream: we can only backpatch
safely when the position has been flushed. So if we emit
an index for one metadata, it is possible that (part of)
the offset placeholder hasn't been flushed and the backpatch
will fail.

Differential Revision: https://reviews.llvm.org/D28083

llvm-svn: 290690

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Revert "Add an index for Module Metadata record in the bitcode"

This reverts commit a0ca6ae2d38339e4ede0dfa588086fc23d87e836. Revert at
Mehdi's request as it is breaking bots.

llvm-svn: 290686

Add an index for Module Metadata record in the bitcode

Summary:
This index record the position for each metadata record in
the bitcode, so that the reader will be able to lazy-load
on demand each in

Add an index for Module Metadata record in the bitcode

Summary:
This index record the position for each metadata record in
the bitcode, so that the reader will be able to lazy-load
on demand each individual record.

We also make sure that every abbrev is emitted upfront so
that the block can be skipped while reading.

I don't plan to commit this before having the reader
counterpart, but I figured this can be reviewed mostly
independently.

Reviewers: pcc, tejohnson

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D28083

llvm-svn: 290684

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BitcodeWriter: Emit metadata in post-order (again)

Emit metadata nodes in post-order. The iterative algorithm from r266709
failed to maintain this property. After understanding my mistake, it
wasn

BitcodeWriter: Emit metadata in post-order (again)

Emit metadata nodes in post-order. The iterative algorithm from r266709
failed to maintain this property. After understanding my mistake, it
wasn't too hard to write a test with llvm-bcanalyzer (and I've actually
made this change once before: see r220340).

This also reverts the "noisy" testcase change from r266709. That should
have been more of a red flag :/.

Note: The same bug crept into the ValueMapper in r265456. I'm still
working on the fix.

llvm-svn: 266947

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BitcodeWriter: Break recursion when enumerating Metadata, almost NFC

Use a worklist instead of recursing through MDNode operands in
ValueEnumerator. The actual record output order has changed sligh

BitcodeWriter: Break recursion when enumerating Metadata, almost NFC

Use a worklist instead of recursing through MDNode operands in
ValueEnumerator. The actual record output order has changed slightly,
but otherwise there's no functionality change.

I had to update test/Bitcode/metadata-function-blocks.ll. I renumbered
nodes so they continue to match the implicit record ids.

llvm-svn: 266709

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Bitcode: Try to emit metadata in function blocks

Whenever metadata is only referenced by a single function, emit the
metadata just in that function block. This should improve lazy-loading
by reduci

Bitcode: Try to emit metadata in function blocks

Whenever metadata is only referenced by a single function, emit the
metadata just in that function block. This should improve lazy-loading
by reducing the amount of metadata in the global block.

For now, this should catch all DILocations, and anything else that
happens to be referenced only by a single function.

It's also a first step toward a couple of possible future directions
(which this commit does *not* implement):

1. Some debug info metadata is only referenced from compile units and
individual functions. If we can drop the link from the compile
unit, this optimization will get more powerful.

2. Any uniqued metadata that isn't referenced globally can in theory be
emitted in every function block that references it (trading off
bitcode size and full-parse time vs. lazy-load time).

Note: this assumes the new BitcodeReader error checking from r265223.
The metadata stored in function blocks gets purged after parsing each
function, which means unresolved forward references will get lost.
Since all the global metadata should have already been resolved by the
time we get to the function metadata blocks we just need to check for
that case. (If for some reason we need to handle bitcode that fails the
checks in r265223, the fix is to store about-to-be-dropped unresolved
nodes in MetadataList::shrinkTo until they can be handled succesfully by
a future call to MetadataList::tryToResolveCycles.)

llvm-svn: 265226

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