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Merging r229421:

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r229421 | dexonsmith | 2015-02-16 11:18:01 -0800 (Mon, 16 Feb 2015) | 33 lines

Bitcode: Fix major regression: large files w/ debug info

The metadata/value split introduced a major regression reading large
bitcode files that contain debug info (or other cyclic (non-self
reference) metadata graphs).  For the first time in a while, I dropped
from libLTO.dylib down to `llvm-lto` with a non-trivial bitcode file
(~350MB), and I hit this when reading the result of ld64's `-save-temps`
in `llvm-lto`.

Here's pseudo-code for what was going on:

    read-main-metadata-block:
      for each md:
        if has-fwd-ref: // Only true for cyclic graphs.
          any-fwd-refs <- true
      if any-fwd-refs:
        foreach md:
          resolve-cycles(md) // Handle cycles.

    foreach function:
      read-function-metadata-block: // Such as !alias, !loop
        if any-fwd-refs:
          foreach md: // (all metadata, not just this block)
            resolve-cycles(md) // A no-op, but the loop is expensive!!

This commit resets the `AnyFwdRefs` flag to `false`.  This on its own
was enough to change my Release+Asserts `llvm-lto` time for reading this
bitcode from over 20 minutes (I gave up on it) to 20 seconds.  I've gone
further by tracking the min/max metadata forward-references in a
metadata block.  This protects against a schema that has lots of
functions that each reference their own metadata cycle.

Unfortunately, this regression is in the 3.6 branch as well.
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_36@229545 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Hans Wennborg
2015-02-17 21:27:11 +00:00
parent 35b927f016
commit 310571dfd1
2 changed files with 17 additions and 3 deletions
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18
lib/Bitcode/Reader/BitcodeReader.cpp
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@@ -538,9 +538,17 @@ Metadata *BitcodeReaderMDValueList::getValueFwdRef(unsigned Idx) {
if (Metadata *MD = MDValuePtrs[Idx])
return MD;
// Create and return a placeholder, which will later be RAUW'd.
AnyFwdRefs = true;
// Track forward refs to be resolved later.
if (AnyFwdRefs) {
MinFwdRef = std::min(MinFwdRef, Idx);
MaxFwdRef = std::max(MaxFwdRef, Idx);
} else {
AnyFwdRefs = true;
MinFwdRef = MaxFwdRef = Idx;
}
++NumFwdRefs;
// Create and return a placeholder, which will later be RAUW'd.
Metadata *MD = MDNode::getTemporary(Context, None);
MDValuePtrs[Idx].reset(MD);
return MD;
@@ -556,11 +564,15 @@ void BitcodeReaderMDValueList::tryToResolveCycles() {
return;
// Resolve any cycles.
for (auto &MD : MDValuePtrs) {
for (unsigned I = MinFwdRef, E = MaxFwdRef + 1; I != E; ++I) {
auto &MD = MDValuePtrs[I];
assert(!(MD && isa<MDNodeFwdDecl>(MD)) && "Unexpected forward reference");
if (auto *N = dyn_cast_or_null<UniquableMDNode>(MD))
N->resolveCycles();
}
// Make sure we return early again until there's another forward ref.
AnyFwdRefs = false;
}
Type *BitcodeReader::getTypeByID(unsigned ID) {