[ThinLTO] Update combined index for SamplePGO indirect calls to locals

In ThinLTO for locals we normally compute the GUID from the name after
prepending the source path to get a unique global id. SamplePGO indirect
call profiles contain the target GUID without this uniquification,
however (unless compiling with -funique-internal-linkage-names).

In order to correctly handle the call edges added to the combined index
for these indirect calls, during importing and bitcode writing we
consult a map of original to full GUID to identify the actual callee.
However, for a large application this was consuming a lot of compile
time as we need to do this repeatedly (especially during importing where
we may traverse call edges multiple times).

To fix this implement a suggestion in one of the FIXME comments, and
actually modify the call edges during a single traversal after the index
is built to perform the fixups once. I combined this fixup with the dead
code analysis performed on the index in order to avoid adding an
additional walk of the index. The dead code analysis is the first
analysis performed on the index.

This reduced the time required for a large thin link with SamplePGO by
about 20%.

No new test added, but I confirmed that there are existing tests that
will fail when no fixup is performed.

Differential Revision: https://reviews.llvm.org/D110374

1 files changed, 1 insertions, 27 deletions

diff --git a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
index 402840e..9ddc4a2 100644
--- a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
+++ b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
@@ -4208,33 +4208,7 @@ void IndexBitcodeWriter::writeCombinedGlobalValueSummary() {
     }
 
     auto GetValueId = [&](const ValueInfo &VI) -> Optional<unsigned> {
-      GlobalValue::GUID GUID = VI.getGUID();
-      Optional<unsigned> CallValueId = getValueId(GUID);
-      if (CallValueId)
-        return CallValueId;
-      // For SamplePGO, the indirect call targets for local functions will
-      // have its original name annotated in profile. We try to find the
-      // corresponding PGOFuncName as the GUID.
-      GUID = Index.getGUIDFromOriginalID(GUID);
-      if (!GUID)
-        return None;
-      CallValueId = getValueId(GUID);
-      if (!CallValueId)
-        return None;
-      // The mapping from OriginalId to GUID may return a GUID
-      // that corresponds to a static variable. Filter it out here.
-      // This can happen when
-      // 1) There is a call to a library function which does not have
-      // a CallValidId;
-      // 2) There is a static variable with the  OriginalGUID identical
-      // to the GUID of the library function in 1);
-      // When this happens, the logic for SamplePGO kicks in and
-      // the static variable in 2) will be found, which needs to be
-      // filtered out.
-      auto *GVSum = Index.getGlobalValueSummary(GUID, false);
-      if (GVSum && GVSum->getSummaryKind() == GlobalValueSummary::GlobalVarKind)
-        return None;
-      return CallValueId;
+      return getValueId(VI.getGUID());
     };
 
     auto *FS = cast<FunctionSummary>(S);