[PATCH] D17212: [ThinLTO] Support for call graph in per-module and combined summary.

[Teresa Johnson via llvm-commits]

tejohnson updated this revision to Diff 50287.
tejohnson added a comment.

Fixes to findRefEdges discussed in review and IRC

Two main changes to findRefEdges:

1. Use worklist iteration instead of recursion

The reason is that when we invoke with an Instruction, it will iterate
into other instructions in the function when it encounters a use of
a local variable defined in another instruction. Ultimately we are
analyzing all instructions in the function, and we prevent duplicate
work by sharing the Visited set across all instructions in the function.
However, using a worklist approach is more efficient for large functions
where with recursion we may end up recursing many times (using much
stack).

2. More accurate detection and skipping of callsite references

The prior solution would miss the non-call reference to foo in the
following case:
foo((void *)foo);
since we were skipping all GVs that matched the callee GV.

Additionally, as noted in 1) we may traverse through local variables
defined on other instructions. Those other instructions may be calls
which return a value. We want to make sure we don't count calls in other
instructions encountered this way as non-call refs. Depending on the
order of traversal (e.g. a use on a phi encountered before the call
instruction), we can't count on the call being in the visited set.

Finally, doing the checking for callsites here avoids the need for
WriteFunction to special case call instructions, which has its own set
of issues. For example, one solution considered was for call
instructions to invoke findRefEdges on each of its data_ops(). This
means findRefEdges would need to distinguish between a GV user that was
passed in being either a reference (if it was a call instruction
operand) or a global variable for which we want to analyze initializers
(i.e.  called from WriteModuleLevelReferences).

Finally, enhanced the new test quite a bit to check for the various
cases I encountered when fixing findRefEdges.


http://reviews.llvm.org/D17212

Files:
  include/llvm/Bitcode/LLVMBitCodes.h
  include/llvm/Bitcode/ReaderWriter.h
  include/llvm/IR/FunctionInfo.h
  include/llvm/Object/FunctionIndexObjectFile.h
  include/llvm/ProfileData/ProfileCommon.h
  lib/Bitcode/Reader/BitcodeReader.cpp
  lib/Bitcode/Writer/BitcodeWriter.cpp
  lib/Bitcode/Writer/LLVMBuild.txt
  lib/IR/FunctionInfo.cpp
  lib/Object/FunctionIndexObjectFile.cpp
  lib/Transforms/IPO/FunctionImport.cpp
  test/Bitcode/Inputs/thinlto-function-summary-callgraph-pgo.ll
  test/Bitcode/Inputs/thinlto-function-summary-callgraph.ll
  test/Bitcode/thinlto-function-summary-callgraph-pgo.ll
  test/Bitcode/thinlto-function-summary-callgraph.ll
  test/Bitcode/thinlto-function-summary-refgraph.ll
  test/Bitcode/thinlto-function-summary.ll
  test/Bitcode/thinlto-summary-linkage-types.ll
  test/tools/gold/X86/thinlto.ll
  test/tools/llvm-lto/thinlto.ll
  tools/gold/gold-plugin.cpp
  tools/llvm-bcanalyzer/llvm-bcanalyzer.cpp
  tools/llvm-lto/llvm-lto.cpp

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