forked from OSchip/llvm-project
83d03ddbf6
Summary: The patch to move metadata linking after global value linking didn't correctly map unmaterialized global values to null as desired. They were in fact mapped to the source copy. It largely worked by accident since most module linker clients destroyed the source module which caused the source GVs to be replaced by null, but caused a failure with LTO linking on Windows: http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20151109/312869.html The problem is that a null return value from materializeValueFor is handled by mapping the value to self. This is the desired behavior when materializeValueFor is passed a non-GlobalValue. The problem is how to distinguish that case from the case where we really do want to map to null. This patch addresses this by passing in a new flag to the value mapper indicating that unmapped global values should be mapped to null. Other Value types are handled as before. Note that the documented behavior of asserting on unmapped values when the flag RF_IgnoreMissingValues isn't set is currently disabled with FIXME notes due to bootstrap failures. I modified these disabled asserts so when they are eventually enabled again it won't assert for the unmapped values when the new RF_NullMapMissingGlobalValues flag is set. I also considered using a callback into the value materializer, but a flag seemed cleaner given that there are already existing flags. I also considered modifying materializeValueFor to return the input value when we want to map to source and then treat a null return to mean map to null. However, there are other value materializer subclasses that implement materializeValueFor, and they would all need to be audited and the return values possibly changed, which seemed error-prone. Reviewers: dexonsmith, joker.eph Subscribers: pcc, llvm-commits Differential Revision: http://reviews.llvm.org/D14682 llvm-svn: 253170 |
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| LinkModules.cpp | ||
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