Duncan P. N. Exon Smith 387a89bb36 Reapply "Linker: Drop function pointers for overridden subprograms" ... This reverts commit r233254, effectively reapplying r233164 (and its successors), with an additional testcase for when subprograms match exactly. This fixes PR22792 (again). I'm using the same approach, but I've moved up the call to `stripReplacedSubprograms()`. The function pointers need to be dropped before mapping any metadata from the source module, or else this can drop the function from new subprograms that have merged (via Metadata uniquing) with the old ones. Dropping the pointers first prevents them from merging. **** The original commit message follows. **** Linker: Drop function pointers for overridden subprograms Instead of dropping subprograms that have been overridden, just set their function pointers to `nullptr`. This is a minor adjustment to the stop-gap fix for PR21910 committed in r224487, and fixes the crasher from PR22792. The problem that r224487 put a band-aid on: how do we find the canonical subprogram for a `Function`? Since the backend currently relies on `DebugInfoFinder` (which does a naive in-order traversal of compile units and picks the first subprogram) for this, r224487 tried dropping non-canonical subprograms. Dropping subprograms fails because the backend *also* builds up a map from subprogram to compile unit (`DwarfDebug::SPMap`) based on the subprogram lists. A missing subprogram causes segfaults later when an inlined reference (such as in this testcase) is created. Instead, just drop the `Function` pointer to `nullptr`, which nicely mirrors what happens when an already-inlined `Function` is optimized out. We can't really be sure that it's the same definition anyway, as the testcase demonstrates. This still isn't completely satisfactory. Two flaws at least that I can think of: - I still haven't found a straightforward way to make this symmetric in the IR. (Interestingly, the DWARF output is already symmetric, and I've tested for that to be sure we don't regress.) - Using `DebugInfoFinder` to find the canonical subprogram for a function is kind of crazy. We should just attach metadata to the function, like this: define weak i32 @foo(i32, i32) !dbg !MDSubprogram(...) { git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@233302 91177308-0d34-0410-b5e6-96231b3b80d8		2015-03-26 18:35:30 +00:00
..
CMakeLists.txt	Use ADDITIONAL_HEADER_DIRS in all LLVM CMake projects.	2015-02-11 03:28:02 +00:00
LinkModules.cpp	Reapply "Linker: Drop function pointers for overridden subprograms"	2015-03-26 18:35:30 +00:00
LLVMBuild.txt	[Linker] Kill Linker::LoadObject which is dead, and drop the BitReader dependency again.	2013-01-18 19:37:11 +00:00
Makefile