dda73336ad
The motivating use case is to support import the function declaration across modules to construct call graph edges for indirect calls [1] when importing the function definition costs too much compile time (e.g., the function is too large has no `noinline` attribute). 1. Currently, when the compiled IR module doesn't have a function definition but its postlink combined summary contains the function summary or a global alias summary with this function as aliasee, the function definition will be imported from source module by IRMover. The implementation is in FunctionImporter::importFunctions [2] 2. In order for FunctionImporter to import a declaration of a function, both function summary and alias summary need to carry the def / decl state. Specifically, all existing summary fields doesn't differ across import modules, but the def / decl state of is decided by `<ImportModule, Function>`. This change encodes the def/decl state in `GlobalValueSummary::GVFlags`. In the subsequent changes 1. The indexing step `computeImportForModule` [3] will compute the set of definitions and the set of declarations for each module, and passing on the information to bitcode writer. 2. Bitcode writer will look up the def/decl state and sets the state when it writes out the flag value. This is demonstrated in https://github.com/llvm/llvm-project/pull/87600 3. Function importer will read the def/decl state when reading the combined summary to figure out two sets of global values, and IRMover will be updated to import the declaration (aka linkGlobalValuePrototype [4]) into the destination module. - The next change is https://github.com/llvm/llvm-project/pull/87600 [1] mentioned in rfc https://discourse.llvm.org/t/rfc-for-better-call-graph-sort-build-a-more-complete-call-graph-by-adding-more-indirect-call-edges/74029#support-cross-module-function-declaration-import-5 [2]3b337242ee/llvm/lib/Transforms/IPO/FunctionImport.cpp (L1608-L1764)[3]3b337242ee/llvm/lib/Transforms/IPO/FunctionImport.cpp (L856)[4]3b337242ee/llvm/lib/Linker/IRMover.cpp (L605)
47 lines
885 B
YAML
47 lines
885 B
YAML
---
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GlobalValueMap:
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42:
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- Live: true
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ImportType: 0
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TypeTestAssumeVCalls:
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- GUID: 123
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Offset: 0
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- GUID: 456
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Offset: 4
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TypeCheckedLoadVCalls:
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- GUID: 789
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Offset: 8
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- GUID: 1234
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Offset: 16
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TypeTestAssumeConstVCalls:
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- VFunc:
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GUID: 123
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Offset: 4
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Args: [12, 24]
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TypeCheckedLoadConstVCalls:
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- VFunc:
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GUID: 456
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Offset: 8
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Args: [24, 12]
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43:
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- Live: true
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ImportType : 1
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TypeIdMap:
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typeid1:
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WPDRes:
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0:
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Kind: Indir
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4:
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Kind: Indir
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ResByArg:
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"":
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Kind: UniformRetVal
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Info: 12
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12:
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Kind: UniformRetVal
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Info: 24
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"12,24":
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Kind: UniformRetVal
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Info: 48
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...
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