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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)
13 lines
1.3 KiB
LLVM
13 lines
1.3 KiB
LLVM
; Checks that llvm-as/llvm-dis correctly assembles/disassembles index with
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; multiple summaries with single GUID.
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; RUN: llvm-as %s -o - | llvm-dis -o - | FileCheck %s
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source_filename = "index.bc"
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^0 = module: (path: "[Regular LTO]", hash: (0, 0, 0, 0, 0))
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; CHECK: ^0 = module: (path: "[Regular LTO]", hash: (0, 0, 0, 0, 0))
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^1 = module: (path: "main.bc", hash: (3499594384, 1671013073, 3271036935, 1830411232, 59290952))
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; CHECK-NEXT: ^1 = module: (path: "main.bc", hash: (3499594384, 1671013073, 3271036935, 1830411232, 59290952))
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^2 = gv: (guid: 13351721993301222997, summaries: (function: (module: ^1, flags: (linkage: linkonce_odr, visibility: default, notEligibleToImport: 0, live: 1, dsoLocal: 1, canAutoHide: 0, importType: definition), insts: 1), function: (module: ^1, flags: (linkage: available_externally, notEligibleToImport: 1, live: 1, dsoLocal: 1, canAutoHide: 0, importType: definition), insts: 1)))
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; CHECK-NEXT: ^2 = gv: (guid: 13351721993301222997, summaries: (function: (module: ^1, flags: (linkage: linkonce_odr, visibility: default, notEligibleToImport: 0, live: 1, dsoLocal: 1, canAutoHide: 0, importType: definition), insts: 1), function: (module: ^1, flags: (linkage: available_externally, visibility: default, notEligibleToImport: 1, live: 1, dsoLocal: 1, canAutoHide: 0, importType: definition), insts: 1)))
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