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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)
30 lines
1.5 KiB
LLVM
30 lines
1.5 KiB
LLVM
; Tests that `llvm-dis` could disassemble ThinLTO minimized bitcode
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; (e.g., bitcode generated by `opt --thin-link-bitcode-file=<minimized-bitcode>`,
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; or `clang -Xclang -fthin-link-bitcode=<minimized-bitcode>`)
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; %t.o is the thin-lto ready bitcode, and %t.thinlink.bc is the minimized bitcode.
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; RUN: opt -thinlto-bc %s -thin-link-bitcode-file=%t.thinlink.bc -o %t.o
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; With default options, `llvm-dis` returns invalid record for ThinLTO minimized bitcode.
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; RUN: not llvm-dis %t.thinlink.bc 2>&1 | FileCheck %s --check-prefix=INVALID-RECORD
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; INVALID-RECORD: Invalid record
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; Tests that `llvm-dis` could disassemble minimized bitcode with `--print-thinlto-index-only`, and verify its content.
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; RUN: llvm-dis --print-thinlto-index-only %t.thinlink.bc -o - | FileCheck %s --check-prefix=DIS
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; Tests that `llvm-dis` could disassemble ThinLTO-ready bitcode with `--print-thinlto-index-only`,
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; and verify its content.
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; RUN: llvm-dis --print-thinlto-index-only %t.o -o - | FileCheck %s --check-prefix=DIS
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; DIS: ^0 = module: (path: "{{.*}}thinlto-index-disassembled-by-llvm-dis.ll.tmp
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; DIS: ^1 = gv: (name: "aplusb", summaries: (function: (module: ^0, flags: (linkage: external, visibility: default, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0, importType: definition), insts: 2))) ; guid =
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source_filename = "add.cpp"
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target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
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target triple = "x86_64-unknown-linux-gnu"
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define i32 @aplusb(i32 %a, i32 %b) {
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%add = add i32 %b, %a
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ret i32 %add
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}
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