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)
27 lines
1.2 KiB
LLVM
27 lines
1.2 KiB
LLVM
; RUN: opt -module-summary %s -o %t1.bc
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; RUN: opt -module-summary %p/Inputs/funcimport_alwaysinline.ll -o %t2.bc
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; RUN: llvm-lto2 run -disable-thinlto-funcattrs=0 %t1.bc %t2.bc -o %t.o -save-temps \
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; RUN: -r=%t1.bc,foo,plx \
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; RUN: -r=%t2.bc,main,plx \
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; RUN: -r=%t2.bc,foo,l \
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; RUN: -import-instr-limit=0
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; RUN: llvm-dis %t.o.2.3.import.bc -o - | FileCheck %s --check-prefix=CHECK1
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; RUN: llvm-dis %t.o.index.bc -o - | FileCheck %s --check-prefix=CHECK2
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; foo() being always_inline should be imported irrespective of the
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; instruction limit
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; CHECK1: define available_externally void @foo()
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target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
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target triple = "x86_64-unknown-linux-gnu"
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; Function Attrs: alwaysinline nounwind uwtable
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define void @foo() #0 {
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entry:
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ret void
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}
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attributes #0 = { alwaysinline nounwind uwtable }
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; CHECK2: ^2 = gv: (guid: {{.*}}, summaries: (function: (module: ^0, flags: (linkage: external, visibility: default, notEligibleToImport: 0, live: 1, dsoLocal: 1, canAutoHide: 0, importType: definition), insts: 1, funcFlags: (readNone: 0, readOnly: 0, noRecurse: 0, returnDoesNotAlias: 0, noInline: 0, alwaysInline: 1, noUnwind: 1, mayThrow: 0, hasUnknownCall: 0, mustBeUnreachable: 0))))
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