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)
44 lines
1.9 KiB
LLVM
44 lines
1.9 KiB
LLVM
; REQUIRES: x86-registered-target
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; Test that FunctionAttr Propagation is generating correct summaries
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; RUN: split-file %s %t
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; RUN: opt -module-summary %t/a.ll -o %t/a.bc
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; RUN: opt -module-summary %t/b.ll -o %t/b.bc
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; RUN: llvm-lto2 run -disable-thinlto-funcattrs=0 %t/a.bc %t/b.bc -o %t1.o -save-temps \
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; RUN: -r=%t/a.bc,call_extern,plx \
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; RUN: -r=%t/a.bc,extern, \
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; RUN: -r=%t/b.bc,extern,p
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; RUN: llvm-dis %t1.o.index.bc -o - | FileCheck %s --check-prefix=CHECK-INDEX
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; RUN: llvm-dis %t1.o.1.1.promote.bc -o - | FileCheck %s --check-prefix=CHECK-IR
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;; Summary for call_extern. Note that llvm-lto2 writes out the index before propagation occurs so call_extern doesn't have its flags updated.
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; CHECK-INDEX: ^2 = gv: (guid: 13959900437860518209, summaries: (function: (module: ^0, flags: (linkage: external, visibility: default, notEligibleToImport: 0, live: 1, dsoLocal: 1, canAutoHide: 0, importType: definition), insts: 2, calls: ((callee: ^3)))))
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;; Summary for extern
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; CHECK-INDEX: ^3 = gv: (guid: 14959766916849974397, summaries: (function: (module: ^1, flags: (linkage: external, visibility: default, notEligibleToImport: 0, live: 1, dsoLocal: 0, canAutoHide: 0, importType: definition), insts: 1, funcFlags: (readNone: 0, readOnly: 0, noRecurse: 1, returnDoesNotAlias: 0, noInline: 0, alwaysInline: 0, noUnwind: 1, mayThrow: 0, hasUnknownCall: 0, mustBeUnreachable: 0))))
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;--- a.ll
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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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declare void @extern()
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; CHECK-IR: Function Attrs: norecurse nounwind
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; CHECK-IR-NEXT: define dso_local void @call_extern()
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define void @call_extern() {
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call void @extern()
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ret void
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}
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;--- b.ll
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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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attributes #0 = { nounwind norecurse }
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define void @extern() #0 {
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ret void
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}
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