From dda73336ad22bd0b5ecda17040c50fb10fcbe5fb Mon Sep 17 00:00:00 2001 From: Mingming Liu Date: Wed, 10 Apr 2024 19:46:01 -0700 Subject: [ThinLTO]Record import type in GlobalValueSummary::GVFlags (#87597) 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 ``. 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] https://github.com/llvm/llvm-project/blob/3b337242ee165554f0017b00671381ec5b1ba855/llvm/lib/Transforms/IPO/FunctionImport.cpp#L1608-L1764 [3] https://github.com/llvm/llvm-project/blob/3b337242ee165554f0017b00671381ec5b1ba855/llvm/lib/Transforms/IPO/FunctionImport.cpp#L856 [4] https://github.com/llvm/llvm-project/blob/3b337242ee165554f0017b00671381ec5b1ba855/llvm/lib/Linker/IRMover.cpp#L605 --- llvm/lib/Bitcode/Reader/BitcodeReader.cpp | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'llvm/lib/Bitcode/Reader/BitcodeReader.cpp') diff --git a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp index 92c3495..fe4f0d6 100644 --- a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp +++ b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp @@ -1141,6 +1141,7 @@ static GlobalValueSummary::GVFlags getDecodedGVSummaryFlags(uint64_t RawFlags, // to getDecodedLinkage() will need to be taken into account here as above. auto Linkage = GlobalValue::LinkageTypes(RawFlags & 0xF); // 4 bits auto Visibility = GlobalValue::VisibilityTypes((RawFlags >> 8) & 3); // 2 bits + auto IK = GlobalValueSummary::ImportKind((RawFlags >> 10) & 1); // 1 bit RawFlags = RawFlags >> 4; bool NotEligibleToImport = (RawFlags & 0x1) || Version < 3; // The Live flag wasn't introduced until version 3. For dead stripping @@ -1151,7 +1152,7 @@ static GlobalValueSummary::GVFlags getDecodedGVSummaryFlags(uint64_t RawFlags, bool AutoHide = (RawFlags & 0x8); return GlobalValueSummary::GVFlags(Linkage, Visibility, NotEligibleToImport, - Live, Local, AutoHide); + Live, Local, AutoHide, IK); } // Decode the flags for GlobalVariable in the summary -- cgit v1.1