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author | Mingming Liu <mingmingl@google.com> | 2024-04-10 19:46:01 -0700 |
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committer | GitHub <noreply@github.com> | 2024-04-10 19:46:01 -0700 |
commit | dda73336ad22bd0b5ecda17040c50fb10fcbe5fb (patch) | |
tree | c5655d75797516814f2508c98dc21408e7e67e8f /llvm/lib/Bitcode | |
parent | 999b9e6ddb4324600a46c8f7006acec81fe3af0f (diff) | |
download | llvm-dda73336ad22bd0b5ecda17040c50fb10fcbe5fb.zip llvm-dda73336ad22bd0b5ecda17040c50fb10fcbe5fb.tar.gz llvm-dda73336ad22bd0b5ecda17040c50fb10fcbe5fb.tar.bz2 |
[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
`<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] 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
Diffstat (limited to 'llvm/lib/Bitcode')
-rw-r--r-- | llvm/lib/Bitcode/Reader/BitcodeReader.cpp | 3 | ||||
-rw-r--r-- | llvm/lib/Bitcode/Writer/BitcodeWriter.cpp | 2 |
2 files changed, 4 insertions, 1 deletions
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 diff --git a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp index dd554e4..6d01e3b 100644 --- a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp +++ b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp @@ -1217,6 +1217,8 @@ static uint64_t getEncodedGVSummaryFlags(GlobalValueSummary::GVFlags Flags) { RawFlags |= (Flags.Visibility << 8); // 2 bits + RawFlags |= (Flags.ImportType << 10); // 1 bit + return RawFlags; } |