caio/clang-p2996
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[BOLT] Never emit "large" functions (#115974)

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"Large" functions are functions that are too big to fit into their
original slots after code modifications. CheckLargeFunctions pass is
designed to prevent such functions from emission. Extend this pass to
work with functions with constant islands.

Now that CheckLargeFunctions covers all functions, it guarantees that we
will never see such functions after code emission on all platforms
(previously it was guaranteed on x86 only). Hence, we can get rid of
RewriteInstance extensions that were meant to support "large" functions.
This commit is contained in:
Maksim Panchenko
2024-11-13 09:58:44 -08:00
committed by GitHub
parent 6b2de10c68
commit 1b8e0cf090
5 changed files with 28 additions and 55 deletions
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31
bolt/lib/Rewrite/RewriteInstance.cpp
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@@ -3807,7 +3807,6 @@ void RewriteInstance::mapCodeSections(BOLTLinker::SectionMapper MapSection) {
if (!Function.isEmitted())
continue;
bool TooLarge = false;
ErrorOr<BinarySection &> FuncSection = Function.getCodeSection();
assert(FuncSection && "cannot find section for function");
FuncSection->setOutputAddress(Function.getAddress());
@@ -3818,11 +3817,8 @@ void RewriteInstance::mapCodeSections(BOLTLinker::SectionMapper MapSection) {
MapSection(*FuncSection, Function.getAddress());
Function.setImageAddress(FuncSection->getAllocAddress());
Function.setImageSize(FuncSection->getOutputSize());
if (Function.getImageSize() > Function.getMaxSize()) {
assert(!BC->isX86() && "Unexpected large function.");
TooLarge = true;
FailedAddresses.emplace_back(Function.getAddress());
}
assert(Function.getImageSize() <= Function.getMaxSize() &&
"Unexpected large function");
// Map jump tables if updating in-place.
if (opts::JumpTables == JTS_BASIC) {
@@ -3852,19 +3848,11 @@ void RewriteInstance::mapCodeSections(BOLTLinker::SectionMapper MapSection) {
assert(ColdSection && "cannot find section for cold part");
// Cold fragments are aligned at 16 bytes.
NextAvailableAddress = alignTo(NextAvailableAddress, 16);
if (TooLarge) {
// The corresponding FDE will refer to address 0.
FF.setAddress(0);
FF.setImageAddress(0);
FF.setImageSize(0);
FF.setFileOffset(0);
} else {
FF.setAddress(NextAvailableAddress);
FF.setImageAddress(ColdSection->getAllocAddress());
FF.setImageSize(ColdSection->getOutputSize());
FF.setFileOffset(getFileOffsetForAddress(NextAvailableAddress));
ColdSection->setOutputAddress(FF.getAddress());
}
FF.setAddress(NextAvailableAddress);
FF.setImageAddress(ColdSection->getAllocAddress());
FF.setImageSize(ColdSection->getOutputSize());
FF.setFileOffset(getFileOffsetForAddress(NextAvailableAddress));
ColdSection->setOutputAddress(FF.getAddress());
LLVM_DEBUG(
dbgs() << formatv(
@@ -3872,9 +3860,6 @@ void RewriteInstance::mapCodeSections(BOLTLinker::SectionMapper MapSection) {
FF.getImageAddress(), FF.getAddress(), FF.getImageSize()));
MapSection(*ColdSection, FF.getAddress());
if (TooLarge)
BC->deregisterSection(*ColdSection);
NextAvailableAddress += FF.getImageSize();
}
@@ -5814,7 +5799,7 @@ void RewriteInstance::writeEHFrameHeader() {
getFileOffsetForAddress(NextAvailableAddress);
std::vector<char> NewEHFrameHdr = CFIRdWrt->generateEHFrameHeader(
RelocatedEHFrame, NewEHFrame, EHFrameHdrOutputAddress, FailedAddresses);
RelocatedEHFrame, NewEHFrame, EHFrameHdrOutputAddress);
Out->os().seek(EHFrameHdrFileOffset);
Out->os().write(NewEHFrameHdr.data(), NewEHFrameHdr.size());