[GlobalMerge] Allow merging globals with explicit section markings.
At least on ELF, it's impossible to tell from the object file whether
two globals with the same section marking were merged: the merged global
uses "private" linkage to hide its symbol, and the aliases look like
regular symbols. I can't think of any other reason to disallow it.
(Of course, we can only merge globals in the same section.)
The weird alignment handling matches AsmPrinter; our alignment handling
for global variables should probably be refactored.
Differential Revision: https://reviews.llvm.org/D49822
llvm-svn: 338791
diff --git a/llvm/lib/CodeGen/GlobalMerge.cpp b/llvm/lib/CodeGen/GlobalMerge.cpp
index 9f7f5e3..f4526c6 100644
--- a/llvm/lib/CodeGen/GlobalMerge.cpp
+++ b/llvm/lib/CodeGen/GlobalMerge.cpp
@@ -461,7 +461,18 @@
unsigned CurIdx = 0;
for (j = i; j != -1; j = GlobalSet.find_next(j)) {
Type *Ty = Globals[j]->getValueType();
+
+ // Make sure we use the same alignment AsmPrinter would use. There
+ // currently isn't any helper to compute that, so we compute it
+ // explicitly here.
+ //
+ // getPreferredAlignment will sometimes return an alignment higher
+ // than the explicitly specified alignment; we must ignore that
+ // if the section is explicitly specified, to avoid inserting extra
+ // padding into that section.
unsigned Align = DL.getPreferredAlignment(Globals[j]);
+ if (Globals[j]->hasSection() && Globals[j]->getAlignment())
+ Align = Globals[j]->getAlignment();
unsigned Padding = alignTo(MergedSize, Align) - MergedSize;
MergedSize += Padding;
MergedSize += DL.getTypeAllocSize(Ty);
@@ -516,6 +527,7 @@
GlobalVariable::NotThreadLocal, AddrSpace);
MergedGV->setAlignment(MaxAlign);
+ MergedGV->setSection(Globals[i]->getSection());
const StructLayout *MergedLayout = DL.getStructLayout(MergedTy);
for (ssize_t k = i, idx = 0; k != j; k = GlobalSet.find_next(k), ++idx) {
@@ -599,16 +611,15 @@
IsMachO = Triple(M.getTargetTriple()).isOSBinFormatMachO();
auto &DL = M.getDataLayout();
- DenseMap<unsigned, SmallVector<GlobalVariable *, 16>> Globals, ConstGlobals,
- BSSGlobals;
+ DenseMap<std::pair<unsigned, StringRef>, SmallVector<GlobalVariable *, 16>>
+ Globals, ConstGlobals, BSSGlobals;
bool Changed = false;
setMustKeepGlobalVariables(M);
// Grab all non-const globals.
for (auto &GV : M.globals()) {
// Merge is safe for "normal" internal or external globals only
- if (GV.isDeclaration() || GV.isThreadLocal() ||
- GV.hasSection() || GV.hasImplicitSection())
+ if (GV.isDeclaration() || GV.isThreadLocal() || GV.hasImplicitSection())
continue;
// It's not safe to merge globals that may be preempted
@@ -623,6 +634,7 @@
assert(PT && "Global variable is not a pointer!");
unsigned AddressSpace = PT->getAddressSpace();
+ StringRef Section = GV.getSection();
// Ignore all 'special' globals.
if (GV.getName().startswith("llvm.") ||
@@ -637,26 +649,26 @@
if (DL.getTypeAllocSize(Ty) < MaxOffset) {
if (TM &&
TargetLoweringObjectFile::getKindForGlobal(&GV, *TM).isBSSLocal())
- BSSGlobals[AddressSpace].push_back(&GV);
+ BSSGlobals[{AddressSpace, Section}].push_back(&GV);
else if (GV.isConstant())
- ConstGlobals[AddressSpace].push_back(&GV);
+ ConstGlobals[{AddressSpace, Section}].push_back(&GV);
else
- Globals[AddressSpace].push_back(&GV);
+ Globals[{AddressSpace, Section}].push_back(&GV);
}
}
for (auto &P : Globals)
if (P.second.size() > 1)
- Changed |= doMerge(P.second, M, false, P.first);
+ Changed |= doMerge(P.second, M, false, P.first.first);
for (auto &P : BSSGlobals)
if (P.second.size() > 1)
- Changed |= doMerge(P.second, M, false, P.first);
+ Changed |= doMerge(P.second, M, false, P.first.first);
if (EnableGlobalMergeOnConst)
for (auto &P : ConstGlobals)
if (P.second.size() > 1)
- Changed |= doMerge(P.second, M, true, P.first);
+ Changed |= doMerge(P.second, M, true, P.first.first);
return Changed;
}