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[NFC] Make getPreferredAlignment honor section markings. 

This should more accurately reflect what the AsmPrinter will actually
do.

This is NFC, as far as I can tell; all the places that might be affected
already have an extra check to avoid using the result of
getPreferredAlignment in this situation.

Differential Revision: https://reviews.llvm.org/D51377

llvm-svn: 340999
This commit is contained in:
Eli Friedman 2018-08-29 23:46:26 +00:00
parent 6556e6b929
commit 3769639335
2 changed files with 16 additions and 11 deletions
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11
llvm/lib/CodeGen/GlobalMerge.cpp
View File

@ -462,17 +462,8 @@ bool GlobalMerge::doMerge(const SmallVectorImpl<GlobalVariable *> &Globals,
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.
// Make sure we use the same alignment AsmPrinter would use.
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);

16
llvm/lib/IR/DataLayout.cpp
View File

@ -808,15 +808,29 @@ int64_t DataLayout::getIndexedOffsetInType(Type *ElemTy,
/// global. This includes an explicitly requested alignment (if the global
/// has one).
unsigned DataLayout::getPreferredAlignment(const GlobalVariable *GV) const {
unsigned GVAlignment = GV->getAlignment();
// If a section is specified, always precisely honor explicit alignment,
// so we don't insert padding into a section we don't control.
if (GVAlignment && GV->hasSection())
return GVAlignment;
// If no explicit alignment is specified, compute the alignment based on
// the IR type. If an alignment is specified, increase it to match the ABI
// alignment of the IR type.
//
// FIXME: Not sure it makes sense to use the alignment of the type if
// there's already an explicit alignment specification.
Type *ElemType = GV->getValueType();
unsigned Alignment = getPrefTypeAlignment(ElemType);
unsigned GVAlignment = GV->getAlignment();
if (GVAlignment >= Alignment) {
Alignment = GVAlignment;
} else if (GVAlignment != 0) {
Alignment = std::max(GVAlignment, getABITypeAlignment(ElemType));
}
// If no explicit alignment is specified, and the global is large, increase
// the alignment to 16.
// FIXME: Why 16, specifically?
if (GV->hasInitializer() && GVAlignment == 0) {
if (Alignment < 16) {
// If the global is not external, see if it is large. If so, give it a