Reapply "AsmPrinter: Change DIEValue to be stored by value"

This reverts commit r238350, effectively reapplying r238349 after fixing
(all?) the problems, all somehow related to how I was using
`AlignedArrayCharUnion<>` inside `DIEValue`:

  - MSVC can only handle `sizeof()` on types, not values.  Change the
    assert.
  - GCC doesn't know the `is_trivially_copyable` type trait.  Instead of
    asserting it, add destructors.
  - Call placement new even when constructing POD (i.e., the pointers).
  - Instead of copying the char buffer, copy the casted classes.

I've left in a couple of `static_assert`s that I think both MSVC and GCC
know how to handle.  If the bots disagree with me, I'll remove them.

  - Check that the constructed type is either standard layout or a
    pointer.  This protects against a programming error: we really want
    the "small" `DIEValue`s to be small and simple, so don't
    accidentally change them not to be.
  - Similarly, check that the size of the buffer is no bigger than a
    `uint64_t` or a pointer.  (I thought checking against
    `sizeof(uint64_t)` would be good enough, but Chandler suggested that
    pointers might sometimes be bigger than that in the context of
    sanitizers.)

I've also committed r238359 in the meantime, which introduces a
DIEValue.def to simplify dispatching between the various types (thanks
to a review comment by David Blaikie).  Without that, this commit would
be almost unintelligible.

Here's the original commit message:
--
Change `DIEValue` to be stored/passed/etc. by value, instead of
reference.  It's now a discriminated union, with a `Val` field storing
the actual type.  The classes that used to inherit from `DIEValue` no
longer do.  There are two categories of these:

  - Small values fit in a single pointer and are stored by value.
  - Large values require auxiliary storage, and are stored by reference.

The only non-mechanical change is to tools/dsymutil/DwarfLinker.cpp.  It
was relying on `DIEInteger`s being passed around by reference, so I
replaced that assumption with a `PatchLocation` type that stores a safe
reference to where the `DIEInteger` lives instead.

This commit causes a temporary regression in memory usage, since I've
left merging `DIEAbbrevData` into `DIEValue` for a follow-up commit.  I
measured an increase from 845 MB to 879 MB, around 3.9%.  The follow-up
drops it lower than the starting point, and I've only recently brought
the memory this low anyway, so I'm committing these changes separately
to keep them incremental.  (I also considered swapping the commits, but
the other one first would cause a lot more code churn.)

(I'm looking at `llc` memory usage on `verify-uselistorder.lto.opt.bc`;
see r236629 for details.)
--

llvm-svn: 238362

1 files changed, 10 insertions, 15 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
index c10e70352af..2256200c8d0 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
@@ -42,8 +42,7 @@ void DwarfCompileUnit::addLabelAddress(DIE &Die, dwarf::Attribute Attribute,
     DD->addArangeLabel(SymbolCU(this, Label));
 
   unsigned idx = DD->getAddressPool().getIndex(Label);
-  DIEValue *Value = new (DIEValueAllocator) DIEInteger(idx);
-  Die.addValue(Attribute, dwarf::DW_FORM_GNU_addr_index, Value);
+  Die.addValue(Attribute, dwarf::DW_FORM_GNU_addr_index, DIEInteger(idx));
 }
 
 void DwarfCompileUnit::addLocalLabelAddress(DIE &Die,
@@ -53,8 +52,7 @@ void DwarfCompileUnit::addLocalLabelAddress(DIE &Die,
     DD->addArangeLabel(SymbolCU(this, Label));
 
   Die.addValue(Attribute, dwarf::DW_FORM_addr,
-               Label ? (DIEValue *)new (DIEValueAllocator) DIELabel(Label)
-                     : new (DIEValueAllocator) DIEInteger(0));
+               Label ? DIEValue(DIELabel(Label)) : DIEValue(DIEInteger(0)));
 }
 
 unsigned DwarfCompileUnit::getOrCreateSourceID(StringRef FileName,
@@ -145,7 +143,7 @@ DIE *DwarfCompileUnit::getOrCreateGlobalVariableDIE(
   bool addToAccelTable = false;
   if (auto *Global = dyn_cast_or_null<GlobalVariable>(GV->getVariable())) {
     addToAccelTable = true;
-    DIELoc *Loc = new (DIEValueAllocator) DIELoc();
+    DIELoc *Loc = new (DIEValueAllocator) DIELoc;
     const MCSymbol *Sym = Asm->getSymbol(Global);
     if (Global->isThreadLocal()) {
       // FIXME: Make this work with -gsplit-dwarf.
@@ -183,7 +181,7 @@ DIE *DwarfCompileUnit::getOrCreateGlobalVariableDIE(
   } else if (const ConstantExpr *CE = getMergedGlobalExpr(GV->getVariable())) {
     addToAccelTable = true;
     // GV is a merged global.
-    DIELoc *Loc = new (DIEValueAllocator) DIELoc();
+    DIELoc *Loc = new (DIEValueAllocator) DIELoc;
     Value *Ptr = CE->getOperand(0);
     MCSymbol *Sym = Asm->getSymbol(cast<GlobalValue>(Ptr));
     DD->addArangeLabel(SymbolCU(this, Sym));
@@ -365,10 +363,9 @@ void DwarfCompileUnit::constructScopeDIE(
 
 void DwarfCompileUnit::addSectionDelta(DIE &Die, dwarf::Attribute Attribute,
                                        const MCSymbol *Hi, const MCSymbol *Lo) {
-  DIEValue *Value = new (DIEValueAllocator) DIEDelta(Hi, Lo);
   Die.addValue(Attribute, DD->getDwarfVersion() >= 4 ? dwarf::DW_FORM_sec_offset
                                                      : dwarf::DW_FORM_data4,
-               Value);
+               new (DIEValueAllocator) DIEDelta(Hi, Lo));
 }
 
 void DwarfCompileUnit::addScopeRangeList(DIE &ScopeDIE,
@@ -515,7 +512,7 @@ DwarfCompileUnit::constructVariableDIEImpl(const DbgVariable &DV,
     return VariableDie;
 
   auto Expr = DV.getExpression().begin();
-  DIELoc *Loc = new (DIEValueAllocator) DIELoc();
+  DIELoc *Loc = new (DIEValueAllocator) DIELoc;
   DIEDwarfExpression DwarfExpr(*Asm, *this, *Loc);
   for (auto FI : DV.getFrameIndex()) {
     unsigned FrameReg = 0;
@@ -739,7 +736,7 @@ void DwarfCompileUnit::addVariableAddress(const DbgVariable &DV, DIE &Die,
 /// Add an address attribute to a die based on the location provided.
 void DwarfCompileUnit::addAddress(DIE &Die, dwarf::Attribute Attribute,
                                   const MachineLocation &Location) {
-  DIELoc *Loc = new (DIEValueAllocator) DIELoc();
+  DIELoc *Loc = new (DIEValueAllocator) DIELoc;
 
   bool validReg;
   if (Location.isReg())
@@ -761,7 +758,7 @@ void DwarfCompileUnit::addAddress(DIE &Die, dwarf::Attribute Attribute,
 void DwarfCompileUnit::addComplexAddress(const DbgVariable &DV, DIE &Die,
                                          dwarf::Attribute Attribute,
                                          const MachineLocation &Location) {
-  DIELoc *Loc = new (DIEValueAllocator) DIELoc();
+  DIELoc *Loc = new (DIEValueAllocator) DIELoc;
   DIEDwarfExpression DwarfExpr(*Asm, *this, *Loc);
   assert(DV.getExpression().size() == 1);
   const DIExpression *Expr = DV.getExpression().back();
@@ -782,10 +779,9 @@ void DwarfCompileUnit::addComplexAddress(const DbgVariable &DV, DIE &Die,
 /// Add a Dwarf loclistptr attribute data and value.
 void DwarfCompileUnit::addLocationList(DIE &Die, dwarf::Attribute Attribute,
                                        unsigned Index) {
-  DIEValue *Value = new (DIEValueAllocator) DIELocList(Index);
   dwarf::Form Form = DD->getDwarfVersion() >= 4 ? dwarf::DW_FORM_sec_offset
                                                 : dwarf::DW_FORM_data4;
-  Die.addValue(Attribute, Form, Value);
+  Die.addValue(Attribute, Form, DIELocList(Index));
 }
 
 void DwarfCompileUnit::applyVariableAttributes(const DbgVariable &Var,
@@ -802,8 +798,7 @@ void DwarfCompileUnit::applyVariableAttributes(const DbgVariable &Var,
 /// Add a Dwarf expression attribute data and value.
 void DwarfCompileUnit::addExpr(DIELoc &Die, dwarf::Form Form,
                                const MCExpr *Expr) {
-  DIEValue *Value = new (DIEValueAllocator) DIEExpr(Expr);
-  Die.addValue((dwarf::Attribute)0, Form, Value);
+  Die.addValue((dwarf::Attribute)0, Form, DIEExpr(Expr));
 }
 
 void DwarfCompileUnit::applySubprogramAttributesToDefinition(