[GlobalISel] Add a type to MachineInstr.

We actually need that information only for generic instructions, therefore it
would be nice not to have to pay the extra memory consumption for all
instructions. Especially because a typed non-generic instruction does not make
sense.

The question is then, is it possible to have that information in a union or
something?
My initial thought was that we could have a derived class GenericMachineInstr
with additional information, but in practice it makes little to no sense since
generic MachineInstrs are likely turned into non-generic ones by just switching
the opcode. In other words, we don't want to go through the process of creating
a new, non-generic MachineInstr, object each time we do this switch. The memory
benefit probably is not worth the extra compile time.

Another option would be to keep the type of the MachineInstr in a side table.
This would induce an extra indirection though.

Anyway, I will file a PR to discuss about it and remember we need to come back
to it at some point.

llvm-svn: 260558

1 files changed, 20 insertions, 5 deletions

diff --git a/llvm/lib/CodeGen/MachineInstr.cpp b/llvm/lib/CodeGen/MachineInstr.cpp
index 37573f5928e..805acb93efd 100644
--- a/llvm/lib/CodeGen/MachineInstr.cpp
+++ b/llvm/lib/CodeGen/MachineInstr.cpp
@@ -653,7 +653,12 @@ MachineInstr::MachineInstr(MachineFunction &MF, const MCInstrDesc &tid,
                            DebugLoc dl, bool NoImp)
     : MCID(&tid), Parent(nullptr), Operands(nullptr), NumOperands(0), Flags(0),
       AsmPrinterFlags(0), NumMemRefs(0), MemRefs(nullptr),
-      debugLoc(std::move(dl)) {
+      debugLoc(std::move(dl))
+#ifdef LLVM_BUILD_GLOBAL_ISEL
+      ,
+      Ty(nullptr)
+#endif
+{
   assert(debugLoc.hasTrivialDestructor() && "Expected trivial destructor");
 
   // Reserve space for the expected number of operands.
@@ -670,10 +675,14 @@ MachineInstr::MachineInstr(MachineFunction &MF, const MCInstrDesc &tid,
 /// MachineInstr ctor - Copies MachineInstr arg exactly
 ///
 MachineInstr::MachineInstr(MachineFunction &MF, const MachineInstr &MI)
-  : MCID(&MI.getDesc()), Parent(nullptr), Operands(nullptr), NumOperands(0),
-    Flags(0), AsmPrinterFlags(0),
-    NumMemRefs(MI.NumMemRefs), MemRefs(MI.MemRefs),
-    debugLoc(MI.getDebugLoc()) {
+    : MCID(&MI.getDesc()), Parent(nullptr), Operands(nullptr), NumOperands(0),
+      Flags(0), AsmPrinterFlags(0), NumMemRefs(MI.NumMemRefs),
+      MemRefs(MI.MemRefs), debugLoc(MI.getDebugLoc())
+#ifdef LLVM_BUILD_GLOBAL_ISEL
+      ,
+      Ty(nullptr)
+#endif
+{
   assert(debugLoc.hasTrivialDestructor() && "Expected trivial destructor");
 
   CapOperands = OperandCapacity::get(MI.getNumOperands());
@@ -1677,6 +1686,12 @@ void MachineInstr::print(raw_ostream &OS, ModuleSlotTracker &MST,
   else
     OS << "UNKNOWN";
 
+
+#ifdef LLVM_BUILD_GLOBAL_ISEL
+  if (Ty)
+    OS << ' ' << *Ty << ' ';
+#endif
+
   if (SkipOpers)
     return;