[DEBUGINFO] Handle restore instructions in LiveDebugValues

The LiveDebugValues pass recognizes spills but not restores, which can 
cause large gaps in location information for some variables, depending
on control flow. This patch make LiveDebugValues recognize restores and
generate appropriate DBG_VALUE instructions. 

Reviewers: aprantl, NicolaPrica

Differential Revision: https://reviews.llvm.org/D57271

llvm-svn: 352642

Author: wolfy1961

llvm/include/llvm/CodeGen/MachineInstr.h

@@ -1399,6 +1399,19 @@ class MachineInstr
   /// Return true if all the defs of this instruction are dead.
   bool allDefsAreDead() const;
 
+  /// Return a valid size if the instruction is a spill instruction.
+  Optional<unsigned> getSpillSize(const TargetInstrInfo *TII) const;
+
+  /// Return a valid size if the instruction is a folded spill instruction.
+  Optional<unsigned> getFoldedSpillSize(const TargetInstrInfo *TII) const;
+
+  /// Return a valid size if the instruction is a restore instruction.
+  Optional<unsigned> getRestoreSize(const TargetInstrInfo *TII) const;
+
+  /// Return a valid size if the instruction is a folded restore instruction.
+  Optional<unsigned>
+  getFoldedRestoreSize(const TargetInstrInfo *TII) const;
+
   /// Copy implicit register operands from specified
   /// instruction to this instruction.
   void copyImplicitOps(MachineFunction &MF, const MachineInstr &MI);

llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp

@@ -754,46 +754,25 @@ static bool emitComments(const MachineInstr &MI, raw_ostream &CommentOS,
   const TargetInstrInfo *TII = MF->getSubtarget().getInstrInfo();
 
   // Check for spills and reloads
-  int FI;
-
-  const MachineFrameInfo &MFI = MF->getFrameInfo();
   bool Commented = false;
 
-  auto getSize =
-      [&MFI](const SmallVectorImpl<const MachineMemOperand *> &Accesses) {
-        unsigned Size = 0;
-        for (auto A : Accesses)
-          if (MFI.isSpillSlotObjectIndex(
-                  cast<FixedStackPseudoSourceValue>(A->getPseudoValue())
-                      ->getFrameIndex()))
-            Size += A->getSize();
-        return Size;
-      };
-
   // We assume a single instruction only has a spill or reload, not
   // both.
-  const MachineMemOperand *MMO;
-  SmallVector<const MachineMemOperand *, 2> Accesses;
-  if (TII->isLoadFromStackSlotPostFE(MI, FI)) {
-    if (MFI.isSpillSlotObjectIndex(FI)) {
-      MMO = *MI.memoperands_begin();
-      CommentOS << MMO->getSize() << "-byte Reload";
-      Commented = true;
-    }
-  } else if (TII->hasLoadFromStackSlot(MI, Accesses)) {
-    if (auto Size = getSize(Accesses)) {
-      CommentOS << Size << "-byte Folded Reload";
-      Commented = true;
-    }
-  } else if (TII->isStoreToStackSlotPostFE(MI, FI)) {
-    if (MFI.isSpillSlotObjectIndex(FI)) {
-      MMO = *MI.memoperands_begin();
-      CommentOS << MMO->getSize() << "-byte Spill";
+  Optional<unsigned> Size;
+  if ((Size = MI.getRestoreSize(TII))) {
+    CommentOS << *Size << "-byte Reload";
+    Commented = true;
+  } else if ((Size = MI.getFoldedRestoreSize(TII))) {
+    if (*Size) {
+      CommentOS << *Size << "-byte Folded Reload";
       Commented = true;
     }
-  } else if (TII->hasStoreToStackSlot(MI, Accesses)) {
-    if (auto Size = getSize(Accesses)) {
-      CommentOS << Size << "-byte Folded Spill";
+  } else if ((Size = MI.getSpillSize(TII))) {
+    CommentOS << *Size << "-byte Spill";
+    Commented = true;
+  } else if ((Size = MI.getFoldedSpillSize(TII))) {
+    if (*Size) {
+      CommentOS << *Size << "-byte Folded Spill";
       Commented = true;
     }
   }