[Alignment][NFC] Simplify IRTranslator::getMemOpAlignment

[gchatelet]

Summary

This is patch is part of a series to introduce an Alignment type.
See this thread for context: http://lists.llvm.org/pipermail/llvm-dev/2019-July/133851.html
See this patch for the introduction of the type: https://reviews.llvm.org/D64790

[courbet]

llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp

246–247

you can now remove all the else if statements:

if (const StoreInst *SI = dyn_cast<StoreInst>(&I)) {
  return ...;
}
if (...) {
  return ...;
}

[gchatelet]

• Address comments

llvm/include/llvm/CodeGen/GlobalISel/IRTranslator.h

private:
 
   /// Get the frame index that represents \p Val.
   /// If such VReg does not exist, it is created.
   int getOrCreateFrameIndex(const AllocaInst &AI);
 
   /// Get the alignment of the given memory operation instruction. This will
   /// either be the explicitly specified value or the ABI-required alignment for
   /// the type being accessed (according to the Module's DataLayout).
-  unsigned getMemOpAlignment(const Instruction &I);
+  /// FIXME: Remove once transition to Align is over.
+  inline unsigned getMemOpAlignment(const Instruction &I) {
+    return getMemOpAlign(I).value();
+  }
+
+  /// Get the alignment of the given memory operation instruction. This will
+  /// either be the explicitly specified value or the ABI-required alignment for
+  /// the type being accessed (according to the Module's DataLayout).
+  Align getMemOpAlign(const Instruction &I);
 
   /// Get the MachineBasicBlock that represents \p BB. Specifically, the block
   /// returned will be the head of the translated block (suitable for branch
   /// destinations).
   MachineBasicBlock &getMBB(const BasicBlock &BB);
 
   /// Record \p NewPred as a Machine predecessor to `Edge.second`, corresponding
   /// to `Edge.first` at the IR level. This is used when IRTranslation creates

llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp

int IRTranslator::getOrCreateFrameIndex(const AllocaInst &AI) {
   if (!Alignment)
     Alignment = DL->getABITypeAlignment(AI.getAllocatedType());
 
   int &FI = FrameIndices[&AI];
   FI = MF->getFrameInfo().CreateStackObject(Size, Alignment, false, &AI);
   return FI;
 }
 
-unsigned IRTranslator::getMemOpAlignment(const Instruction &I) {
-  unsigned Alignment = 0;
-  Type *ValTy = nullptr;
+Align IRTranslator::getMemOpAlign(const Instruction &I) {
   if (const StoreInst *SI = dyn_cast<StoreInst>(&I)) {
-    Alignment = SI->getAlignment();
-    ValTy = SI->getValueOperand()->getType();
-  } else if (const LoadInst *LI = dyn_cast<LoadInst>(&I)) {
-    Alignment = LI->getAlignment();
-    ValTy = LI->getType();
-  } else if (const AtomicCmpXchgInst *AI = dyn_cast<AtomicCmpXchgInst>(&I)) {
+    Type *ValTy = SI->getValueOperand()->getType();
+    return SI->getAlign().getValueOr(DL->getABITypeAlign(ValTy));
+  }
+  if (const LoadInst *LI = dyn_cast<LoadInst>(&I)) {
+    Type *ValTy = LI->getType();
+    return LI->getAlign().getValueOr(DL->getABITypeAlign(ValTy));
+  }
+  if (const AtomicCmpXchgInst *AI = dyn_cast<AtomicCmpXchgInst>(&I)) {
     // TODO(PR27168): This instruction has no alignment attribute, but unlike
     // the default alignment for load/store, the default here is to assume
     // it has NATURAL alignment, not DataLayout-specified alignment.
     const DataLayout &DL = AI->getModule()->getDataLayout();
-    Alignment = DL.getTypeStoreSize(AI->getCompareOperand()->getType());
-    ValTy = AI->getCompareOperand()->getType();
-  } else if (const AtomicRMWInst *AI = dyn_cast<AtomicRMWInst>(&I)) {
+    return Align(DL.getTypeStoreSize(AI->getCompareOperand()->getType()));
+  }
+  if (const AtomicRMWInst *AI = dyn_cast<AtomicRMWInst>(&I)) {
     // TODO(PR27168): This instruction has no alignment attribute, but unlike
     // the default alignment for load/store, the default here is to assume
     // it has NATURAL alignment, not DataLayout-specified alignment.
     const DataLayout &DL = AI->getModule()->getDataLayout();
-    Alignment = DL.getTypeStoreSize(AI->getValOperand()->getType());
-    ValTy = AI->getType();
-  } else {
-    OptimizationRemarkMissed R("gisel-irtranslator", "", &I);
-    R << "unable to translate memop: " << ore::NV("Opcode", &I);
-    reportTranslationError(*MF, *TPC, *ORE, R);
-    return 1;
-  }
-
-  return Alignment ? Alignment : DL->getABITypeAlignment(ValTy);
+    return Align(DL.getTypeStoreSize(AI->getValOperand()->getType()));
+  }
+  return Align(1);
 }
 
 MachineBasicBlock &IRTranslator::getMBB(const BasicBlock &BB) {
   MachineBasicBlock *&MBB = BBToMBB[&BB];
   assert(MBB && "BasicBlock was not encountered before");
   return *MBB;
 }