[Alignment][NFC] Add a helper function to DataLayout

[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

llvm/include/llvm/IR/DataLayout.h

public:
   /// returns 96 or 128 for x86_fp80, depending on alignment.
   TypeSize getTypeAllocSizeInBits(Type *Ty) const {
     return 8 * getTypeAllocSize(Ty);
   }
 
   /// Returns the minimum ABI-required alignment for the specified type.
   unsigned getABITypeAlignment(Type *Ty) const;
 
+  /// Helper function to return `Alignment` if it's set or the result of
+  /// `getABITypeAlignment(Ty)`, in any case the result is a valid alignment.
+  inline Align getValueOrABITypeAlignment(MaybeAlign Alignment,
+                                          Type *Ty) const {
+    return Alignment ? *Alignment : Align(getABITypeAlignment(Ty));
+  }
+
   /// Returns the minimum ABI-required alignment for an integer type of
   /// the specified bitwidth.
   Align getABIIntegerTypeAlignment(unsigned BitWidth) const;
 
   /// Returns the preferred stack/global alignment for the specified
   /// type.
   ///
   /// This is always at least as good as the ABI alignment.

llvm/unittests/IR/DataLayoutTest.cpp

 //===- ConstantRangeTest.cpp - ConstantRange tests ------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "llvm/IR/DataLayout.h"
+#include "llvm/IR/LLVMContext.h"
+#include "llvm/IR/Type.h"
 #include "gtest/gtest.h"
 
 using namespace llvm;
 
 namespace {
 
 TEST(DataLayoutTest, FunctionPtrAlign) {
   EXPECT_EQ(MaybeAlign(0), DataLayout("").getFunctionPtrAlign());
TEST(DataLayoutTest, FunctionPtrAlign) {
   EXPECT_NE(b, c);
 
   a = b;
   EXPECT_EQ(a, b);
   a = c;
   EXPECT_EQ(a, c);
 }
 
+TEST(DataLayoutTest, ValueOrABITypeAlignment) {
+  const DataLayout DL("Fi8");
+  LLVMContext Context;
+  Type *const FourByteAlignType = Type::getInt32Ty(Context);
+  EXPECT_EQ(Align(16),
+            DL.getValueOrABITypeAlignment(MaybeAlign(16), FourByteAlignType));
+  EXPECT_EQ(Align(4),
+            DL.getValueOrABITypeAlignment(MaybeAlign(), FourByteAlignType));
+}
+
 }  // anonymous namespace