[LLVM][Alignment] Fix MSVC warning

[RKSimon]

Summary

https://bugs.llvm.org/show_bug.cgi?id=42911

[RKSimon]

This isn't handling all the cases - its probably better to push at the top of the file (before namespace) and similarly pop at the end of the file

[gchatelet]

In D65859#1629358, @RKSimon wrote:

This isn't handling all the cases - its probably better to push at the top of the file (before namespace) and similarly pop at the end of the file

Thx Simon, I'm OOO right now and traveling next week. Would you have a chance to check that the fix you offer is fixing the Windows build?

[RKSimon]

Disable MSVC divide by zero warnings for the whole of AlignmentTest.cpp

[RKSimon]

Adding some people interested in MSVC builds

[gbedwell]

I've not tested, but it seems reasonable. The only other "#pragma warning" I came across (in the neighbouring llvm/unittests/Support/AlignOfTest.cpp) doesn't bother with a push/pop and just disables the warnings at file scope. I'm not sure if there's any reason to push/pop across the entire file unless we think we might want to ever include this cpp file inside another one?

[RKSimon]

I'm happy to remove the push/pull if reviewers prefer - its just a personal style preference tbh

[rnk]

lgtm

I prefer push/pop generally.

[gbedwell]

In D65859#1631409, @RKSimon wrote:

I'm happy to remove the push/pull if reviewers prefer - its just a personal style preference tbh

I have no strong preference. LGTM either way.

[gchatelet]

LGTM.
Thx for fixing it!

llvm/trunk/unittests/Support/AlignmentTest.cpp

 //=== - llvm/unittest/Support/Alignment.cpp - Alignment utility 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/Support/Alignment.h"
 #include "gtest/gtest.h"
 
 #include <vector>
 
+#ifdef _MSC_VER
+// Disable warnings about potential divide by 0.
+#pragma warning(push)
+#pragma warning(disable : 4723)
+#endif
+
 using namespace llvm;
 
 namespace {
 
 std::vector<uint64_t> getValidAlignments() {
   std::vector<uint64_t> Out;
   for (size_t Shift = 0; Shift < 64; ++Shift)
     Out.push_back(1ULL << Shift);
for (uint64_t Value : getValidAlignmentsForDeathTest()) {
     EXPECT_DEATH((void)(Align(Value) > MaybeAlign(0)), ".* should be defined");
     EXPECT_DEATH((void)(Align(Value) < MaybeAlign(0)), ".* should be defined");
   }
 }
 
 #endif // NDEBUG
 
 } // end anonymous namespace
+
+#ifdef _MSC_VER
+#pragma warning(pop)
+#endif