Fix KeyPath failure on s390x

[levivic]

This is to change the tuple metadata to use a 32-bit offset to address the failure seen in KeyPath test on big-endian platform (s390x). Details of the issue and discussion can be found at https://forums.swift.org/t/keypath-issue-with-s390x/24473

[levivic]

Hi, @jckarter, as we discussed in https://forums.swift.org/t/keypath-issue-with-s390x/24473, can you please review this PR? I have also got another related PR #25329 outstanding. Any feedback on that one will be appreciated as well.

[jckarter]

Looks good! For ABI compatibility on Apple platforms, we'd want to conditionalize this, because existing binaries will try to load the full 64 bits, and we want to keep those zeroed:

#if __APPLE__
  StoredSize Offset;
#else
  uint32_t Offset;
#endif

I think the IRGen side is fine, though, because in practice nobody is going to have a 4GB tuple (they'll run into other practical limits first), and new binaries doing a 32-bit little-endian load of the 64-bit field should be safe, and would open the door to us possibly being able to drop this compatibility hack in time.

[levivic]

@jckarter Change made. Thanks.

[jckarter]

@swift-ci Please test

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - a8149941f4fba5012c143e7dda07313b9ce9b3d5

[swift-ci]

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Swift Test Linux Platform
Git Sha - a8149941f4fba5012c143e7dda07313b9ce9b3d5

[mundaym]

@swift-ci Please test

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - c151d8bc320fc6a2c022d25285462ed3000d6b8b

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - c151d8bc320fc6a2c022d25285462ed3000d6b8b

[jckarter]

Looks like a test needs to be updated:

/Users/buildnode/jenkins/workspace/swift-PR-osx/branch-master/swift/test/IRGen/generic_tuples.swift:12:11: error: CHECK: expected string not found in input
08:03:46 // CHECK: %swift.tuple_element_type = type { [[TYPE]]*, i64 }
08:03:46           ^
08:03:46 <stdin>:19:1: note: scanning from here
08:03:46 %swift.tuple_element_type = type { %swift.type*, i32 }
08:03:46 ^
08:03:46 <stdin>:19:1: note: with variable "TYPE" equal to "%swift.type"
08:03:46 %swift.tuple_element_type = type { %swift.type*, i32 }
08:03:46 ^

[levivic]

@jckarter , yes, i have just updated the test.

[jckarter]

@swift-ci Please test

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - c151d8bc320fc6a2c022d25285462ed3000d6b8b

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - c151d8bc320fc6a2c022d25285462ed3000d6b8b