[AIX] Suppress -Waix-compat warning with SmallVector class

[Jake-Egan]

Summary

When building LLVM with Open XL and -Werror is specified, the -Waix-compat warning becomes an error. This patch updates the SmallVector class to suppress the -Waix-compat warning/error on AIX.

[Jake-Egan]

Add condition for _AIX.

[daltenty]

Not sure the compilers in question accept this attribute form.

Since this structure is only used for checking the following static asserts, so binary compat probably isn't a real concern. So maybe it's better to suppress the warning is better this case.

[Jake-Egan]

Suppress -Waix-compat warning

[daltenty]

LGTM, with minor nit

llvm/lib/Support/SmallVector.cpp

22

nit: maybe a comment would be warranted, since this what the intention of this is won't be very obvious to anyone who doesn't work on AIX

[Jake-Egan]

Added a comment.

llvm/lib/Support/SmallVector.cpp

 #include <cstdint>
 #ifdef LLVM_ENABLE_EXCEPTIONS
 #include <stdexcept>
 #endif
 using namespace llvm;
 
 // Check that no bytes are wasted and everything is well-aligned.
 namespace {
+// These structures may cause binary compat warnings on AIX. Suppress the
+// warning since we are only using these types for the static assertions below.
+#if defined(_AIX)
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Waix-compat"
+#endif
 struct Struct16B {
   alignas(16) void *X;
 };
 struct Struct32B {
   alignas(32) void *X;
 };
+#if defined(_AIX)
+#pragma GCC diagnostic pop
+#endif
 }
 static_assert(sizeof(SmallVector<void *, 0>) ==
                   sizeof(unsigned) * 2 + sizeof(void *),
               "wasted space in SmallVector size 0");
 static_assert(alignof(SmallVector<Struct16B, 0>) >= alignof(Struct16B),
               "wrong alignment for 16-byte aligned T");
 static_assert(alignof(SmallVector<Struct32B, 0>) >= alignof(Struct32B),
               "wrong alignment for 32-byte aligned T");