[clang] [clang-tools-extra] [llvm] Add out-of-line-atomics support to GlobalISel (PR #74588)

[Matt Arsenault via llvm-commits]

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@@ -765,6 +766,138 @@ llvm::createMemLibcall(MachineIRBuilder &MIRBuilder, MachineRegisterInfo &MRI,
   return LegalizerHelper::Legalized;
 }
 
+static RTLIB::Libcall getOutlineAtomicLibcall(MachineInstr &MI) {
+  unsigned Opc = MI.getOpcode();
+  auto &AtomicMI = cast<GMemOperation>(MI);
+  auto &MMO = AtomicMI.getMMO();
+  auto Ordering = MMO.getMergedOrdering();
+  LLT MemType = MMO.getMemoryType();
+  uint64_t MemSize = MemType.getSizeInBytes();
+  if (!MemType.isScalar())
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arsenm wrote:

Probably should check isVector, this will incorrectly bail for pointers 

https://github.com/llvm/llvm-project/pull/74588