[llvm] [ARM] Use correct ABI for atomic functions (PR #128891)

[Matt Arsenault via llvm-commits]

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@@ -1999,6 +1999,19 @@ bool AtomicExpandImpl::expandAtomicOpToLibcall(
       Value *IntValue =
           Builder.CreateBitOrPointerCast(ValueOperand, SizedIntTy);
       Args.push_back(IntValue);
+
+      // Set the zeroext/signext attributes on the parameter if needed to match
+      // the target's ABI.
+      if (TLI->shouldExtendTypeInLibCall(
+              TLI->getMemValueType(DL, SizedIntTy))) {
+        // The only atomic operations affected by signedness are min/max, and
+        // we don't have __atomic_ libcalls for them, so IsSigned is always
+        // false.
+        if (TLI->shouldSignExtendTypeInLibCall(SizedIntTy, false /*IsSigned*/))
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arsenm wrote:

This is using 3 levels of terrible TargetLowering API. Really we should be able to query the signature of the specific libcall from RuntimeLibcalls, not these global overrides. 

The part I understand least is why you need getMemValueType

https://github.com/llvm/llvm-project/pull/128891