[clang] [CIR] Upstream DivOp for ComplexType (PR #153796)

[Andy Kaylor via cfe-commits]

================
@@ -3013,6 +3013,47 @@ def CIR_ComplexMulOp : CIR_Op<"complex.mul", [
   }];
 }
 
+def CIR_ComplexDivOp : CIR_Op<"complex.div", [
+  Pure, SameOperandsAndResultType
+]> {
+  let summary = "Complex division";
+  let description = [{
+    The `cir.complex.div` operation takes two complex numbers and returns
+    their quotient.
+
+    The `range` attribute is used to select the algorithm used when
+    the operation is lowered to the LLVM dialect. For division, 'improved'
+    producing the Smith's algorithms for Complex division with no special
+    handling for NaN values. If 'promoted' is used, the values are promoted
+    to a higher precision type, if possible,  and the calculation is performed
+    using the algebraic formula. We only fall back on Smith's algorithm when
+    the target does not support a higher precision type. Also, this only
+    applies to floating-point types with no special handling for NaN values.
----------------
andykaylor wrote:

```suggestion
    using the algebraic formula, with no additional handling for NaN values.
    We fall back on Smith's algorithm when the target does not support a
    higher precision type. 
```
The comment about floating-point types applies to this entire paragraph. For integer types, the `range` attribute is ignored and we always lower to the algebraic formula. It's probably best to say that in a separate paragraph.

https://github.com/llvm/llvm-project/pull/153796