[llvm] `__builtin.canonicalize` in common code (PR #142105)

[Dominik Steenken via llvm-commits]

================
@@ -3356,6 +3356,23 @@ bool SelectionDAGLegalize::ExpandNode(SDNode *Node) {
     Results.push_back(Op);
     break;
   }
+  case ISD::FCANONICALIZE: {
+    // This implements llvm.canonicalize.f* by multiplication with 1.0,
+    // as suggested in https://llvm.org/docs/LangRef.html#id2335.
----------------
dominik-steenken wrote:

>From what i understand, the point of the strictfp operation here is to prevent any optimization that would, for instance, recognize that `1.0 * x` can be converted to just `x`. So would this suffice as an addition to the comment?
```
// We use `STRICT_FMUL` here to prevent this operation from being optimized out.
```

https://github.com/llvm/llvm-project/pull/142105