[llvm] [DAGCombiner] Handle type-promoted constants in UDIV lowering (PR #169491)

[David Green via llvm-commits]

================
@@ -1076,9 +1077,17 @@ static bool isConstantOrConstantVector(SDValue N, bool NoOpaques = false) {
     if (Op.isUndef())
       continue;
     ConstantSDNode *Const = dyn_cast<ConstantSDNode>(Op);
-    if (!Const || Const->getAPIntValue().getBitWidth() != BitWidth ||
-        (Const->isOpaque() && NoOpaques))
+    if (!Const || (Const->isOpaque() && NoOpaques))
       return false;
+    // When AllowTruncation is true, allow constants that have been promoted
+    // during type legalization as long as the value fits in the target type.
+    if (AllowTruncation) {
+      if (Const->getAPIntValue().getActiveBits() > BitWidth)
+        return false;
+    } else {
+      if (Const->getAPIntValue().getBitWidth() != BitWidth)
+        return false;
+    }
----------------
davemgreen wrote:

```
    if ((AllowTruncation && Const->getAPIntValue().getActiveBits() > BitWidth) ||
        (!AllowTruncation && Const->getAPIntValue().getActiveBits() != BitWidth))
      return false;
```

https://github.com/llvm/llvm-project/pull/169491