[llvm] [SCCP] Add support for trunc nuw range. (PR #152990)

[Yingwei Zheng via llvm-commits]

================
@@ -886,22 +887,36 @@ ConstantRange ConstantRange::truncate(uint32_t DstTySize) const {
   // We use the non-wrapped set code to analyze the [Lower, MaxValue) part, and
   // then we do the union with [MaxValue, Upper)
   if (isUpperWrapped()) {
-    // If Upper is greater than or equal to MaxValue(DstTy), it covers the whole
-    // truncated range.
-    if (Upper.getActiveBits() > DstTySize || Upper.countr_one() == DstTySize)
+    // If Upper is greater than MaxValue(DstTy), it covers the whole truncated
+    // range.
+    if (Upper.getActiveBits() > DstTySize)
       return getFull(DstTySize);
 
-    Union = ConstantRange(APInt::getMaxValue(DstTySize),Upper.trunc(DstTySize));
-    UpperDiv.setAllBits();
-
-    // Union covers the MaxValue case, so return if the remaining range is just
-    // MaxValue(DstTy).
-    if (LowerDiv == UpperDiv)
-      return Union;
+    // For nuw the two parts are: [0, Upper) \/ [Lower, MaxValue(DstTy) + 1]
----------------
dtcxzyw wrote:

```suggestion
    // For nuw the two parts are: [0, Upper) \/ [Lower, MaxValue(DstTy)]
```


https://github.com/llvm/llvm-project/pull/152990