[PATCH] D69960: [ConstantRange] Add `ushl_sat()`/`sshl_sat()` methods.

[Nikita Popov via Phabricator via llvm-commits]

nikic added a comment.

> Unlike ConstantRange::shl(), these are precise.

At least when modelling the APInt semantics. If we treat too large shifts as poison, then we could produce empty sets in more cases. But this seems like a reasonable starting point...



================
Comment at: llvm/lib/IR/ConstantRange.cpp:1359
+    NewU = getSignedMax().sshl_sat(Other.getUnsignedMax()) + 1;
+  }
+  return getNonEmpty(std::move(NewL), std::move(NewU));
----------------
Wondering if a formulation along the lines of

```
APInt Min = getSignedMin(), Max = getSignedMax();
APInt ShiftMin = getUnsignedMin(), ShiftMax = getUnsignedMax();
APInt NewL = Min.sshl_sat(Min.isNonNegative() ? ShiftMin : ShiftMax);
APInt NewU = Max.sshl_sat(Max.isNonNegative() ? ShiftMax : ShiftMin) + 1;
```

might be cleaner?


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https://reviews.llvm.org/D69960