[PATCH] D74484: [AggressiveInstCombine] Add support for ICmp instr that feeds a select intsr's condition operand.

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri added inline comments.


================
Comment at: llvm/lib/Transforms/AggressiveInstCombine/TruncInstCombine.cpp:173
+  // If the const value is signed and negative, count the leading ones.
+  APInt Val = C->getValue();
+  if (IsSigned && Val.isNegative())
----------------
Why copy?


================
Comment at: llvm/lib/Transforms/AggressiveInstCombine/TruncInstCombine.cpp:178
+  // Otherwise, count leading zeroes.
+  auto MinBits = Val.getBitWidth() - Val.countLeadingZeros();
+  return IsSigned ? MinBits + 1 : MinBits;
----------------
APInt::getActiveBits()


================
Comment at: llvm/lib/Transforms/AggressiveInstCombine/TruncInstCombine.cpp:180
+  return IsSigned ? MinBits + 1 : MinBits;
+}
+
----------------
Correct me if i'm wrong, but won't this just work?
```
static unsigned getConstMinBitWidth(bool IsSigned, ConstantInt *C) {
  const APInt& Val = C->getValue();
  unsigned NonSignBits = Val.getBitWidth() - Val.getNumSignBits();

  return IsSigned ? 1 + NonSignBits : NonSignBits;
}
```



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  https://reviews.llvm.org/D74484/new/

https://reviews.llvm.org/D74484