[PATCH] D142271: [ValueTracking] Add KnownBits patterns `xor(x, x - 1)` and `and(x, -x)` for knowing upper bits to be zero

[Nikita Popov via Phabricator via llvm-commits]

nikic added inline comments.


================
Comment at: llvm/lib/Analysis/ValueTracking.cpp:1136
+        C->isAllOnes()) {
+      const KnownBits &XBits = I->getOperand(0) == X ? Known2 : Known;
+      Known = XBits.blsmsk();
----------------
nikic wrote:
> Shouldn't this be `? Known : Known2`? We want the known bits of X, not of X-1.
Ignore this comment, the variable naming is a bit confusing here.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D142271/new/

https://reviews.llvm.org/D142271