[PATCH] D34029: Infer lowest bits of an integer Multiply when the low bits of the operands are known

Eli Friedman via Phabricator via llvm-commits llvm-commits at lists.llvm.org
Fri Jul 28 17:28:31 PDT 2017

efriedma added inline comments.

Comment at: lib/Analysis/ValueTracking.cpp:377
+  unsigned ResultBitsKnown = std::min(TrailBitsKnown0 - TrailZero0,
+                                      TrailBitsKnown1 - TrailZero1);
+  // We know at least the trailing zeros, plus any other known bits
Reusing the name ResultBitsKnown is confusing.

Comment at: lib/Analysis/ValueTracking.cpp:380
+  // of the operands.
+  ResultBitsKnown = std::min(ResultBitsKnown + TrailZ, BitWidth);
These little comments aren't that useful for understanding the logic; needs one big paragraph explaining the logic for computing ResultBitsKnown.


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