[Analysis] Support bitreverse in -demanded-bits pass

Summary:
* Add a bitreverse case in the demanded bits analysis pass.
* Add tests for the bitreverse (and bswap) intrinsic in the
  demanded bits pass.
* Add a test case to the BDCE tests: that manipulations to
  high-order bits are eliminated once the bits are reversed
  and then right-shifted.

Reviewers: mkuper, jmolloy, hfinkel, trentxintong

Reviewed By: jmolloy

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D31857

llvm-svn: 300215

1 files changed, 3 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/DemandedBits.cpp b/llvm/lib/Analysis/DemandedBits.cpp
index 688c1db534c..151c0b0e6c9 100644
--- a/llvm/lib/Analysis/DemandedBits.cpp
+++ b/llvm/lib/Analysis/DemandedBits.cpp
@@ -110,6 +110,9 @@ void DemandedBits::determineLiveOperandBits(
         // the output.
         AB = AOut.byteSwap();
         break;
+      case Intrinsic::bitreverse:
+        AB = AOut.reverseBits();
+        break;
       case Intrinsic::ctlz:
         if (OperandNo == 0) {
           // We need some output bits, so we need all bits of the