[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
diff --git a/llvm/lib/Analysis/DemandedBits.cpp b/llvm/lib/Analysis/DemandedBits.cpp
index 688c1db..151c0b0 100644
--- a/llvm/lib/Analysis/DemandedBits.cpp
+++ b/llvm/lib/Analysis/DemandedBits.cpp
@@ -110,6 +110,9 @@
// 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
