Extend known bits to understand @llvm.bswap

This is a cleaned up patch from the one written by John Regehr based on the findings of the Souper superoptimizer.

When writing tests, I was surprised to find that instsimplify apparently doesn't know how to collapse bit test sequences based purely on known bits. This required me to split my tests across both instsimplify and instcombine.

Differential Revision: http://reviews.llvm.org/D13250

llvm-svn: 249453

1 files changed, 6 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index f0b04b7133d..d3723037dda 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -1358,6 +1358,12 @@ static void computeKnownBitsFromOperator(Operator *I, APInt &KnownZero,
     if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
       switch (II->getIntrinsicID()) {
       default: break;
+      case Intrinsic::bswap:
+        computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, DL,
+                         Depth + 1, Q);
+        KnownZero |= KnownZero2.byteSwap();
+        KnownOne |= KnownOne2.byteSwap();
+        break;
       case Intrinsic::ctlz:
       case Intrinsic::cttz: {
         unsigned LowBits = Log2_32(BitWidth)+1;