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Fixes a problem in instruction selection with testing whether or not the

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transformation:

(X op C1) ^ C2 --> (X op C1) & ~C2 iff (C1&C2) == C2

should be done.  

This change has been tested:
 Using a debug+asserts build:
   on the specific test case that brought this bug to light
   make check-all
   lnt nt
   using this clang to build a release version of clang
 Using the release+asserts clang-with-clang build:
   on the specific test case that brought this bug to light
   make check-all
   lnt nt

Checking in because Evan wants it checked in.  Test case forthcoming after
scrubbing.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@154955 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Joel Jones 2012-04-17 22:23:10 +00:00
parent 3f5966b85e
commit d16ce17711
1 changed files with 3 additions and 2 deletions
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5
lib/CodeGen/SelectionDAG/TargetLowering.cpp
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@ -1367,8 +1367,9 @@ bool TargetLowering::SimplifyDemandedBits(SDValue Op,
// bits on that side are also known to be set on the other side, turn this
// into an AND, as we know the bits will be cleared.
// e.g. (X | C1) ^ C2 --> (X | C1) & ~C2 iff (C1&C2) == C2
if ((NewMask & (KnownZero|KnownOne)) == NewMask) { // all known
if ((KnownOne & KnownOne2) == KnownOne) {
// NB: it is okay if more bits are known than are requested
if ((NewMask & (KnownZero|KnownOne)) == NewMask) { // all known on one side
if (KnownOne == KnownOne2) { // set bits are the same on both sides
EVT VT = Op.getValueType();
SDValue ANDC = TLO.DAG.getConstant(~KnownOne & NewMask, VT);
return TLO.CombineTo(Op, TLO.DAG.getNode(ISD::AND, dl, VT,