fix for PR20354 - Miscompile of fabs due to vectorization

This is intended to be the minimal change needed to fix PR20354 ( http://llvm.org/bugs/show_bug.cgi?id=20354 ). The check for a vector operation was wrong; we need to check that the fabs itself is not a vector operation.

This patch will not generate the optimal code. A constant pool load and 'and' op will be generated instead of just returning a value that we can calculate in advance (as we do for the scalar case). I've put a 'TODO' comment for that here and expect to have that patch ready soon.

There is a very similar optimization that we can do in visitFNEG, so I've put another 'TODO' there and expect to have another patch for that too.

llvm-svn: 214670

1 files changed, 5 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index b8baaadffcd..e6b6c9f5e8d 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -7311,6 +7311,8 @@ SDValue DAGCombiner::visitFNEG(SDNode *N) {
 
   // Transform fneg(bitconvert(x)) -> bitconvert(x^sign) to avoid loading
   // constant pool values.
+  // TODO: We can also optimize for vectors here, but we need to make sure
+  // that the sign mask is created properly for each vector element.
   if (!TLI.isFNegFree(VT) && N0.getOpcode() == ISD::BITCAST &&
       !VT.isVector() &&
       N0.getNode()->hasOneUse() &&
@@ -7403,10 +7405,12 @@ SDValue DAGCombiner::visitFABS(SDNode *N) {
 
   // Transform fabs(bitconvert(x)) -> bitconvert(x&~sign) to avoid loading
   // constant pool values.
+  // TODO: We can also optimize for vectors here, but we need to make sure
+  // that the sign mask is created properly for each vector element.
   if (!TLI.isFAbsFree(VT) &&
       N0.getOpcode() == ISD::BITCAST && N0.getNode()->hasOneUse() &&
       N0.getOperand(0).getValueType().isInteger() &&
-      !N0.getOperand(0).getValueType().isVector()) {
+      !VT.isVector()) {
     SDValue Int = N0.getOperand(0);
     EVT IntVT = Int.getValueType();
     if (IntVT.isInteger() && !IntVT.isVector()) {