propagate fast-math-flags on DAG nodes

After D10403, we had FMF in the DAG but disabled by default. Nick reported no crashing errors after some stress testing, 
so I enabled them at r243687. However, Escha soon notified us of a bug not covered by any in-tree regression tests: 
if we don't propagate the flags, we may fail to CSE DAG nodes because differing FMF causes them to not match. There is
one test case in this patch to prove that point.

This patch hopes to fix or leave a 'TODO' for all of the in-tree places where we create nodes that are FMF-capable. I 
did this by putting an assert in SelectionDAG.getNode() to find any FMF-capable node that was being created without FMF
( D11807 ). I then ran all regression tests and test-suite and confirmed that everything passes.

This patch exposes remaining work to get DAG FMF to be fully functional: (1) add the flags to non-binary nodes such as
FCMP, FMA and FNEG; (2) add the flags to intrinsics; (3) use the flags as conditions for transforms rather than the
current global settings.

Differential Revision: http://reviews.llvm.org/D12095

llvm-svn: 247815

1 files changed, 22 insertions, 15 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 3acf749bf3e..455fc90bce9 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -397,24 +397,21 @@ static void AddNodeIDOperands(FoldingSetNodeID &ID,
     ID.AddInteger(Op.getResNo());
   }
 }
+
 /// Add logical or fast math flag values to FoldingSetNodeID value.
 static void AddNodeIDFlags(FoldingSetNodeID &ID, unsigned Opcode,
                            const SDNodeFlags *Flags) {
-  if (!Flags || !isBinOpWithFlags(Opcode))
+  if (!isBinOpWithFlags(Opcode))
     return;
 
-  unsigned RawFlags = Flags->getRawFlags();
-  // If no flags are set, do not alter the ID. We must match the ID of nodes
-  // that were created without explicitly specifying flags. This also saves time
-  // and allows a gradual increase in API usage of the optional optimization
-  // flags.
-  if (RawFlags != 0)
-    ID.AddInteger(RawFlags);
+  unsigned RawFlags = 0;
+  if (Flags)
+    RawFlags = Flags->getRawFlags();
+  ID.AddInteger(RawFlags);
 }
 
 static void AddNodeIDFlags(FoldingSetNodeID &ID, const SDNode *N) {
-  if (auto *Node = dyn_cast<BinaryWithFlagsSDNode>(N))
-    AddNodeIDFlags(ID, Node->getOpcode(), &Node->Flags);
+  AddNodeIDFlags(ID, N->getOpcode(), N->getFlags());
 }
 
 static void AddNodeIDNode(FoldingSetNodeID &ID, unsigned short OpC,
@@ -3191,8 +3188,10 @@ SDValue SelectionDAG::getNode(unsigned Opcode, SDLoc DL,
   case ISD::FNEG:
     // -(X-Y) -> (Y-X) is unsafe because when X==Y, -0.0 != +0.0
     if (getTarget().Options.UnsafeFPMath && OpOpcode == ISD::FSUB)
+      // FIXME: FNEG has no fast-math-flags to propagate; use the FSUB's flags?
       return getNode(ISD::FSUB, DL, VT, Operand.getNode()->getOperand(1),
-                     Operand.getNode()->getOperand(0));
+                       Operand.getNode()->getOperand(0),
+                       &cast<BinaryWithFlagsSDNode>(Operand.getNode())->Flags);
     if (OpOpcode == ISD::FNEG)  // --X -> X
       return Operand.getNode()->getOperand(0);
     break;
@@ -5394,12 +5393,12 @@ SDValue SelectionDAG::getNode(unsigned Opcode, SDLoc DL, EVT VT,
 }
 
 SDValue SelectionDAG::getNode(unsigned Opcode, SDLoc DL, EVT VT,
-                              ArrayRef<SDValue> Ops) {
+                              ArrayRef<SDValue> Ops, const SDNodeFlags *Flags) {
   unsigned NumOps = Ops.size();
   switch (NumOps) {
   case 0: return getNode(Opcode, DL, VT);
   case 1: return getNode(Opcode, DL, VT, Ops[0]);
-  case 2: return getNode(Opcode, DL, VT, Ops[0], Ops[1]);
+  case 2: return getNode(Opcode, DL, VT, Ops[0], Ops[1], Flags);
   case 3: return getNode(Opcode, DL, VT, Ops[0], Ops[1], Ops[2]);
   default: break;
   }
@@ -6850,6 +6849,12 @@ uint64_t SDNode::getConstantOperandVal(unsigned Num) const {
   return cast<ConstantSDNode>(OperandList[Num])->getZExtValue();
 }
 
+const SDNodeFlags *SDNode::getFlags() const {
+  if (auto *FlagsNode = dyn_cast<BinaryWithFlagsSDNode>(this))
+    return &FlagsNode->Flags;
+  return nullptr;
+}
+
 SDValue SelectionDAG::UnrollVectorOp(SDNode *N, unsigned ResNE) {
   assert(N->getNumValues() == 1 &&
          "Can't unroll a vector with multiple results!");
@@ -6886,9 +6891,11 @@ SDValue SelectionDAG::UnrollVectorOp(SDNode *N, unsigned ResNE) {
     }
 
     switch (N->getOpcode()) {
-    default:
-      Scalars.push_back(getNode(N->getOpcode(), dl, EltVT, Operands));
+    default: {
+      Scalars.push_back(getNode(N->getOpcode(), dl, EltVT, Operands,
+                                N->getFlags()));
       break;
+    }
     case ISD::VSELECT:
       Scalars.push_back(getNode(ISD::SELECT, dl, EltVT, Operands));
       break;