[FPEnv] Add an option to disable strict float node mutating to an normal

float node

This patch add an option 'disable-strictnode-mutation' to prevent strict
node mutating to an normal node.
So we can make sure that the patch which sets strict-node as legal works
correctly.

Patch by Chen Liu(LiuChen3)

Differential Revision: https://reviews.llvm.org/D70226

include/llvm/CodeGen/TargetLowering.h

@@ -231,6 +231,11 @@ public:
   TargetLoweringBase &operator=(const TargetLoweringBase &) = delete;
   virtual ~TargetLoweringBase() = default;
 
+  /// Return true if the target support strict float operation
+  bool isStrictFPEnabled() const {
+    return IsStrictFPEnabled;
+  }
+
 protected:
   /// Initialize all of the actions to default values.
   void initActions();
@@ -2909,6 +2914,8 @@ protected:
   /// details.
   MachineBasicBlock *emitXRayTypedEvent(MachineInstr &MI,
                                         MachineBasicBlock *MBB) const;
+
+  bool IsStrictFPEnabled;
 };
 
 /// This class defines information used to lower LLVM code to legal SelectionDAG

lib/CodeGen/SelectionDAG/LegalizeDAG.cpp

@@ -2805,12 +2805,18 @@ bool SelectionDAGLegalize::ExpandNode(SDNode *Node) {
     break;
   }
   case ISD::STRICT_FP_ROUND:
-    // This expansion does not honor the "strict" properties anyway,
-    // so prefer falling back to the non-strict operation if legal.
+    // When strict mode is enforced we can't do expansion because it
+    // does not honor the "strict" properties. Only libcall is allowed.
+    if (TLI.isStrictFPEnabled())
+      break;
+    // We might as well mutate to FP_ROUND when FP_ROUND operation is legal
+    // since this operation is more efficient than stack operation.
     if (TLI.getStrictFPOperationAction(Node->getOpcode(),
                                        Node->getValueType(0))
         == TargetLowering::Legal)
       break;
+    // We fall back to use stack operation when the FP_ROUND operation
+    // isn't available.
     Tmp1 = EmitStackConvert(Node->getOperand(1), 
                             Node->getValueType(0),
                             Node->getValueType(0), dl, Node->getOperand(0));
@@ -2825,12 +2831,18 @@ bool SelectionDAGLegalize::ExpandNode(SDNode *Node) {
     Results.push_back(Tmp1);
     break;
   case ISD::STRICT_FP_EXTEND:
-    // This expansion does not honor the "strict" properties anyway,
-    // so prefer falling back to the non-strict operation if legal.
+    // When strict mode is enforced we can't do expansion because it
+    // does not honor the "strict" properties. Only libcall is allowed.
+    if (TLI.isStrictFPEnabled())
+      break;
+    // We might as well mutate to FP_EXTEND when FP_EXTEND operation is legal
+    // since this operation is more efficient than stack operation.
     if (TLI.getStrictFPOperationAction(Node->getOpcode(),
                                        Node->getValueType(0))
         == TargetLowering::Legal)
       break;
+    // We fall back to use stack operation when the FP_EXTEND operation
+    // isn't available.
     Tmp1 = EmitStackConvert(Node->getOperand(1),
                             Node->getOperand(1).getValueType(),
                             Node->getValueType(0), dl, Node->getOperand(0));
@@ -3701,7 +3713,7 @@ bool SelectionDAGLegalize::ExpandNode(SDNode *Node) {
     break;
   }
 
-  if (Results.empty() && Node->isStrictFPOpcode()) {
+  if (!TLI.isStrictFPEnabled() && Results.empty() && Node->isStrictFPOpcode()) {
     // FIXME: We were asked to expand a strict floating-point operation,
     // but there is currently no expansion implemented that would preserve
     // the "strict" properties.  For now, we just fall back to the non-strict

lib/CodeGen/SelectionDAG/LegalizeVectorOps.cpp

@@ -319,9 +319,9 @@ SDValue VectorLegalizer::LegalizeOp(SDValue Op) {
     // best approach, except in the case where the resulting strict (scalar)
     // operations would themselves use the fallback mutation to non-strict.
     // In that specific case, just do the fallback on the vector op.
-    if (Action == TargetLowering::Expand &&
+    if (Action == TargetLowering::Expand && !TLI.isStrictFPEnabled() &&
         TLI.getStrictFPOperationAction(Node->getOpcode(),
-                                       Node->getValueType(0))
+                                   Node->getValueType(0))
         == TargetLowering::Legal) {
       EVT EltVT = Node->getValueType(0).getVectorElementType();
       if (TLI.getOperationAction(Node->getOpcode(), EltVT)

lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp

@@ -1156,7 +1156,7 @@ void SelectionDAGISel::DoInstructionSelection() {
       // we convert them to normal FP opcodes instead at this point.  This
       // will allow them to be handled by existing target-specific instruction
       // selectors.
-      if (Node->isStrictFPOpcode() &&
+      if (!TLI->isStrictFPEnabled() && Node->isStrictFPOpcode() &&
           (TLI->getOperationAction(Node->getOpcode(), Node->getValueType(0))
            == TargetLowering::Expand))
         Node = CurDAG->mutateStrictFPToFP(Node);

lib/CodeGen/TargetLoweringBase.cpp

@@ -88,6 +88,14 @@ static cl::opt<unsigned> OptsizeJumpTableDensity(
     cl::desc("Minimum density for building a jump table in "
              "an optsize function"));
 
+// FIXME: This option is only to test if the strict fp operation processed
+// correctly by preventing mutating strict fp operation to normal fp operation
+// during development. When the backend supports strict float operation, this
+// option will be meaningless.
+static cl::opt<bool> DisableStrictNodeMutation("disable-strictnode-mutation",
+       cl::desc("Don't mutate strict-float node to a legalize node"),
+       cl::init(false), cl::Hidden);
+
 static bool darwinHasSinCos(const Triple &TT) {
   assert(TT.isOSDarwin() && "should be called with darwin triple");
   // Don't bother with 32 bit x86.
@@ -585,6 +593,7 @@ TargetLoweringBase::TargetLoweringBase(const TargetMachine &tm) : TM(tm) {
   BooleanVectorContents = UndefinedBooleanContent;
   SchedPreferenceInfo = Sched::ILP;
   GatherAllAliasesMaxDepth = 18;
+  IsStrictFPEnabled = DisableStrictNodeMutation;
   // TODO: the default will be switched to 0 in the next commit, along
   // with the Target-specific changes necessary.
   MaxAtomicSizeInBitsSupported = 1024;

lib/Target/SystemZ/SystemZISelLowering.cpp

@@ -634,6 +634,9 @@ SystemZTargetLowering::SystemZTargetLowering(const TargetMachine &TM,
   // than "STC;MVC".  Handle the choice in target-specific code instead.
   MaxStoresPerMemset = 0;
   MaxStoresPerMemsetOptSize = 0;
+
+  // Default to having -disable-strictnode-mutation on
+  IsStrictFPEnabled = true;
 }
 
 EVT SystemZTargetLowering::getSetCCResultType(const DataLayout &DL,