[Strict FP] Allow custom operation actions

This patch changes the DAG legalizer to respect the operation actions
set by the target for strict floating-point operations. (Currently, the
legalizer will usually fall back to mutate to the non-strict action
(which is assumed to be legal), and only skip mutation if the strict
operation is marked legal.)

With this patch, if whenever a strict operation is marked as Legal or
Custom, it is passed to the target as usual. Only if it is marked as
Expand will the legalizer attempt to mutate to the non-strict operation.
Note that this will now fail if the non-strict operation is itself
marked as Custom -- the target will have to provide a Custom definition
for the strict operation then as well.

Reviewed By: hfinkel

Differential Revision: https://reviews.llvm.org/D65226

llvm-svn: 368012

2 files changed, 41 insertions, 39 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
index bf817f00f83..e1775d5cb53 100644
--- a/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
@@ -1097,39 +1097,6 @@ void SelectionDAGLegalize::LegalizeOp(SDNode *Node) {
       return;
     }
     break;
-  case ISD::STRICT_FADD:
-  case ISD::STRICT_FSUB:
-  case ISD::STRICT_FMUL:
-  case ISD::STRICT_FDIV:
-  case ISD::STRICT_FREM:
-  case ISD::STRICT_FSQRT:
-  case ISD::STRICT_FMA:
-  case ISD::STRICT_FPOW:
-  case ISD::STRICT_FPOWI:
-  case ISD::STRICT_FSIN:
-  case ISD::STRICT_FCOS:
-  case ISD::STRICT_FEXP:
-  case ISD::STRICT_FEXP2:
-  case ISD::STRICT_FLOG:
-  case ISD::STRICT_FLOG10:
-  case ISD::STRICT_FLOG2:
-  case ISD::STRICT_FRINT:
-  case ISD::STRICT_FNEARBYINT:
-  case ISD::STRICT_FMAXNUM:
-  case ISD::STRICT_FMINNUM:
-  case ISD::STRICT_FCEIL:
-  case ISD::STRICT_FFLOOR:
-  case ISD::STRICT_FROUND:
-  case ISD::STRICT_FTRUNC:
-  case ISD::STRICT_FP_ROUND:
-  case ISD::STRICT_FP_EXTEND:
-    // These pseudo-ops get legalized as if they were their non-strict
-    // equivalent.  For instance, if ISD::FSQRT is legal then ISD::STRICT_FSQRT
-    // is also legal, but if ISD::FSQRT requires expansion then so does
-    // ISD::STRICT_FSQRT.
-    Action = TLI.getStrictFPOperationAction(Node->getOpcode(),
-                                            Node->getValueType(0));
-    break;
   case ISD::SADDSAT:
   case ISD::UADDSAT:
   case ISD::SSUBSAT:
@@ -2815,6 +2782,12 @@ 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.
+    if (TLI.getStrictFPOperationAction(Node->getOpcode(),
+                                       Node->getValueType(0))
+        == TargetLowering::Legal)
+      break;
     Tmp1 = EmitStackConvert(Node->getOperand(1), 
                             Node->getValueType(0),
                             Node->getValueType(0), dl, Node->getOperand(0));
@@ -2829,6 +2802,12 @@ 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.
+    if (TLI.getStrictFPOperationAction(Node->getOpcode(),
+                                       Node->getValueType(0))
+        == TargetLowering::Legal)
+      break;
     Tmp1 = EmitStackConvert(Node->getOperand(1),
                             Node->getOperand(1).getValueType(),
                             Node->getValueType(0), dl, Node->getOperand(0));
@@ -3715,6 +3694,18 @@ bool SelectionDAGLegalize::ExpandNode(SDNode *Node) {
     break;
   }
 
+  if (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
+    // version if that is legal on the target.  The actual mutation of the
+    // operation will happen in SelectionDAGISel::DoInstructionSelection.
+    if (TLI.getStrictFPOperationAction(Node->getOpcode(),
+                                       Node->getValueType(0))
+        == TargetLowering::Legal)
+      return true;
+  }
+
   // Replace the original node with the legalized result.
   if (Results.empty()) {
     LLVM_DEBUG(dbgs() << "Cannot expand node\n");
diff --git a/llvm/lib/CodeGen/SelectionDAG/LegalizeVectorOps.cpp b/llvm/lib/CodeGen/SelectionDAG/LegalizeVectorOps.cpp
index 10b8b705869..09b22215173 100644
--- a/llvm/lib/CodeGen/SelectionDAG/LegalizeVectorOps.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/LegalizeVectorOps.cpp
@@ -335,12 +335,23 @@ SDValue VectorLegalizer::LegalizeOp(SDValue Op) {
   case ISD::STRICT_FTRUNC:
   case ISD::STRICT_FP_ROUND:
   case ISD::STRICT_FP_EXTEND:
-    // These pseudo-ops get legalized as if they were their non-strict
-    // equivalent.  For instance, if ISD::FSQRT is legal then ISD::STRICT_FSQRT
-    // is also legal, but if ISD::FSQRT requires expansion then so does
-    // ISD::STRICT_FSQRT.
-    Action = TLI.getStrictFPOperationAction(Node->getOpcode(),
-                                            Node->getValueType(0));
+    Action = TLI.getOperationAction(Node->getOpcode(), Node->getValueType(0));
+    // If we're asked to expand a strict vector floating-point operation,
+    // by default we're going to simply unroll it.  That is usually the
+    // 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 &&
+        TLI.getStrictFPOperationAction(Node->getOpcode(),
+                                       Node->getValueType(0))
+        == TargetLowering::Legal) {
+      EVT EltVT = Node->getValueType(0).getVectorElementType();
+      if (TLI.getOperationAction(Node->getOpcode(), EltVT)
+          == TargetLowering::Expand &&
+          TLI.getStrictFPOperationAction(Node->getOpcode(), EltVT)
+          == TargetLowering::Legal)
+        Action = TargetLowering::Legal;
+    }
     break;
   case ISD::ADD:
   case ISD::SUB: