Add intrinsics for constrained floating point operations

This commit introduces a set of experimental intrinsics intended to prevent
optimizations that make assumptions about the rounding mode and floating point
exception behavior.  These intrinsics will later be extended to specify
flush-to-zero behavior.  More work is also required to model instruction
dependencies in machine code and to generate these instructions from clang
(when required by pragmas and/or command line options that are not currently
supported).

Differential Revision: https://reviews.llvm.org/D27028

llvm-svn: 293226

1 files changed, 47 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 2e65a2c0297..b654086dd1a 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -5336,6 +5336,13 @@ SelectionDAGBuilder::visitIntrinsicCall(const CallInst &I, unsigned Intrinsic) {
                              getValue(I.getArgOperand(1)),
                              getValue(I.getArgOperand(2))));
     return nullptr;
+  case Intrinsic::experimental_constrained_fadd:
+  case Intrinsic::experimental_constrained_fsub:
+  case Intrinsic::experimental_constrained_fmul:
+  case Intrinsic::experimental_constrained_fdiv:
+  case Intrinsic::experimental_constrained_frem:
+    visitConstrainedFPIntrinsic(I, Intrinsic);
+    return nullptr;
   case Intrinsic::fmuladd: {
     EVT VT = TLI.getValueType(DAG.getDataLayout(), I.getType());
     if (TM.Options.AllowFPOpFusion != FPOpFusion::Strict &&
@@ -5784,6 +5791,46 @@ SelectionDAGBuilder::visitIntrinsicCall(const CallInst &I, unsigned Intrinsic) {
   }
 }
 
+void SelectionDAGBuilder::visitConstrainedFPIntrinsic(const CallInst &I,
+                                                      unsigned Intrinsic) {
+  SDLoc sdl = getCurSDLoc();
+  unsigned Opcode;
+  switch (Intrinsic) {
+  default: llvm_unreachable("Impossible intrinsic");  // Can't reach here.
+  case Intrinsic::experimental_constrained_fadd: 
+    Opcode = ISD::STRICT_FADD;
+    break;
+  case Intrinsic::experimental_constrained_fsub:
+    Opcode = ISD::STRICT_FSUB;
+    break;
+  case Intrinsic::experimental_constrained_fmul:
+    Opcode = ISD::STRICT_FMUL;
+    break;
+  case Intrinsic::experimental_constrained_fdiv:
+    Opcode = ISD::STRICT_FDIV;
+    break;
+  case Intrinsic::experimental_constrained_frem:
+    Opcode = ISD::STRICT_FREM;
+    break;
+  }
+  const TargetLowering &TLI = DAG.getTargetLoweringInfo();
+  SDValue Chain = getRoot();
+  SDValue Ops[3] = { Chain, getValue(I.getArgOperand(0)),
+                     getValue(I.getArgOperand(1)) };
+  SmallVector<EVT, 4> ValueVTs;
+  ComputeValueVTs(TLI, DAG.getDataLayout(), I.getType(), ValueVTs);
+  ValueVTs.push_back(MVT::Other); // Out chain
+
+  SDVTList VTs = DAG.getVTList(ValueVTs);
+  SDValue Result = DAG.getNode(Opcode, sdl, VTs, Ops);
+
+  assert(Result.getNode()->getNumValues() == 2);
+  SDValue OutChain = Result.getValue(1);
+  DAG.setRoot(OutChain);
+  SDValue FPResult = Result.getValue(0);
+  setValue(&I, FPResult);
+}
+
 std::pair<SDValue, SDValue>
 SelectionDAGBuilder::lowerInvokable(TargetLowering::CallLoweringInfo &CLI,
                                     const BasicBlock *EHPadBB) {