Add a roundToIntegral method to APFloat, which can be parameterized over various rounding modes. Use this to implement SelectionDAG constant folding of FFLOOR, FCEIL, and FTRUNC.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@161807 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/ADT/APFloat.h

@@ -274,6 +274,7 @@ namespace llvm {
     /* C fmod, or llvm frem. */
     opStatus mod(const APFloat &, roundingMode);
     opStatus fusedMultiplyAdd(const APFloat &, const APFloat &, roundingMode);
+    opStatus roundToIntegral(roundingMode);
 
     /* Sign operations.  */
     void changeSign();

lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -228,6 +228,9 @@ namespace {
     SDValue visitFP_EXTEND(SDNode *N);
     SDValue visitFNEG(SDNode *N);
     SDValue visitFABS(SDNode *N);
+    SDValue visitFCEIL(SDNode *N);
+    SDValue visitFTRUNC(SDNode *N);
+    SDValue visitFFLOOR(SDNode *N);
     SDValue visitBRCOND(SDNode *N);
     SDValue visitBR_CC(SDNode *N);
     SDValue visitLOAD(SDNode *N);
@@ -1140,6 +1143,9 @@ SDValue DAGCombiner::visit(SDNode *N) {
   case ISD::FP_EXTEND:          return visitFP_EXTEND(N);
   case ISD::FNEG:               return visitFNEG(N);
   case ISD::FABS:               return visitFABS(N);
+  case ISD::FFLOOR:             return visitFFLOOR(N);
+  case ISD::FCEIL:              return visitFCEIL(N);
+  case ISD::FTRUNC:             return visitFTRUNC(N);
   case ISD::BRCOND:             return visitBRCOND(N);
   case ISD::BR_CC:              return visitBR_CC(N);
   case ISD::LOAD:               return visitLOAD(N);
@@ -6243,6 +6249,42 @@ SDValue DAGCombiner::visitFNEG(SDNode *N) {
   return SDValue();
 }
 
+SDValue DAGCombiner::visitFCEIL(SDNode *N) {
+  SDValue N0 = N->getOperand(0);
+  ConstantFPSDNode *N0CFP = dyn_cast<ConstantFPSDNode>(N0);
+  EVT VT = N->getValueType(0);
+
+  // fold (fceil c1) -> fceil(c1)
+  if (N0CFP && VT != MVT::ppcf128)
+    return DAG.getNode(ISD::FCEIL, N->getDebugLoc(), VT, N0);
+
+  return SDValue();
+}
+
+SDValue DAGCombiner::visitFTRUNC(SDNode *N) {
+  SDValue N0 = N->getOperand(0);
+  ConstantFPSDNode *N0CFP = dyn_cast<ConstantFPSDNode>(N0);
+  EVT VT = N->getValueType(0);
+
+  // fold (ftrunc c1) -> ftrunc(c1)
+  if (N0CFP && VT != MVT::ppcf128)
+    return DAG.getNode(ISD::FTRUNC, N->getDebugLoc(), VT, N0);
+
+  return SDValue();
+}
+
+SDValue DAGCombiner::visitFFLOOR(SDNode *N) {
+  SDValue N0 = N->getOperand(0);
+  ConstantFPSDNode *N0CFP = dyn_cast<ConstantFPSDNode>(N0);
+  EVT VT = N->getValueType(0);
+
+  // fold (ffloor c1) -> ffloor(c1)
+  if (N0CFP && VT != MVT::ppcf128)
+    return DAG.getNode(ISD::FFLOOR, N->getDebugLoc(), VT, N0);
+
+  return SDValue();
+}
+
 SDValue DAGCombiner::visitFABS(SDNode *N) {
   SDValue N0 = N->getOperand(0);
   ConstantFPSDNode *N0CFP = dyn_cast<ConstantFPSDNode>(N0);

lib/CodeGen/SelectionDAG/SelectionDAG.cpp

@@ -2483,6 +2483,24 @@ SDValue SelectionDAG::getNode(unsigned Opcode, DebugLoc DL,
       case ISD::FABS:
         V.clearSign();
         return getConstantFP(V, VT);
+      case ISD::FCEIL: {
+        APFloat::opStatus fs = V.roundToIntegral(APFloat::rmTowardPositive);
+        if (fs == APFloat::opOK || fs == APFloat::opInexact)
+          return getConstantFP(V, VT);
+        break;
+      }
+      case ISD::FTRUNC: {
+        APFloat::opStatus fs = V.roundToIntegral(APFloat::rmTowardZero);
+        if (fs == APFloat::opOK || fs == APFloat::opInexact)
+          return getConstantFP(V, VT);
+        break;
+      }
+      case ISD::FFLOOR: {
+        APFloat::opStatus fs = V.roundToIntegral(APFloat::rmTowardNegative);
+        if (fs == APFloat::opOK || fs == APFloat::opInexact)
+          return getConstantFP(V, VT);
+        break;
+      }
       case ISD::FP_EXTEND: {
         bool ignored;
         // This can return overflow, underflow, or inexact; we don't care.

lib/Support/APFloat.cpp

@@ -1765,6 +1765,32 @@ APFloat::fusedMultiplyAdd(const APFloat &multiplicand,
   return fs;
 }
 
+/* Rounding-mode corrrect round to integral value.  */
+APFloat::opStatus APFloat::roundToIntegral(roundingMode rounding_mode) {
+  opStatus fs;
+  assertArithmeticOK(*semantics);
+
+  // The algorithm here is quite simple: we add 2^(p-1), where p is the
+  // precision of our format, and then subtract it back off again.  The choice
+  // of rounding modes for the addition/subtraction determines the rounding mode
+  // for our integral rounding as well.
+  APInt IntegerConstant(NextPowerOf2(semanticsPrecision(*semantics)),
+                        1 << (semanticsPrecision(*semantics)-1));
+  APFloat MagicConstant(*semantics);
+  fs = MagicConstant.convertFromAPInt(IntegerConstant, false,
+                                      rmNearestTiesToEven);
+  if (fs != opOK)
+    return fs;
+
+  fs = add(MagicConstant, rounding_mode);
+  if (fs != opOK && fs != opInexact)
+    return fs;
+
+  fs = subtract(MagicConstant, rounding_mode);
+  return fs;
+}
+
+
 /* Comparison requires normalized numbers.  */
 APFloat::cmpResult
 APFloat::compare(const APFloat &rhs) const

test/CodeGen/ARM/floorf.ll

@@ -0,0 +1,29 @@
+; RUN: llc -march=arm < %s | FileCheck %s
+
+; CHECK: test1
+define float @test1() nounwind uwtable readnone ssp {
+; CHECK-NOT: floorf
+  %foo = call float @floorf(float 0x4000CCCCC0000000) nounwind readnone
+  ret float %foo
+}
+
+; CHECK: test2
+define float @test2() nounwind uwtable readnone ssp {
+; CHECK-NOT: ceilf
+  %foo = call float @ceilf(float 0x4000CCCCC0000000) nounwind readnone
+  ret float %foo
+}
+
+; CHECK: test3
+define float @test3() nounwind uwtable readnone ssp {
+; CHECK-NOT: truncf
+  %foo = call float @truncf(float 0x4000CCCCC0000000) nounwind readnone
+  ret float %foo
+}
+
+declare float @floorf(float) nounwind readnone
+declare float @ceilf(float) nounwind readnone
+declare float @truncf(float) nounwind readnone
+
+
+