Don't create ISD::FNEG nodes after legalize if they aren't legal.

Simplify x+0 to x in unsafe-fp-math mode. This avoids a bunch of
redundant work in many cases, because in unsafe-fp-math mode,
ISD::FADD with a constant is considered free to negate, so the
DAGCombiner often negates x+0 to -0-x thinking it's free, when
in reality the end result is -x, which is more expensive than x.

Also, combine x*0 to 0.

This fixes PR3374.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@62789 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 30 insertions, 8 deletions

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index f7c1d06..e494da3 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -3814,6 +3814,9 @@ SDValue DAGCombiner::visitFADD(SDNode *N) {
   // canonicalize constant to RHS
   if (N0CFP && !N1CFP)
     return DAG.getNode(ISD::FADD, VT, N1, N0);
+  // fold (A + 0) -> A
+  if (UnsafeFPMath && N1CFP && N1CFP->getValueAPF().isZero())
+    return N0;
   // fold (A + (-B)) -> A-B
   if (isNegatibleForFree(N1, LegalOperations) == 2)
     return DAG.getNode(ISD::FSUB, VT, N0, 
@@ -3852,7 +3855,8 @@ SDValue DAGCombiner::visitFSUB(SDNode *N) {
   if (UnsafeFPMath && N0CFP && N0CFP->getValueAPF().isZero()) {
     if (isNegatibleForFree(N1, LegalOperations))
       return GetNegatedExpression(N1, DAG, LegalOperations);
-    return DAG.getNode(ISD::FNEG, VT, N1);
+    if (!LegalOperations || TLI.isOperationLegal(ISD::FNEG, VT))
+      return DAG.getNode(ISD::FNEG, VT, N1);
   }
   // fold (A-(-B)) -> A+B
   if (isNegatibleForFree(N1, LegalOperations))
@@ -3881,12 +3885,16 @@ SDValue DAGCombiner::visitFMUL(SDNode *N) {
   // canonicalize constant to RHS
   if (N0CFP && !N1CFP)
     return DAG.getNode(ISD::FMUL, VT, N1, N0);
+  // fold (A * 0) -> 0
+  if (UnsafeFPMath && N1CFP && N1CFP->getValueAPF().isZero())
+    return N1;
   // fold (fmul X, 2.0) -> (fadd X, X)
   if (N1CFP && N1CFP->isExactlyValue(+2.0))
     return DAG.getNode(ISD::FADD, VT, N0, N0);
   // fold (fmul X, -1.0) -> (fneg X)
   if (N1CFP && N1CFP->isExactlyValue(-1.0))
-    return DAG.getNode(ISD::FNEG, VT, N0);
+    if (!LegalOperations || TLI.isOperationLegal(ISD::FNEG, VT))
+      return DAG.getNode(ISD::FNEG, VT, N0);
   
   // -X * -Y -> X*Y
   if (char LHSNeg = isNegatibleForFree(N0, LegalOperations)) {
@@ -3970,10 +3978,13 @@ SDValue DAGCombiner::visitFCOPYSIGN(SDNode *N) {
     const APFloat& V = N1CFP->getValueAPF();
     // copysign(x, c1) -> fabs(x)       iff ispos(c1)
     // copysign(x, c1) -> fneg(fabs(x)) iff isneg(c1)
-    if (!V.isNegative())
-      return DAG.getNode(ISD::FABS, VT, N0);
-    else
-      return DAG.getNode(ISD::FNEG, VT, DAG.getNode(ISD::FABS, VT, N0));
+    if (!V.isNegative()) {
+      if (!LegalOperations || TLI.isOperationLegal(ISD::FABS, VT))
+        return DAG.getNode(ISD::FABS, VT, N0);
+    } else {
+      if (!LegalOperations || TLI.isOperationLegal(ISD::FNEG, VT))
+        return DAG.getNode(ISD::FNEG, VT, DAG.getNode(ISD::FABS, VT, N0));
+    }
   }
   
   // copysign(fabs(x), y) -> copysign(x, y)
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index a088560..2974486 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -27,6 +27,7 @@
 #include "llvm/Target/TargetRegisterInfo.h"
 #include "llvm/Target/TargetData.h"
 #include "llvm/Target/TargetLowering.h"
+#include "llvm/Target/TargetOptions.h"
 #include "llvm/Target/TargetInstrInfo.h"
 #include "llvm/Target/TargetMachine.h"
 #include "llvm/Support/CommandLine.h"
@@ -2391,16 +2392,26 @@ SDValue SelectionDAG::getNode(unsigned Opcode, MVT VT,
   case ISD::UREM:
   case ISD::MULHU:
   case ISD::MULHS:
-    assert(VT.isInteger() && "This operator does not apply to FP types!");
-    // fall through
   case ISD::MUL:
   case ISD::SDIV:
   case ISD::SREM:
+    assert(VT.isInteger() && "This operator does not apply to FP types!");
+    // fall through
   case ISD::FADD:
   case ISD::FSUB:
   case ISD::FMUL:
   case ISD::FDIV:
   case ISD::FREM:
+    if (UnsafeFPMath && Opcode == ISD::FADD) {
+      // 0+x --> x
+      if (ConstantFPSDNode *CFP = dyn_cast<ConstantFPSDNode>(N1))
+        if (CFP->getValueAPF().isZero())
+          return N2;
+      // x+0 --> x
+      if (ConstantFPSDNode *CFP = dyn_cast<ConstantFPSDNode>(N2))
+        if (CFP->getValueAPF().isZero())
+          return N1;
+    }
     assert(N1.getValueType() == N2.getValueType() &&
            N1.getValueType() == VT && "Binary operator types must match!");
     break;