Fold comparisons against a constant nan, and optimize ORD/UNORD
comparisons with a constant. This allows us to compile isnan to:
_foo:
fcmpu cr7, f1, f1
mfcr r2
rlwinm r3, r2, 0, 31, 31
blr
instead of:
LCPI1_0: ; float
.space 4
_foo:
lis r2, ha16(LCPI1_0)
lfs f0, lo16(LCPI1_0)(r2)
fcmpu cr7, f1, f0
mfcr r2
rlwinm r3, r2, 0, 31, 31
blr
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@45405 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index eb08bba..ad33273 100644
--- a/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -1280,6 +1280,28 @@
// Constant fold or commute setcc.
SDOperand O = DAG.FoldSetCC(VT, N0, N1, Cond);
if (O.Val) return O;
+ } else if (ConstantFPSDNode *CFP = dyn_cast<ConstantFPSDNode>(N1.Val)) {
+ // If the RHS of an FP comparison is a constant, simplify it away in
+ // some cases.
+ if (CFP->getValueAPF().isNaN()) {
+ // If an operand is known to be a nan, we can fold it.
+ switch (ISD::getUnorderedFlavor(Cond)) {
+ default: assert(0 && "Unknown flavor!");
+ case 0: // Known false.
+ return DAG.getConstant(0, VT);
+ case 1: // Known true.
+ return DAG.getConstant(1, VT);
+ case 2: // undefind.
+ return DAG.getNode(ISD::UNDEF, VT);
+ }
+ }
+
+ // Otherwise, we know the RHS is not a NaN. Simplify the node to drop the
+ // constant if knowing that the operand is non-nan is enough. We prefer to
+ // have SETO(x,x) instead of SETO(x, 0.0) because this avoids having to
+ // materialize 0.0.
+ if (Cond == ISD::SETO || Cond == ISD::SETUO)
+ return DAG.getSetCC(VT, N0, N0, Cond);
}
if (N0 == N1) {