Merge from mainline.

Fold x-0 to x in unsafe-fp-math mode. This comes up in the
testcase from PR3376, and in fact is sufficient to completely
avoid the problem in that testcase.

There's an underlying problem though; TLI.isOperationLegal
considers Custom to be Legal, which might be ok in some
cases, but that's what DAGCombiner is using in many places
to test if something is legal when LegalOperations is true.
When DAGCombiner is running after legalize, this isn't
sufficient. I'll address this in a separate commit.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_25@63207 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 16 insertions, 9 deletions

diff --git a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index cb8e69efe4..e3fcc2c216 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -2387,15 +2387,22 @@ SDValue SelectionDAG::getNode(unsigned Opcode, MVT VT,
   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;
+    if (UnsafeFPMath) {
+      if (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;
+      } else if (Opcode == ISD::FSUB) {
+        // 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!");