[llvm-commits] [llvm] r62860 - in /llvm/trunk/lib/CodeGen/SelectionDAG: DAGCombiner.cpp SelectionDAG.cpp

[Dan Gohman]

Author: djg
Date: Fri Jan 23 13:10:37 2009
New Revision: 62860

URL: http://llvm.org/viewvc/llvm-project?rev=62860&view=rev
Log:
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.

Modified:
    llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
    llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

Modified: llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp?rev=62860&r1=62859&r2=62860&view=diff

==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp Fri Jan 23 13:10:37 2009
@@ -3853,6 +3853,9 @@
   // fold (fsub c1, c2) -> c1-c2
   if (N0CFP && N1CFP && VT != MVT::ppcf128)
     return DAG.getNode(ISD::FSUB, VT, N0, N1);
+  // fold (A-0) -> A
+  if (UnsafeFPMath && N1CFP && N1CFP->getValueAPF().isZero())
+    return N0;
   // fold (0-B) -> -B
   if (UnsafeFPMath && N0CFP && N0CFP->getValueAPF().isZero()) {
     if (isNegatibleForFree(N1, LegalOperations))

Modified: llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp?rev=62860&r1=62859&r2=62860&view=diff

==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp Fri Jan 23 13:10:37 2009
@@ -2402,15 +2402,22 @@
   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!");