[PATCH] Fix backward operands in call to isTruncateFree() and add asserts.

[Steve King]

Removed the assert() due to cases that call isTruncateFree without regard to type size.  Improved comment for these odd cases.
Verified regression checks pass.


http://reviews.llvm.org/D8304

Files:
  include/llvm/Target/TargetLowering.h
  lib/CodeGen/SelectionDAG/DAGCombiner.cpp

Index: include/llvm/Target/TargetLowering.h
===================================================================
--- include/llvm/Target/TargetLowering.h
+++ include/llvm/Target/TargetLowering.h
@@ -1462,10 +1462,15 @@
     return false;
   }
 
-  /// Return true if it's free to truncate a value of type Ty1 to type
-  /// Ty2. e.g. On x86 it's free to truncate a i32 value in register EAX to i16
+  /// Return true if it's free to truncate a value of type FromTy to type
+  /// ToTy. e.g. On x86 it's free to truncate a i32 value in register EAX to i16
   /// by referencing its sub-register AX.
-  virtual bool isTruncateFree(Type * /*Ty1*/, Type * /*Ty2*/) const {
+  /// Targets must return false when FromTy is smaller or equal than ToTy.
+  virtual bool isTruncateFree(Type *FromTy, Type *ToTy) const {
+    return false;
+  }
+
+  virtual bool isTruncateFree(EVT FromVT, EVT ToVT) const {
     return false;
   }
 
@@ -1478,10 +1483,6 @@
     return false;
   }
 
-  virtual bool isTruncateFree(EVT /*VT1*/, EVT /*VT2*/) const {
-    return false;
-  }
-
   virtual bool isProfitableToHoist(Instruction *I) const { return true; }
 
   /// Return true if the extension represented by \p I is free.
Index: lib/CodeGen/SelectionDAG/DAGCombiner.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -9149,8 +9149,9 @@
     void addSliceGain(const LoadedSlice &LS) {
       // Each slice saves a truncate.
       const TargetLowering &TLI = LS.DAG->getTargetLoweringInfo();
-      if (!TLI.isTruncateFree(LS.Inst->getValueType(0),
-                              LS.Inst->getOperand(0).getValueType()))
+      // isTruncateFree(FromType,ToType)
+      if (!TLI.isTruncateFree(LS.Inst->getOperand(0).getValueType(),
+                                            LS.Inst->getValueType(0)))
         ++Truncates;
       // If there is a shift amount, this slice gets rid of it.
       if (LS.Shift)

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