[PATCH] D8304: Fix backward operands in call to isTruncateFree() and improve comments.

[Steve King]

srking retitled this revision from "Fix backward operands in call to isTruncateFree() and add asserts." to "Fix backward operands in call to isTruncateFree() and improve comments.".
srking updated the summary for this revision.
srking updated this revision to Diff 30840.
srking added a comment.

Tried to address review comments from Jonathan Roelofs.  NFC from previous patch.  Updated patch title text and summary to remove statement about asserts.


http://reviews.llvm.org/D8304

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

Index: lib/CodeGen/SelectionDAG/DAGCombiner.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -9719,8 +9719,8 @@
     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()))
+      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)
Index: include/llvm/Target/TargetLowering.h
===================================================================
--- include/llvm/Target/TargetLowering.h
+++ include/llvm/Target/TargetLowering.h
@@ -1504,23 +1504,24 @@
     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 <= ToTy.
+  virtual bool isTruncateFree(Type *FromTy, Type *ToTy) const {
     return false;
   }
 
-  /// Return true if a truncation from Ty1 to Ty2 is permitted when deciding
+  /// Return true if a truncation from FromTy to ToTy is permitted when deciding
   /// whether a call is in tail position. Typically this means that both results
   /// would be assigned to the same register or stack slot, but it could mean
   /// the target performs adequate checks of its own before proceeding with the
-  /// tail call.
-  virtual bool allowTruncateForTailCall(Type * /*Ty1*/, Type * /*Ty2*/) const {
+  /// tail call.  Targets must return false when FromTy <= ToTy.
+  virtual bool allowTruncateForTailCall(Type *FromTy, Type *ToTy) const {
     return false;
   }
 
-  virtual bool isTruncateFree(EVT /*VT1*/, EVT /*VT2*/) const {
+  virtual bool isTruncateFree(EVT FromVT, EVT ToVT) const {
     return false;
   }
 
@@ -1561,11 +1562,12 @@
   /// isTruncateFree(Ty2, Ty1) is true, this does not necessarily apply to
   /// truncate instructions. e.g. on x86-64, all instructions that define 32-bit
   /// values implicit zero-extend the result out to 64 bits.
-  virtual bool isZExtFree(Type * /*Ty1*/, Type * /*Ty2*/) const {
+  /// Targets must return false when FromTy >= ToTy.
+  virtual bool isZExtFree(Type *FromTy, Type *ToTy) const {
     return false;
   }
 
-  virtual bool isZExtFree(EVT /*VT1*/, EVT /*VT2*/) const {
+  virtual bool isZExtFree(EVT FromTy, EVT ToTy) const {
     return false;
   }
 


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