Loosen up iv reuse to allow reuse of the same stride but a larger type when truncating from the larger type to smaller type is free.

e.g.
Turns this loop:
LBB1_1: # entry.bb_crit_edge
        xorl    %ecx, %ecx
        xorw    %dx, %dx
        movw    %dx, %si
LBB1_2: # bb
        movl    L_X$non_lazy_ptr, %edi
        movw    %si, (%edi)
        movl    L_Y$non_lazy_ptr, %edi
        movw    %dx, (%edi)
		addw    $4, %dx
		incw    %si
		incl    %ecx
		cmpl    %eax, %ecx
		jne     LBB1_2  # bb
	
into

LBB1_1: # entry.bb_crit_edge
        xorl    %ecx, %ecx
        xorw    %dx, %dx
LBB1_2: # bb
        movl    L_X$non_lazy_ptr, %esi
        movw    %cx, (%esi)
        movl    L_Y$non_lazy_ptr, %esi
        movw    %dx, (%esi)
        addw    $4, %dx
		incl    %ecx
        cmpl    %eax, %ecx
        jne     LBB1_2  # bb


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@43375 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 8 insertions, 1 deletions

diff --git a/include/llvm/Target/TargetLowering.h b/include/llvm/Target/TargetLowering.h
index d55a8af..e092145 100644
--- a/include/llvm/Target/TargetLowering.h
+++ b/include/llvm/Target/TargetLowering.h
@@ -104,7 +104,7 @@ public:
   /// isPow2DivCheap() - Return true if pow2 div is cheaper than a chain of
   /// srl/add/sra.
   bool isPow2DivCheap() const { return Pow2DivIsCheap; }
-  
+
   /// getSetCCResultTy - Return the ValueType of the result of setcc operations.
   ///
   MVT::ValueType getSetCCResultTy() const { return SetCCResultTy; }
@@ -994,6 +994,13 @@ public:
   /// TODO: Handle pre/postinc as well.
   virtual bool isLegalAddressingMode(const AddrMode &AM, const Type *Ty) const;
 
+  /// isTruncateFree - 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 by referencing its sub-register AX.
+  virtual bool isTruncateFree(const Type *Ty1, const Type *Ty2) const {
+    return false;
+  }
+  
   //===--------------------------------------------------------------------===//
   // Div utility functions
   //