Move some constant folding logic for loads out of instcombine into

Analysis/ConstantFolding.cpp.  This doesn't change the behavior of
instcombine but makes other clients of ConstantFoldInstruction
able to handle loads.  This was partially extracted from Eli's patch
in PR3152.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@84836 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Analysis/ConstantFolding.h

@@ -62,6 +62,10 @@ Constant *ConstantFoldCompareInstOperands(unsigned Predicate,
                                           LLVMContext &Context,
                                           const TargetData *TD = 0);
 
+/// ConstantFoldLoadFromConstPtr - Return the value that a load from C would
+/// produce if it is constant and determinable.  If this is not determinable,
+/// return null.
+Constant *ConstantFoldLoadFromConstPtr(Constant *C, const TargetData *TD = 0);
 
 /// ConstantFoldLoadThroughGEPConstantExpr - Given a constant and a
 /// getelementptr constantexpr, return the constant value being addressed by the