stub out a new libanalysis "instruction simplify" interface that

takes decimated instructions and applies identities to them.  This
is pretty minimal at this point, but I plan to pull some instcombine
logic out into these and similar routines.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@86613 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Analysis/InstructionSimplify.h

@@ -0,0 +1,37 @@
+//===-- InstructionSimplify.h - Fold instructions into simpler forms ------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file declares routines for folding instructions into simpler forms that
+// do not require creating new instructions.  For example, this does constant
+// folding, and can handle identities like (X&0)->0.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ANALYSIS_INSTRUCTIONSIMPLIFY_H
+#define LLVM_ANALYSIS_INSTRUCTIONSIMPLIFY_H
+
+namespace llvm {
+  class Value;
+  class TargetData;
+  
+  /// SimplifyCompare - Given operands for a CmpInst, see if we can
+  /// fold the result.  If not, this returns null.
+  Value *SimplifyCompare(unsigned Predicate, Value *LHS, Value *RHS,
+                         const TargetData *TD = 0);
+  
+  
+  /// SimplifyBinOp - Given operands for a BinaryOperator, see if we can
+  /// fold the result.  If not, this returns null.
+  Value *SimplifyBinOp(unsigned Opcode, Value *LHS, Value *RHS, 
+                       const TargetData *TD = 0);
+  
+} // end namespace llvm
+
+#endif
+

lib/Analysis/CMakeLists.txt

@@ -15,6 +15,7 @@ add_llvm_library(LLVMAnalysis
   IVUsers.cpp
   InlineCost.cpp
   InstCount.cpp
+  InstructionSimplify.cpp
   Interval.cpp
   IntervalPartition.cpp
   LibCallAliasAnalysis.cpp

lib/Analysis/InstructionSimplify.cpp

@@ -0,0 +1,57 @@
+//===- InstructionSimplify.cpp - Fold instruction operands ----------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements routines for folding instructions into simpler forms
+// that do not require creating new instructions.  For example, this does
+// constant folding, and can handle identities like (X&0)->0.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Analysis/InstructionSimplify.h"
+#include "llvm/Analysis/ConstantFolding.h"
+#include "llvm/Instructions.h"
+using namespace llvm;
+
+
+/// SimplifyBinOp - Given operands for a BinaryOperator, see if we can
+/// fold the result.  If not, this returns null.
+Value *llvm::SimplifyBinOp(unsigned Opcode, Value *LHS, Value *RHS, 
+                           const TargetData *TD) {
+  if (Constant *CLHS = dyn_cast<Constant>(LHS))
+    if (Constant *CRHS = dyn_cast<Constant>(RHS)) {
+      Constant *COps[] = {CLHS, CRHS};
+      return ConstantFoldInstOperands(Opcode, LHS->getType(), COps, 2, TD);
+    }     
+  return 0;
+}
+
+
+/// SimplifyCompare - Given operands for a CmpInst, see if we can
+/// fold the result.
+Value *llvm::SimplifyCompare(unsigned Predicate, Value *LHS, Value *RHS,
+                             const TargetData *TD) {
+  CmpInst::Predicate Pred = (CmpInst::Predicate)Predicate;
+  
+  if (Constant *CLHS = dyn_cast<Constant>(LHS))
+    if (Constant *CRHS = dyn_cast<Constant>(RHS)) {
+      Constant *COps[] = {CLHS, CRHS};
+      return ConstantFoldCompareInstOperands(Pred, COps, 2, TD);
+    }
+  
+  // If this is an integer compare and the LHS and RHS are the same, fold it.
+  if (LHS == RHS)
+    if (isa<IntegerType>(LHS->getType()) || isa<PointerType>(LHS->getType())) {
+      if (ICmpInst::isTrueWhenEqual(Pred))
+        return ConstantInt::getTrue(LHS->getContext());
+      else
+        return ConstantInt::getFalse(LHS->getContext());
+    }
+  return 0;
+}
+