From 4b30fcb5f51a841d4ef2bb3ed0f29d4754aa9c46 Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Sat, 27 May 2006 01:18:04 +0000
Subject: [PATCH] Refactor some code to expose an interface to constant fold
 and instruction given it's opcode, typeand operands.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@28517 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Utils/Local.cpp | 84 ++++++++++++++++++++--------------
 1 file changed, 49 insertions(+), 35 deletions(-)

diff --git a/lib/Transforms/Utils/Local.cpp b/lib/Transforms/Utils/Local.cpp
index f0da3e554c0..3d1faff0184 100644
--- a/lib/Transforms/Utils/Local.cpp
+++ b/lib/Transforms/Utils/Local.cpp
@@ -64,18 +64,6 @@ Constant *llvm::ConstantFoldInstruction(Instruction *I) {
 
     // If we reach here, all incoming values are the same constant.
     return Result;
-  } else if (CallInst *CI = dyn_cast<CallInst>(I)) {
-    if (Function *F = CI->getCalledFunction())
-      if (canConstantFoldCallTo(F)) {
-        std::vector<Constant*> Args;
-        for (unsigned i = 1, e = CI->getNumOperands(); i != e; ++i)
-          if (Constant *Op = dyn_cast<Constant>(CI->getOperand(i)))
-            Args.push_back(Op);
-          else
-            return 0;
-        return ConstantFoldCall(F, Args);
-      }
-    return 0;
   }
 
   Constant *Op0 = 0, *Op1 = 0;
@@ -91,37 +79,63 @@ Constant *llvm::ConstantFoldInstruction(Instruction *I) {
   case 0: return 0;
   }
 
-  if (isa<BinaryOperator>(I) || isa<ShiftInst>(I))
-    return ConstantExpr::get(I->getOpcode(), Op0, Op1);
+  if (isa<BinaryOperator>(I) || isa<ShiftInst>(I)) {
+    if (Constant *Op0 = dyn_cast<Constant>(I->getOperand(0)))
+      if (Constant *Op1 = dyn_cast<Constant>(I->getOperand(1)))
+        return ConstantExpr::get(I->getOpcode(), Op0, Op1);
+    return 0;  // Operands not constants.
+  }
 
-  switch (I->getOpcode()) {
+  // Scan the operand list, checking to see if the are all constants, if so,
+  // hand off to ConstantFoldInstOperands.
+  std::vector<Constant*> Ops;
+  for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
+    if (Constant *Op = dyn_cast<Constant>(I->getOperand(i)))
+      Ops.push_back(Op);
+    else
+      return 0;  // All operands not constant!
+
+  return ConstantFoldInstOperands(I->getOpcode(), I->getType(), Ops);
+}
+
+/// ConstantFoldInstOperands - Attempt to constant fold an instruction with the
+/// specified opcode and operands.  If successful, the constant result is
+/// returned, if not, null is returned.  Note that this function can fail when
+/// attempting to fold instructions like loads and stores, which have no
+/// constant expression form.
+///
+Constant *llvm::ConstantFoldInstOperands(unsigned Opc, const Type *DestTy,
+                                         const std::vector<Constant*> &Ops) {
+  if (Opc >= Instruction::BinaryOpsBegin && Opc < Instruction::BinaryOpsEnd)
+    return ConstantExpr::get(Opc, Ops[0], Ops[1]);
+  
+  switch (Opc) {
   default: return 0;
+  case Instruction::Call:
+    if (Function *F = dyn_cast<Function>(Ops[0])) {
+      if (canConstantFoldCallTo(F)) {
+        std::vector<Constant*> Args(Ops.begin()+1, Ops.end());
+        return ConstantFoldCall(F, Args);
+      }
+    }
+    return 0;
+  case Instruction::Shl:
+  case Instruction::Shr:
+    return ConstantExpr::get(Opc, Ops[0], Ops[1]);
   case Instruction::Cast:
-    return ConstantExpr::getCast(Op0, I->getType());
+    return ConstantExpr::getCast(Ops[0], DestTy);
   case Instruction::Select:
-    if (Constant *Op2 = dyn_cast<Constant>(I->getOperand(2)))
-      return ConstantExpr::getSelect(Op0, Op1, Op2);
-    return 0;
+    return ConstantExpr::getSelect(Ops[0], Ops[1], Ops[2]);
   case Instruction::ExtractElement:
-    return ConstantExpr::getExtractElement(Op0, Op1);
+    return ConstantExpr::getExtractElement(Ops[0], Ops[1]);
   case Instruction::InsertElement:
-    if (Constant *Op2 = dyn_cast<Constant>(I->getOperand(2)))
-      return ConstantExpr::getInsertElement(Op0, Op1, Op2);
-    return 0;
+    return ConstantExpr::getInsertElement(Ops[0], Ops[1], Ops[2]);
   case Instruction::ShuffleVector:
-    if (Constant *Op2 = dyn_cast<Constant>(I->getOperand(2)))
-      return ConstantExpr::getShuffleVector(Op0, Op1, Op2);
-    return 0;
+    return ConstantExpr::getShuffleVector(Ops[0], Ops[1], Ops[2]);
   case Instruction::GetElementPtr:
-    std::vector<Constant*> IdxList;
-    IdxList.reserve(I->getNumOperands()-1);
-    if (Op1) IdxList.push_back(Op1);
-    for (unsigned i = 2, e = I->getNumOperands(); i != e; ++i)
-      if (Constant *C = dyn_cast<Constant>(I->getOperand(i)))
-        IdxList.push_back(C);
-      else
-        return 0;  // Non-constant operand
-    return ConstantExpr::getGetElementPtr(Op0, IdxList);
+    return ConstantExpr::getGetElementPtr(Ops[0],
+                                          std::vector<Constant*>(Ops.begin()+1, 
+                                                                 Ops.end()));
   }
 }
 
-- 
2.34.1