From c514c1f5218b8fe7499a0b9a4737860344cf4c43 Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Fri, 27 Nov 2009 00:29:05 +0000
Subject: [PATCH] factor some instcombine simplifications for getelementptr out
 to a new SimplifyGEPInst method in InstructionSimplify.h.  No functionality
 change.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@89980 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/Analysis/InstructionSimplify.h   |  5 +++
 lib/Analysis/InstructionSimplify.cpp          | 32 +++++++++++++++++++
 .../Scalar/InstructionCombining.cpp           | 19 ++++++-----
 3 files changed, 46 insertions(+), 10 deletions(-)

diff --git a/include/llvm/Analysis/InstructionSimplify.h b/include/llvm/Analysis/InstructionSimplify.h
index aa5c0f554bc..1cd7e565563 100644
--- a/include/llvm/Analysis/InstructionSimplify.h
+++ b/include/llvm/Analysis/InstructionSimplify.h
@@ -42,6 +42,11 @@ namespace llvm {
                           const TargetData *TD = 0);
   
 
+  /// SimplifyGEPInst - Given operands for an GetElementPtrInst, see if we can
+  /// fold the result.  If not, this returns null.
+  Value *SimplifyGEPInst(Value * const *Ops, unsigned NumOps,
+                         const TargetData *TD = 0);
+  
   //=== Helper functions for higher up the class hierarchy.
   
   
diff --git a/lib/Analysis/InstructionSimplify.cpp b/lib/Analysis/InstructionSimplify.cpp
index f9953e3c98b..7a7eb6b6829 100644
--- a/lib/Analysis/InstructionSimplify.cpp
+++ b/lib/Analysis/InstructionSimplify.cpp
@@ -264,6 +264,34 @@ Value *llvm::SimplifyFCmpInst(unsigned Predicate, Value *LHS, Value *RHS,
   return 0;
 }
 
+/// SimplifyGEPInst - Given operands for an GetElementPtrInst, see if we can
+/// fold the result.  If not, this returns null.
+Value *llvm::SimplifyGEPInst(Value *const *Ops, unsigned NumOps,
+                             const TargetData *TD) {
+  // getelementptr P -> P.
+  if (NumOps == 1)
+    return Ops[0];
+
+  // TODO.
+  //if (isa<UndefValue>(Ops[0]))
+  //  return UndefValue::get(GEP.getType());
+
+  // getelementptr P, 0 -> P.
+  if (NumOps == 2)
+    if (ConstantInt *C = dyn_cast<ConstantInt>(Ops[1]))
+      if (C->isZero())
+        return Ops[0];
+  
+  // Check to see if this is constant foldable.
+  for (unsigned i = 0; i != NumOps; ++i)
+    if (!isa<Constant>(Ops[i]))
+      return 0;
+  
+  return ConstantExpr::getGetElementPtr(cast<Constant>(Ops[0]),
+                                        (Constant *const*)Ops+1, NumOps-1);
+}
+
+
 //=== Helper functions for higher up the class hierarchy.
 
 /// SimplifyBinOp - Given operands for a BinaryOperator, see if we can
@@ -309,6 +337,10 @@ Value *llvm::SimplifyInstruction(Instruction *I, const TargetData *TD) {
   case Instruction::FCmp:
     return SimplifyFCmpInst(cast<FCmpInst>(I)->getPredicate(),
                             I->getOperand(0), I->getOperand(1), TD);
+  case Instruction::GetElementPtr: {
+    SmallVector<Value*, 8> Ops(I->op_begin(), I->op_end());
+    return SimplifyGEPInst(&Ops[0], Ops.size(), TD);
+  }
   }
 }
 
diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index c7ab9df5722..95563b0493b 100644
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -11429,21 +11429,16 @@ Instruction *InstCombiner::visitPHINode(PHINode &PN) {
 }
 
 Instruction *InstCombiner::visitGetElementPtrInst(GetElementPtrInst &GEP) {
+  SmallVector<Value*, 8> Ops(GEP.op_begin(), GEP.op_end());
+
+  if (Value *V = SimplifyGEPInst(&Ops[0], Ops.size(), TD))
+    return ReplaceInstUsesWith(GEP, V);
+
   Value *PtrOp = GEP.getOperand(0);
-  // Eliminate 'getelementptr %P, i32 0' and 'getelementptr %P', they are noops.
-  if (GEP.getNumOperands() == 1)
-    return ReplaceInstUsesWith(GEP, PtrOp);
 
   if (isa<UndefValue>(GEP.getOperand(0)))
     return ReplaceInstUsesWith(GEP, UndefValue::get(GEP.getType()));
 
-  bool HasZeroPointerIndex = false;
-  if (Constant *C = dyn_cast<Constant>(GEP.getOperand(1)))
-    HasZeroPointerIndex = C->isNullValue();
-
-  if (GEP.getNumOperands() == 2 && HasZeroPointerIndex)
-    return ReplaceInstUsesWith(GEP, PtrOp);
-
   // Eliminate unneeded casts for indices.
   if (TD) {
     bool MadeChange = false;
@@ -11548,6 +11543,10 @@ Instruction *InstCombiner::visitGetElementPtrInst(GetElementPtrInst &GEP) {
       return 0;
     }
     
+    bool HasZeroPointerIndex = false;
+    if (ConstantInt *C = dyn_cast<ConstantInt>(GEP.getOperand(1)))
+      HasZeroPointerIndex = C->isZero();
+    
     // Transform: GEP (bitcast [10 x i8]* X to [0 x i8]*), i32 0, ...
     // into     : GEP [10 x i8]* X, i32 0, ...
     //