From d261dc650a01ac5c51ab10f97f1e35aa6a770721 Mon Sep 17 00:00:00 2001
From: Duncan Sands <baldrick@free.fr>
Date: Wed, 17 Nov 2010 08:35:29 +0000
Subject: [PATCH] Previously SimplifyInstruction could report that an
 instruction simplified to itself (this can only happen in unreachable
 blocks). Change it to return null instead.  Hopefully this will fix some
 buildbot failures.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@119490 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/Analysis/InstructionSimplify.h |  2 -
 lib/Analysis/InstructionSimplify.cpp        | 46 ++++++++++++++-------
 lib/Analysis/Lint.cpp                       |  3 +-
 3 files changed, 32 insertions(+), 19 deletions(-)

diff --git a/include/llvm/Analysis/InstructionSimplify.h b/include/llvm/Analysis/InstructionSimplify.h
index b59adc1de9b..965e71be411 100644
--- a/include/llvm/Analysis/InstructionSimplify.h
+++ b/include/llvm/Analysis/InstructionSimplify.h
@@ -75,8 +75,6 @@ namespace llvm {
 
   /// SimplifyInstruction - See if we can compute a simplified version of this
   /// instruction.  If not, this returns null.
-  /// WARNING: If called on unreachable code, an instruction may be reported
-  /// to simplify to itself.
   Value *SimplifyInstruction(Instruction *I, const TargetData *TD = 0,
                              const DominatorTree *DT = 0);
 
diff --git a/lib/Analysis/InstructionSimplify.cpp b/lib/Analysis/InstructionSimplify.cpp
index c540d6fd2c0..5ad842b38f1 100644
--- a/lib/Analysis/InstructionSimplify.cpp
+++ b/lib/Analysis/InstructionSimplify.cpp
@@ -756,34 +756,50 @@ Value *llvm::SimplifyCmpInst(unsigned Predicate, Value *LHS, Value *RHS,
 /// instruction.  If not, this returns null.
 Value *llvm::SimplifyInstruction(Instruction *I, const TargetData *TD,
                                  const DominatorTree *DT) {
+  Value *Result;
+
   switch (I->getOpcode()) {
   default:
-    return ConstantFoldInstruction(I, TD);
+    Result = ConstantFoldInstruction(I, TD);
+    break;
   case Instruction::Add:
-    return SimplifyAddInst(I->getOperand(0), I->getOperand(1),
-                           cast<BinaryOperator>(I)->hasNoSignedWrap(),
-                           cast<BinaryOperator>(I)->hasNoUnsignedWrap(),
-                           TD, DT);
+    Result = SimplifyAddInst(I->getOperand(0), I->getOperand(1),
+                             cast<BinaryOperator>(I)->hasNoSignedWrap(),
+                             cast<BinaryOperator>(I)->hasNoUnsignedWrap(),
+                             TD, DT);
+    break;
   case Instruction::And:
-    return SimplifyAndInst(I->getOperand(0), I->getOperand(1), TD, DT);
+    Result = SimplifyAndInst(I->getOperand(0), I->getOperand(1), TD, DT);
+    break;
   case Instruction::Or:
-    return SimplifyOrInst(I->getOperand(0), I->getOperand(1), TD, DT);
+    Result = SimplifyOrInst(I->getOperand(0), I->getOperand(1), TD, DT);
+    break;
   case Instruction::ICmp:
-    return SimplifyICmpInst(cast<ICmpInst>(I)->getPredicate(),
-                            I->getOperand(0), I->getOperand(1), TD, DT);
+    Result = SimplifyICmpInst(cast<ICmpInst>(I)->getPredicate(),
+                              I->getOperand(0), I->getOperand(1), TD, DT);
+    break;
   case Instruction::FCmp:
-    return SimplifyFCmpInst(cast<FCmpInst>(I)->getPredicate(),
-                            I->getOperand(0), I->getOperand(1), TD, DT);
+    Result = SimplifyFCmpInst(cast<FCmpInst>(I)->getPredicate(),
+                              I->getOperand(0), I->getOperand(1), TD, DT);
+    break;
   case Instruction::Select:
-    return SimplifySelectInst(I->getOperand(0), I->getOperand(1),
-                              I->getOperand(2), TD, DT);
+    Result = SimplifySelectInst(I->getOperand(0), I->getOperand(1),
+                                I->getOperand(2), TD, DT);
+    break;
   case Instruction::GetElementPtr: {
     SmallVector<Value*, 8> Ops(I->op_begin(), I->op_end());
-    return SimplifyGEPInst(&Ops[0], Ops.size(), TD, DT);
+    Result = SimplifyGEPInst(&Ops[0], Ops.size(), TD, DT);
+    break;
   }
   case Instruction::PHI:
-    return SimplifyPHINode(cast<PHINode>(I), DT);
+    Result = SimplifyPHINode(cast<PHINode>(I), DT);
+    break;
   }
+
+  /// If called on unreachable code, the above logic may report that the
+  /// instruction simplified to itself.  Make life easier for users by
+  /// detecting that case here, returning null if it occurs.
+  return Result == I ? 0 : Result;
 }
 
 /// ReplaceAndSimplifyAllUses - Perform From->replaceAllUsesWith(To) and then
diff --git a/lib/Analysis/Lint.cpp b/lib/Analysis/Lint.cpp
index 8b76b873374..e5e7cd38576 100644
--- a/lib/Analysis/Lint.cpp
+++ b/lib/Analysis/Lint.cpp
@@ -616,8 +616,7 @@ Value *Lint::findValueImpl(Value *V, bool OffsetOk,
   // As a last resort, try SimplifyInstruction or constant folding.
   if (Instruction *Inst = dyn_cast<Instruction>(V)) {
     if (Value *W = SimplifyInstruction(Inst, TD, DT))
-      if (W != Inst)
-        return findValueImpl(W, OffsetOk, Visited);
+      return findValueImpl(W, OffsetOk, Visited);
   } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
     if (Value *W = ConstantFoldConstantExpression(CE, TD))
       if (W != V)