Implement add.ll:test22, a common case in MSIL files

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@14587 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 18 insertions, 0 deletions

diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index bf57119486..c0d0591c9b 100644
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -122,6 +122,7 @@ namespace {
     Instruction *visitFreeInst(FreeInst &FI);
     Instruction *visitLoadInst(LoadInst &LI);
     Instruction *visitBranchInst(BranchInst &BI);
+    Instruction *visitSwitchInst(SwitchInst &SI);
 
     // visitInstruction - Specify what to return for unhandled instructions...
     Instruction *visitInstruction(Instruction &I) { return 0; }
@@ -3004,6 +3005,23 @@ Instruction *InstCombiner::visitBranchInst(BranchInst &BI) {
   return 0;
 }
 
+Instruction *InstCombiner::visitSwitchInst(SwitchInst &SI) {
+  Value *Cond = SI.getCondition();
+  if (Instruction *I = dyn_cast<Instruction>(Cond)) {
+    if (I->getOpcode() == Instruction::Add)
+      if (ConstantInt *AddRHS = dyn_cast<ConstantInt>(I->getOperand(1))) {
+        // change 'switch (X+4) case 1:' into 'switch (X) case -3'
+        for (unsigned i = 2, e = SI.getNumOperands(); i != e; i += 2)
+          SI.setOperand(i, ConstantExpr::getSub(cast<Constant>(SI.getOperand(i)),
+                                                AddRHS));
+        SI.setOperand(0, I->getOperand(0));
+        WorkList.push_back(I);
+        return &SI;
+      }
+  }
+  return 0;
+}
+
 
 void InstCombiner::removeFromWorkList(Instruction *I) {
   WorkList.erase(std::remove(WorkList.begin(), WorkList.end(), I),