From 3d69f46d64ca4cb8062b27c94b3077fa9048ebf8 Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Fri, 12 Mar 2004 05:52:32 +0000
Subject: [PATCH] Add trivial optimizations for select instructions

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@12317 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Scalar/InstructionCombining.cpp | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index 724243369b5..7d308be1f21 100644
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -108,6 +108,7 @@ namespace {
     Instruction *visitSetCondInst(BinaryOperator &I);
     Instruction *visitShiftInst(ShiftInst &I);
     Instruction *visitCastInst(CastInst &CI);
+    Instruction *visitSelectInst(SelectInst &CI);
     Instruction *visitCallInst(CallInst &CI);
     Instruction *visitInvokeInst(InvokeInst &II);
     Instruction *visitPHINode(PHINode &PN);
@@ -1931,6 +1932,20 @@ Instruction *InstCombiner::visitCastInst(CastInst &CI) {
   return 0;
 }
 
+Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
+  if (ConstantBool *C = dyn_cast<ConstantBool>(SI.getCondition()))
+    if (C == ConstantBool::True)
+      return ReplaceInstUsesWith(SI, SI.getTrueValue());
+    else {
+      assert(C == ConstantBool::False);
+      return ReplaceInstUsesWith(SI, SI.getFalseValue());
+    }
+  // Other transformations are possible!
+
+  return 0;
+}
+
+
 // CallInst simplification
 //
 Instruction *InstCombiner::visitCallInst(CallInst &CI) {