From 96a52a6f6ccc63e3cb636e218a5cf7f1c5691e83 Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Thu, 9 Dec 2004 07:14:34 +0000
Subject: [PATCH] Implement trivial sinking for load instructions.  This causes
 us to sink 567 loads in spec

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@18692 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Scalar/InstructionCombining.cpp | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index 9e37d96f59e..40b2d485437 100644
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -4206,7 +4206,17 @@ static bool TryToSinkInstruction(Instruction *I, BasicBlock *DestBlock) {
   if (isa<AllocaInst>(I) && I->getParent() == &DestBlock->getParent()->front())
     return false;
 
-  if (isa<LoadInst>(I)) return false;
+  // We can only sink load instructions if there is nothing between the load and
+  // the end of block that could change the value.
+  if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
+    if (LI->isVolatile()) return false;  // Don't sink volatile loads.
+
+    for (BasicBlock::iterator Scan = LI, E = LI->getParent()->end();
+         Scan != E; ++Scan)
+      if (Scan->mayWriteToMemory())
+        return false;
+    std::cerr << "SUNK LOAD: " << *LI;
+  }
 
   BasicBlock::iterator InsertPos = DestBlock->begin();
   while (isa<PHINode>(InsertPos)) ++InsertPos;