From 1d665c9a9fb32c3d6483fa146ba85d03b1e9d97f Mon Sep 17 00:00:00 2001
From: Nick Lewycky <nicholas@mxc.ca>
Date: Fri, 17 Jun 2011 10:09:00 +0000
Subject: When promoting an alloca to registers discard any lifetime
 intrinsics.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@133251 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Utils/PromoteMemoryToRegister.cpp | 59 ++++++++++++++++++++++++
 1 file changed, 59 insertions(+)

diff --git a/lib/Transforms/Utils/PromoteMemoryToRegister.cpp b/lib/Transforms/Utils/PromoteMemoryToRegister.cpp
index a1736b931f..32d1dcccd2 100644
--- a/lib/Transforms/Utils/PromoteMemoryToRegister.cpp
+++ b/lib/Transforms/Utils/PromoteMemoryToRegister.cpp
@@ -73,6 +73,22 @@ struct DenseMapInfo<std::pair<BasicBlock*, unsigned> > {
 };
 }
 
+/// onlyUsedByLifetimeMarkers - Return true if the only users of this pointer
+/// are lifetime markers.
+///
+static bool onlyUsedByLifetimeMarkers(const Value *V) {
+  for (Value::const_use_iterator UI = V->use_begin(), UE = V->use_end();
+       UI != UE; ++UI) {
+    const IntrinsicInst *II = dyn_cast<IntrinsicInst>(*UI);
+    if (!II) return false;
+
+    if (II->getIntrinsicID() != Intrinsic::lifetime_start &&
+        II->getIntrinsicID() != Intrinsic::lifetime_end)
+      return false;
+  }
+  return true;
+}
+
 /// isAllocaPromotable - Return true if this alloca is legal for promotion.
 /// This is true if there are only loads and stores to the alloca.
 ///
@@ -92,6 +108,22 @@ bool llvm::isAllocaPromotable(const AllocaInst *AI) {
         return false;   // Don't allow a store OF the AI, only INTO the AI.
       if (SI->isVolatile())
         return false;
+    } else if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(U)) {
+      if (II->getIntrinsicID() != Intrinsic::lifetime_start &&
+          II->getIntrinsicID() != Intrinsic::lifetime_end)
+        return false;
+    } else if (const BitCastInst *BCI = dyn_cast<BitCastInst>(U)) {
+      if (BCI->getType() != Type::getInt8PtrTy(U->getContext()))
+        return false;
+      if (!onlyUsedByLifetimeMarkers(BCI))
+        return false;
+    } else if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U)) {
+      if (GEPI->getType() != Type::getInt8PtrTy(U->getContext()))
+        return false;
+      if (!GEPI->hasAllZeroIndices())
+        return false;
+      if (!onlyUsedByLifetimeMarkers(GEPI))
+        return false;
     } else {
       return false;
     }
@@ -335,6 +367,31 @@ namespace {
   };
 }  // end of anonymous namespace
 
+static void removeLifetimeIntrinsicUsers(AllocaInst *AI) {
+  // Knowing that this alloca is promotable, we know that it's safe to kill all
+  // instructions except for load and store.
+
+  for (Value::use_iterator UI = AI->use_begin(), UE = AI->use_end();
+       UI != UE;) {
+    Instruction *I = cast<Instruction>(*UI);
+    ++UI;
+    if (isa<LoadInst>(I) || isa<StoreInst>(I))
+      continue;
+
+    if (!I->getType()->isVoidTy()) {
+      // The only users of this bitcast/GEP instruction are lifetime intrinsics.
+      // Follow the use/def chain to erase them now instead of leaving it for
+      // dead code elimination later.
+      for (Value::use_iterator UI = I->use_begin(), UE = I->use_end();
+           UI != UE;) {
+        Instruction *Inst = cast<Instruction>(*UI);
+        ++UI;
+        Inst->eraseFromParent();
+      }
+    }
+    I->eraseFromParent();
+  }
+}
 
 void PromoteMem2Reg::run() {
   Function &F = *DT.getRoot()->getParent();
@@ -353,6 +410,8 @@ void PromoteMem2Reg::run() {
     assert(AI->getParent()->getParent() == &F &&
            "All allocas should be in the same function, which is same as DF!");
 
+    removeLifetimeIntrinsicUsers(AI);
+
     if (AI->use_empty()) {
       // If there are no uses of the alloca, just delete it now.
       if (AST) AST->deleteValue(AI);
-- 
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