Hoist the rest of the logic for promoting single-store allocas into the

helper function. This leaves both trivial cases handled entirely in
helper functions and merely manages the list of allocas to process in
the run method.

The next step will be to handle all of the trivial promotion work prior
to even creating the core class and the subsequent simplifications that
enables.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@186784 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 31 insertions, 23 deletions

diff --git a/lib/Transforms/Utils/PromoteMemoryToRegister.cpp b/lib/Transforms/Utils/PromoteMemoryToRegister.cpp
index f703481e4b..5ee812bbe8 100644
--- a/lib/Transforms/Utils/PromoteMemoryToRegister.cpp
+++ b/lib/Transforms/Utils/PromoteMemoryToRegister.cpp
@@ -339,9 +339,15 @@ static void removeLifetimeIntrinsicUsers(AllocaInst *AI) {
   }
 }
 
-/// If there is only a single store to this value, replace any loads of it that
-/// are directly dominated by the definition with the value stored.
-static void rewriteSingleStoreAlloca(AllocaInst *AI, AllocaInfo &Info,
+/// \brief Rewrite as many loads as possible given a single store.
+///
+/// When there is only a single store, we can use the domtree to trivially
+/// replace all of the dominated loads with the stored value. Do so, and return
+/// true if this has successfully promoted the alloca entirely. If this returns
+/// false there were some loads which were not dominated by the single store
+/// and thus must be phi-ed with undef. We fall back to the standard alloca
+/// promotion algorithm in that case.
+static bool rewriteSingleStoreAlloca(AllocaInst *AI, AllocaInfo &Info,
                                      LargeBlockInfo &LBI,
                                      DominatorTree &DT,
                                      AliasSetTracker *AST) {
@@ -401,6 +407,27 @@ static void rewriteSingleStoreAlloca(AllocaInst *AI, AllocaInfo &Info,
     LI->eraseFromParent();
     LBI.deleteValue(LI);
   }
+
+  // Finally, after the scan, check to see if the store is all that is left.
+  if (!Info.UsingBlocks.empty())
+    return false; // If not, we'll have to fall back for the remainder.
+
+  // Record debuginfo for the store and remove the declaration's
+  // debuginfo.
+  if (DbgDeclareInst *DDI = Info.DbgDeclare) {
+    DIBuilder DIB(*AI->getParent()->getParent()->getParent());
+    ConvertDebugDeclareToDebugValue(DDI, Info.OnlyStore, DIB);
+    DDI->eraseFromParent();
+  }
+  // Remove the (now dead) store and alloca.
+  Info.OnlyStore->eraseFromParent();
+  LBI.deleteValue(Info.OnlyStore);
+
+  if (AST)
+    AST->deleteValue(AI);
+  AI->eraseFromParent();
+  LBI.deleteValue(AI);
+  return true;
 }
 
 namespace {
@@ -537,28 +564,9 @@ void PromoteMem2Reg::run() {
     // If there is only a single store to this value, replace any loads of
     // it that are directly dominated by the definition with the value stored.
     if (Info.DefiningBlocks.size() == 1) {
-      rewriteSingleStoreAlloca(AI, Info, LBI, DT, AST);
-
-      // Finally, after the scan, check to see if the store is all that is left.
-      if (Info.UsingBlocks.empty()) {
-        // Record debuginfo for the store and remove the declaration's
-        // debuginfo.
-        if (DbgDeclareInst *DDI = Info.DbgDeclare) {
-          ConvertDebugDeclareToDebugValue(DDI, Info.OnlyStore, DIB);
-          DDI->eraseFromParent();
-        }
-        // Remove the (now dead) store and alloca.
-        Info.OnlyStore->eraseFromParent();
-        LBI.deleteValue(Info.OnlyStore);
-
-        if (AST)
-          AST->deleteValue(AI);
-        AI->eraseFromParent();
-        LBI.deleteValue(AI);
-
+      if (rewriteSingleStoreAlloca(AI, Info, LBI, DT, AST)) {
         // The alloca has been processed, move on.
         RemoveFromAllocasList(AllocaNum);
-
         ++NumSingleStore;
         continue;
       }