Generalize MemCpyOpt's handling of call slot forwarding to function properly when the call slot

forwarding is implemented with a load/store pair rather than a memcpy.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@116637 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 48 insertions, 18 deletions

diff --git a/lib/Transforms/Scalar/MemCpyOptimizer.cpp b/lib/Transforms/Scalar/MemCpyOptimizer.cpp
index d4d4b57692..e4f329fdad 100644
--- a/lib/Transforms/Scalar/MemCpyOptimizer.cpp
+++ b/lib/Transforms/Scalar/MemCpyOptimizer.cpp
@@ -321,7 +321,8 @@ namespace {
     bool processStore(StoreInst *SI, BasicBlock::iterator &BBI);
     bool processMemCpy(MemCpyInst *M);
     bool processMemMove(MemMoveInst *M);
-    bool performCallSlotOptzn(MemCpyInst *cpy, CallInst *C);
+    bool performCallSlotOptzn(Instruction *cpy, Value *cpyDst, Value *cpySrc,
+                              uint64_t cpyLen, CallInst *C);
     bool iterateOnFunction(Function &F);
   };
   
@@ -339,7 +340,6 @@ INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
 INITIALIZE_PASS_END(MemCpyOpt, "memcpyopt", "MemCpy Optimization",
                     false, false)
 
-
 /// processStore - When GVN is scanning forward over instructions, we look for
 /// some other patterns to fold away.  In particular, this looks for stores to
 /// neighboring locations of memory.  If it sees enough consequtive ones
@@ -347,6 +347,37 @@ INITIALIZE_PASS_END(MemCpyOpt, "memcpyopt", "MemCpy Optimization",
 bool MemCpyOpt::processStore(StoreInst *SI, BasicBlock::iterator &BBI) {
   if (SI->isVolatile()) return false;
   
+  TargetData *TD = getAnalysisIfAvailable<TargetData>();
+  if (!TD) return false;
+
+  // Detect cases where we're performing call slot forwarding, but
+  // happen to be using a load-store pair to implement it, rather than
+  // a memcpy.
+  if (LoadInst *LI = dyn_cast<LoadInst>(SI->getOperand(0))) {
+    if (!LI->isVolatile() && LI->hasOneUse()) {
+      MemoryDependenceAnalysis &MD = getAnalysis<MemoryDependenceAnalysis>();
+
+      MemDepResult dep = MD.getDependency(LI);
+      CallInst *C = 0;
+      if (dep.isClobber() && !isa<MemCpyInst>(dep.getInst()))
+        C = dyn_cast<CallInst>(dep.getInst());
+      
+      if (C) {
+        bool changed = performCallSlotOptzn(LI,
+                        SI->getPointerOperand()->stripPointerCasts(), 
+                        LI->getPointerOperand()->stripPointerCasts(),
+                        TD->getTypeStoreSize(SI->getOperand(0)->getType()), C);
+        if (changed) {
+          MD.removeInstruction(SI);
+          SI->eraseFromParent();
+          LI->eraseFromParent();
+          ++NumMemCpyInstr;
+          return true;
+        }
+      }
+    }
+  }
+  
   LLVMContext &Context = SI->getContext();
 
   // There are two cases that are interesting for this code to handle: memcpy
@@ -359,8 +390,6 @@ bool MemCpyOpt::processStore(StoreInst *SI, BasicBlock::iterator &BBI) {
   if (!ByteVal)
     return false;
 
-  TargetData *TD = getAnalysisIfAvailable<TargetData>();
-  if (!TD) return false;
   AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
   Module *M = SI->getParent()->getParent()->getParent();
 
@@ -494,7 +523,9 @@ bool MemCpyOpt::processStore(StoreInst *SI, BasicBlock::iterator &BBI) {
 /// performCallSlotOptzn - takes a memcpy and a call that it depends on,
 /// and checks for the possibility of a call slot optimization by having
 /// the call write its result directly into the destination of the memcpy.
-bool MemCpyOpt::performCallSlotOptzn(MemCpyInst *cpy, CallInst *C) {
+bool MemCpyOpt::performCallSlotOptzn(Instruction *cpy,
+                                     Value *cpyDest, Value *cpySrc,
+                                     uint64_t cpyLen, CallInst *C) {
   // The general transformation to keep in mind is
   //
   //   call @func(..., src, ...)
@@ -511,16 +542,8 @@ bool MemCpyOpt::performCallSlotOptzn(MemCpyInst *cpy, CallInst *C) {
 
   // Deliberately get the source and destination with bitcasts stripped away,
   // because we'll need to do type comparisons based on the underlying type.
-  Value *cpyDest = cpy->getDest();
-  Value *cpySrc = cpy->getSource();
   CallSite CS(C);
 
-  // We need to be able to reason about the size of the memcpy, so we require
-  // that it be a constant.
-  ConstantInt *cpyLength = dyn_cast<ConstantInt>(cpy->getLength());
-  if (!cpyLength)
-    return false;
-
   // Require that src be an alloca.  This simplifies the reasoning considerably.
   AllocaInst *srcAlloca = dyn_cast<AllocaInst>(cpySrc);
   if (!srcAlloca)
@@ -537,7 +560,7 @@ bool MemCpyOpt::performCallSlotOptzn(MemCpyInst *cpy, CallInst *C) {
   uint64_t srcSize = TD->getTypeAllocSize(srcAlloca->getAllocatedType()) *
     srcArraySize->getZExtValue();
 
-  if (cpyLength->getZExtValue() < srcSize)
+  if (cpyLen < srcSize)
     return false;
 
   // Check that accessing the first srcSize bytes of dest will not cause a
@@ -606,7 +629,7 @@ bool MemCpyOpt::performCallSlotOptzn(MemCpyInst *cpy, CallInst *C) {
   // the use analysis, we also need to know that it does not sneakily
   // access dest.  We rely on AA to figure this out for us.
   AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
-  if (AA.getModRefInfo(C, cpy->getRawDest(), srcSize) !=
+  if (AA.getModRefInfo(C, cpyDest, srcSize) !=
       AliasAnalysis::NoModRef)
     return false;
 
@@ -635,7 +658,6 @@ bool MemCpyOpt::performCallSlotOptzn(MemCpyInst *cpy, CallInst *C) {
 
   // Remove the memcpy
   MD.removeInstruction(cpy);
-  cpy->eraseFromParent();
   ++NumMemCpyInstr;
 
   return true;
@@ -649,6 +671,10 @@ bool MemCpyOpt::performCallSlotOptzn(MemCpyInst *cpy, CallInst *C) {
 bool MemCpyOpt::processMemCpy(MemCpyInst *M) {
   MemoryDependenceAnalysis &MD = getAnalysis<MemoryDependenceAnalysis>();
 
+  // We can only optimize statically-sized memcpy's.
+  ConstantInt *cpyLen = dyn_cast<ConstantInt>(M->getLength());
+  if (!cpyLen) return false;
+
   // The are two possible optimizations we can do for memcpy:
   //   a) memcpy-memcpy xform which exposes redundance for DSE.
   //   b) call-memcpy xform for return slot optimization.
@@ -656,8 +682,12 @@ bool MemCpyOpt::processMemCpy(MemCpyInst *M) {
   if (!dep.isClobber())
     return false;
   if (!isa<MemCpyInst>(dep.getInst())) {
-    if (CallInst *C = dyn_cast<CallInst>(dep.getInst()))
-      return performCallSlotOptzn(M, C);
+    if (CallInst *C = dyn_cast<CallInst>(dep.getInst())) {
+      bool changed = performCallSlotOptzn(M, M->getDest(), M->getSource(),
+                                  cpyLen->getZExtValue(), C);
+      if (changed) M->eraseFromParent();
+      return changed;
+    }
     return false;
   }