Add a new attribute, 'noduplicate'. If a function contains a noduplicate call, the call cannot be duplicated - Jump threading, loop unrolling, loop unswitching, and loop rotation are inhibited if they would duplicate the call.

Similarly inlining of the function is inhibited, if that would duplicate the call (in particular inlining is still allowed when there is only one callsite and the function has internal linkage).

llvm-svn: 170704

4 files changed, 29 insertions, 4 deletions

diff --git a/llvm/lib/Transforms/Scalar/JumpThreading.cpp b/llvm/lib/Transforms/Scalar/JumpThreading.cpp
index 4a4cd705e21..c004c9a1a7d 100644
--- a/llvm/lib/Transforms/Scalar/JumpThreading.cpp
+++ b/llvm/lib/Transforms/Scalar/JumpThreading.cpp
@@ -249,7 +249,11 @@ static unsigned getJumpThreadDuplicationCost(const BasicBlock *BB,
     // as having cost of 2 total, and if they are a vector intrinsic, we model
     // them as having cost 1.
     if (const CallInst *CI = dyn_cast<CallInst>(I)) {
-      if (!isa<IntrinsicInst>(CI))
+      if (CI->hasFnAttr(Attribute::NoDuplicate))
+        // Blocks with NoDuplicate are modelled as having infinite cost, so they
+        // are never duplicated.
+        return ~0U;
+      else if (!isa<IntrinsicInst>(CI))
         Size += 3;
       else if (!CI->getType()->isVectorTy())
         Size += 1;
diff --git a/llvm/lib/Transforms/Scalar/LoopRotation.cpp b/llvm/lib/Transforms/Scalar/LoopRotation.cpp
index 249baf51645..83e049b94c2 100644
--- a/llvm/lib/Transforms/Scalar/LoopRotation.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopRotation.cpp
@@ -274,10 +274,16 @@ bool LoopRotate::rotateLoop(Loop *L) {
   if (OrigLatch == 0 || L->isLoopExiting(OrigLatch))
     return false;
 
-  // Check size of original header and reject loop if it is very big.
+  // Check size of original header and reject loop if it is very big or we can't
+  // duplicate blocks inside it.
   {
     CodeMetrics Metrics;
     Metrics.analyzeBasicBlock(OrigHeader);
+    if (Metrics.notDuplicatable) {
+      DEBUG(dbgs() << "LoopRotation: NOT rotating - contains non duplicatable"
+            << " instructions: "; L->dump());
+      return false;
+    }
     if (Metrics.NumInsts > MAX_HEADER_SIZE)
       return false;
   }
diff --git a/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp b/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
index de6b9952db7..2a04af33d99 100644
--- a/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
@@ -113,12 +113,13 @@ Pass *llvm::createLoopUnrollPass(int Threshold, int Count, int AllowPartial) {
 
 /// ApproximateLoopSize - Approximate the size of the loop.
 static unsigned ApproximateLoopSize(const Loop *L, unsigned &NumCalls,
-                                    const DataLayout *TD) {
+                                    bool &NotDuplicatable, const DataLayout *TD) {
   CodeMetrics Metrics;
   for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
        I != E; ++I)
     Metrics.analyzeBasicBlock(*I, TD);
   NumCalls = Metrics.NumInlineCandidates;
+  NotDuplicatable = Metrics.notDuplicatable;
 
   unsigned LoopSize = Metrics.NumInsts;
 
@@ -181,8 +182,15 @@ bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) {
   if (Threshold != NoThreshold) {
     const DataLayout *TD = getAnalysisIfAvailable<DataLayout>();
     unsigned NumInlineCandidates;
-    unsigned LoopSize = ApproximateLoopSize(L, NumInlineCandidates, TD);
+    bool notDuplicatable;
+    unsigned LoopSize = ApproximateLoopSize(L, NumInlineCandidates,
+                                            notDuplicatable, TD);
     DEBUG(dbgs() << "  Loop Size = " << LoopSize << "\n");
+    if (notDuplicatable) {
+      DEBUG(dbgs() << "  Not unrolling loop which contains non duplicatable"
+            << " instructions.\n");
+      return false;
+    }
     if (NumInlineCandidates != 0) {
       DEBUG(dbgs() << "  Not unrolling loop with inlinable calls.\n");
       return false;
diff --git a/llvm/lib/Transforms/Scalar/LoopUnswitch.cpp b/llvm/lib/Transforms/Scalar/LoopUnswitch.cpp
index 17ffda60fdf..e2e42e5054f 100644
--- a/llvm/lib/Transforms/Scalar/LoopUnswitch.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopUnswitch.cpp
@@ -248,6 +248,13 @@ bool LUAnalysisCache::countLoop(const Loop* L) {
     Props.SizeEstimation = std::min(Metrics.NumInsts, Metrics.NumBlocks * 5);
     Props.CanBeUnswitchedCount = MaxSize / (Props.SizeEstimation);
     MaxSize -= Props.SizeEstimation * Props.CanBeUnswitchedCount;
+
+    if (Metrics.notDuplicatable) {
+      DEBUG(dbgs() << "NOT unswitching loop %"
+            << L->getHeader()->getName() << ", contents cannot be "
+            << "duplicated!\n");
+      return false;
+    }
   }
 
   if (!Props.CanBeUnswitchedCount) {