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

1 files changed, 17 insertions, 3 deletions

diff --git a/llvm/lib/Analysis/InlineCost.cpp b/llvm/lib/Analysis/InlineCost.cpp
index f88cabb6a4a..de89fea1193 100644
--- a/llvm/lib/Analysis/InlineCost.cpp
+++ b/llvm/lib/Analysis/InlineCost.cpp
@@ -54,6 +54,8 @@ class CallAnalyzer : public InstVisitor<CallAnalyzer, bool> {
   bool IsRecursiveCall;
   bool ExposesReturnsTwice;
   bool HasDynamicAlloca;
+  bool ContainsNoDuplicateCall;
+
   /// Number of bytes allocated statically by the callee.
   uint64_t AllocatedSize;
   unsigned NumInstructions, NumVectorInstructions;
@@ -128,8 +130,8 @@ public:
   CallAnalyzer(const DataLayout *TD, Function &Callee, int Threshold)
     : TD(TD), F(Callee), Threshold(Threshold), Cost(0),
       IsCallerRecursive(false), IsRecursiveCall(false),
-      ExposesReturnsTwice(false), HasDynamicAlloca(false), AllocatedSize(0),
-      NumInstructions(0), NumVectorInstructions(0),
+      ExposesReturnsTwice(false), HasDynamicAlloca(false), ContainsNoDuplicateCall(false),
+      AllocatedSize(0), NumInstructions(0), NumVectorInstructions(0),
       FiftyPercentVectorBonus(0), TenPercentVectorBonus(0), VectorBonus(0),
       NumConstantArgs(0), NumConstantOffsetPtrArgs(0), NumAllocaArgs(0),
       NumConstantPtrCmps(0), NumConstantPtrDiffs(0),
@@ -615,6 +617,9 @@ bool CallAnalyzer::visitCallSite(CallSite CS) {
     ExposesReturnsTwice = true;
     return false;
   }
+  if (CS.isCall() &&
+      cast<CallInst>(CS.getInstruction())->hasFnAttr(Attribute::NoDuplicate))
+    ContainsNoDuplicateCall = true;
 
   if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(CS.getInstruction())) {
     switch (II->getIntrinsicID()) {
@@ -842,7 +847,9 @@ bool CallAnalyzer::analyzeCall(CallSite CS) {
 
   // If there is only one call of the function, and it has internal linkage,
   // the cost of inlining it drops dramatically.
-  if (F.hasLocalLinkage() && F.hasOneUse() && &F == CS.getCalledFunction())
+  bool OnlyOneCallAndLocalLinkage = F.hasLocalLinkage() && F.hasOneUse() &&
+    &F == CS.getCalledFunction();
+  if (OnlyOneCallAndLocalLinkage)
     Cost += InlineConstants::LastCallToStaticBonus;
 
   // If the instruction after the call, or if the normal destination of the
@@ -1008,6 +1015,12 @@ bool CallAnalyzer::analyzeCall(CallSite CS) {
     }
   }
 
+  // If this is a noduplicate call, we can still inline as long as 
+  // inlining this would cause the removal of the caller (so the instruction
+  // is not actually duplicated, just moved).
+  if (!OnlyOneCallAndLocalLinkage && ContainsNoDuplicateCall)
+    return false;
+
   Threshold += VectorBonus;
 
   return Cost < Threshold;
@@ -1025,6 +1038,7 @@ void CallAnalyzer::dump() {
   DEBUG_PRINT_STAT(NumInstructionsSimplified);
   DEBUG_PRINT_STAT(SROACostSavings);
   DEBUG_PRINT_STAT(SROACostSavingsLost);
+  DEBUG_PRINT_STAT(ContainsNoDuplicateCall);
 #undef DEBUG_PRINT_STAT
 }
 #endif