Add getUnrollingPreferences to TTI

Allow targets to customize the default behavior of the generic loop unrolling
transformation. This will be used by the PowerPC backend when targeting the A2
core (which is in-order with a deep pipeline), and using more aggressive
defaults is important.

llvm-svn: 189565

llvm/include/llvm/Analysis/TargetTransformInfo.h

@@ -191,6 +191,20 @@ public:
   /// incurs significant execution cost.
   virtual bool isLoweredToCall(const Function *F) const;
 
+  /// Parameters that control the generic loop unrolling transformation.
+  struct UnrollingPreferences {
+    unsigned Threshold; ///< The cost threshold for the unrolled loop.
+    unsigned OptSizeThreshold; ///< The cost threshold for the unrolled loop
+                               ///< when optimizing for size.
+    bool     Partial;   ///< Allow partial loop unrolling.
+    bool     Runtime;   ///< Perform runtime unrolling.
+  };
+
+  /// \brief Get target-customized preferences for the generic loop unrolling
+  /// transformation. Returns true if the UnrollingPreferences struct has been
+  /// initialized.
+  virtual bool getUnrollingPreferences(UnrollingPreferences &UP) const;
+
   /// @}
 
   /// \name Scalar Target Information

llvm/lib/Analysis/TargetTransformInfo.cpp

@@ -96,6 +96,11 @@ bool TargetTransformInfo::isLoweredToCall(const Function *F) const {
   return PrevTTI->isLoweredToCall(F);
 }
 
+bool TargetTransformInfo::getUnrollingPreferences(
+                            UnrollingPreferences &UP) const {
+  return PrevTTI->getUnrollingPreferences(UP);
+}
+
 bool TargetTransformInfo::isLegalAddImmediate(int64_t Imm) const {
   return PrevTTI->isLegalAddImmediate(Imm);
 }
@@ -469,6 +474,10 @@ struct NoTTI : ImmutablePass, TargetTransformInfo {
     return true;
   }
 
+  virtual bool getUnrollingPreferences(UnrollingPreferences &) const {
+    return false;
+  }
+
   bool isLegalAddImmediate(int64_t Imm) const {
     return false;
   }

llvm/lib/CodeGen/BasicTargetTransformInfo.cpp

@@ -84,6 +84,7 @@ public:
   virtual unsigned getJumpBufSize() const;
   virtual bool shouldBuildLookupTables() const;
   virtual bool haveFastSqrt(Type *Ty) const;
+  virtual bool getUnrollingPreferences(UnrollingPreferences &UP) const;
 
   /// @}
 
@@ -189,6 +190,10 @@ bool BasicTTI::haveFastSqrt(Type *Ty) const {
   return TLI->isTypeLegal(VT) && TLI->isOperationLegalOrCustom(ISD::FSQRT, VT);
 }
 
+bool BasicTTI::getUnrollingPreferences(UnrollingPreferences &) const {
+  return false;
+}
+
 //===----------------------------------------------------------------------===//
 //
 // Calls used by the vectorizers.

llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp

@@ -55,6 +55,8 @@ namespace {
       CurrentAllowPartial = (P == -1) ? UnrollAllowPartial : (bool)P;
 
       UserThreshold = (T != -1) || (UnrollThreshold.getNumOccurrences() > 0);
+      UserAllowPartial = (P != -1) ||
+                         (UnrollAllowPartial.getNumOccurrences() > 0);
 
       initializeLoopUnrollPass(*PassRegistry::getPassRegistry());
     }
@@ -76,6 +78,7 @@ namespace {
     unsigned CurrentThreshold;
     bool     CurrentAllowPartial;
     bool     UserThreshold;        // CurrentThreshold is user-specified.
+    bool     UserAllowPartial;     // CurrentAllowPartial is user-specified.
 
     bool runOnLoop(Loop *L, LPPassManager &LPM);
 
@@ -145,16 +148,20 @@ bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) {
         << "] Loop %" << Header->getName() << "\n");
   (void)Header;
 
+  TargetTransformInfo::UnrollingPreferences UP;
+  bool HasUP = TTI.getUnrollingPreferences(UP);
+
   // Determine the current unrolling threshold.  While this is normally set
   // from UnrollThreshold, it is overridden to a smaller value if the current
   // function is marked as optimize-for-size, and the unroll threshold was
   // not user specified.
-  unsigned Threshold = CurrentThreshold;
+  unsigned Threshold = (HasUP && !UserThreshold) ? UP.Threshold :
+                                                   CurrentThreshold;
   if (!UserThreshold &&
       Header->getParent()->getAttributes().
         hasAttribute(AttributeSet::FunctionIndex,
                      Attribute::OptimizeForSize))
-    Threshold = OptSizeUnrollThreshold;
+    Threshold = HasUP ? UP.OptSizeThreshold : OptSizeUnrollThreshold;
 
   // Find trip count and trip multiple if count is not available
   unsigned TripCount = 0;
@@ -184,6 +191,9 @@ bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) {
     Count = TripCount;
   }
 
+  bool Runtime = (HasUP && UnrollRuntime.getNumOccurrences() == 0) ?
+                 UP.Runtime : UnrollRuntime;
+
   // Enforce the threshold.
   if (Threshold != NoThreshold) {
     unsigned NumInlineCandidates;
@@ -204,7 +214,9 @@ bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) {
     if (TripCount != 1 && Size > Threshold) {
       DEBUG(dbgs() << "  Too large to fully unroll with count: " << Count
             << " because size: " << Size << ">" << Threshold << "\n");
-      if (!CurrentAllowPartial && !(UnrollRuntime && TripCount == 0)) {
+      bool AllowPartial = (HasUP && !UserAllowPartial) ? UP.Partial :
+                                                         CurrentAllowPartial;
+      if (!AllowPartial && !(Runtime && TripCount == 0)) {
         DEBUG(dbgs() << "  will not try to unroll partially because "
               << "-unroll-allow-partial not given\n");
         return false;
@@ -215,7 +227,7 @@ bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) {
         while (Count != 0 && TripCount%Count != 0)
           Count--;
       }
-      else if (UnrollRuntime) {
+      else if (Runtime) {
         // Reduce unroll count to be a lower power-of-two value
         while (Count != 0 && Size > Threshold) {
           Count >>= 1;
@@ -231,7 +243,7 @@ bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) {
   }
 
   // Unroll the loop.
-  if (!UnrollLoop(L, Count, TripCount, UnrollRuntime, TripMultiple, LI, &LPM))
+  if (!UnrollLoop(L, Count, TripCount, Runtime, TripMultiple, LI, &LPM))
     return false;
 
   return true;