Make the LoopRotate pass's maximum header size configurable both programmatically

and via the command line, mirroring similar functionality in LoopUnroll.  In
situations where clients used custom unrolling thresholds, their intent could
previously be foiled by LoopRotate having a hardcoded threshold.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209617 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 15 insertions, 5 deletions

diff --git a/include/llvm/Transforms/Scalar.h b/include/llvm/Transforms/Scalar.h
index 68d61bdbdb..cf1d655440 100644
--- a/include/llvm/Transforms/Scalar.h
+++ b/include/llvm/Transforms/Scalar.h
@@ -155,7 +155,7 @@ Pass *createLoopRerollPass();
 //
 // LoopRotate - This pass is a simple loop rotating pass.
 //
-Pass *createLoopRotatePass();
+Pass *createLoopRotatePass(int MaxHeaderSize = -1);
 
 //===----------------------------------------------------------------------===//
 //
diff --git a/lib/Transforms/Scalar/LoopRotation.cpp b/lib/Transforms/Scalar/LoopRotation.cpp
index 5c747e1ac5..2ce58314f8 100644
--- a/lib/Transforms/Scalar/LoopRotation.cpp
+++ b/lib/Transforms/Scalar/LoopRotation.cpp
@@ -23,6 +23,7 @@
 #include "llvm/IR/Dominators.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/IntrinsicInst.h"
+#include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
 #include "llvm/Transforms/Utils/Local.h"
@@ -32,7 +33,9 @@ using namespace llvm;
 
 #define DEBUG_TYPE "loop-rotate"
 
-#define MAX_HEADER_SIZE 16
+static cl::opt<unsigned>
+DefaultRotationThreshold("rotation-max-header-size", cl::init(16), cl::Hidden,
+       cl::desc("The default maximum header size for automatic loop rotation"));
 
 STATISTIC(NumRotated, "Number of loops rotated");
 namespace {
@@ -40,8 +43,12 @@ namespace {
   class LoopRotate : public LoopPass {
   public:
     static char ID; // Pass ID, replacement for typeid
-    LoopRotate() : LoopPass(ID) {
+    LoopRotate(int SpecifiedMaxHeaderSize = -1) : LoopPass(ID) {
       initializeLoopRotatePass(*PassRegistry::getPassRegistry());
+      if (SpecifiedMaxHeaderSize == -1)
+        MaxHeaderSize = DefaultRotationThreshold;
+      else
+        MaxHeaderSize = unsigned(SpecifiedMaxHeaderSize);
     }
 
     // LCSSA form makes instruction renaming easier.
@@ -62,6 +69,7 @@ namespace {
     bool rotateLoop(Loop *L, bool SimplifiedLatch);
 
   private:
+    unsigned MaxHeaderSize;
     LoopInfo *LI;
     const TargetTransformInfo *TTI;
   };
@@ -75,7 +83,9 @@ INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
 INITIALIZE_PASS_DEPENDENCY(LCSSA)
 INITIALIZE_PASS_END(LoopRotate, "loop-rotate", "Rotate Loops", false, false)
 
-Pass *llvm::createLoopRotatePass() { return new LoopRotate(); }
+Pass *llvm::createLoopRotatePass(int MaxHeaderSize) {
+  return new LoopRotate(MaxHeaderSize);
+}
 
 /// Rotate Loop L as many times as possible. Return true if
 /// the loop is rotated at least once.
@@ -320,7 +330,7 @@ bool LoopRotate::rotateLoop(Loop *L, bool SimplifiedLatch) {
             << " instructions: "; L->dump());
       return false;
     }
-    if (Metrics.NumInsts > MAX_HEADER_SIZE)
+    if (Metrics.NumInsts > MaxHeaderSize)
       return false;
   }