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.

llvm-svn: 209617

1 files changed, 14 insertions, 4 deletions

diff --git a/llvm/lib/Transforms/Scalar/LoopRotation.cpp b/llvm/lib/Transforms/Scalar/LoopRotation.cpp
index 5c747e1ac51..2ce58314f8e 100644
--- a/llvm/lib/Transforms/Scalar/LoopRotation.cpp
+++ b/llvm/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;
   }