From 866ed7f63f9edf9c20763a9abc115fb23372f42f Mon Sep 17 00:00:00 2001
From: Owen Anderson <resistor@mac.com>
Date: Mon, 26 May 2014 08:58:51 +0000
Subject: [PATCH] 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
---
 include/llvm/Transforms/Scalar.h       |  2 +-
 lib/Transforms/Scalar/LoopRotation.cpp | 18 ++++++++++++++----
 2 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/include/llvm/Transforms/Scalar.h b/include/llvm/Transforms/Scalar.h
index 68d61bdbdb7..cf1d6554407 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 5c747e1ac51..2ce58314f8e 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;
   }