From 044eb2f6afba375a914ac9d8024f8f5142bb912e Mon Sep 17 00:00:00 2001
From: Dimitry Andric <dim@FreeBSD.org>
Date: Mon, 18 Dec 2017 20:10:56 +0000
Subject: Vendor import of llvm trunk r321017:
 https://llvm.org/svn/llvm-project/llvm/trunk@321017

---
 lib/Target/PowerPC/PPCLoopPreIncPrep.cpp | 65 ++++++++++++++++++++++++++++++++
 1 file changed, 65 insertions(+)

(limited to 'lib/Target/PowerPC/PPCLoopPreIncPrep.cpp')

diff --git a/lib/Target/PowerPC/PPCLoopPreIncPrep.cpp b/lib/Target/PowerPC/PPCLoopPreIncPrep.cpp
index a349fa1b40907..cdf544bdfac35 100644
--- a/lib/Target/PowerPC/PPCLoopPreIncPrep.cpp
+++ b/lib/Target/PowerPC/PPCLoopPreIncPrep.cpp
@@ -28,6 +28,7 @@
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/SmallSet.h"
 #include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/Statistic.h"
 #include "llvm/Analysis/LoopInfo.h"
 #include "llvm/Analysis/ScalarEvolution.h"
 #include "llvm/Analysis/ScalarEvolutionExpander.h"
@@ -61,6 +62,8 @@ static cl::opt<unsigned> MaxVars("ppc-preinc-prep-max-vars",
                                  cl::Hidden, cl::init(16),
   cl::desc("Potential PHI threshold for PPC preinc loop prep"));
 
+STATISTIC(PHINodeAlreadyExists, "PHI node already in pre-increment form");
+
 namespace llvm {
 
   void initializePPCLoopPreIncPrepPass(PassRegistry&);
@@ -88,6 +91,9 @@ namespace {
       AU.addRequired<ScalarEvolutionWrapperPass>();
     }
 
+    bool alreadyPrepared(Loop *L, Instruction* MemI,
+                         const SCEV *BasePtrStartSCEV,
+                         const SCEVConstant *BasePtrIncSCEV);
     bool runOnFunction(Function &F) override;
 
     bool runOnLoop(Loop *L);
@@ -177,6 +183,62 @@ bool PPCLoopPreIncPrep::runOnFunction(Function &F) {
   return MadeChange;
 }
 
+// In order to prepare for the pre-increment a PHI is added.
+// This function will check to see if that PHI already exists and will return
+//  true if it found an existing PHI with the same start and increment as the
+//  one we wanted to create.
+bool PPCLoopPreIncPrep::alreadyPrepared(Loop *L, Instruction* MemI,
+                                        const SCEV *BasePtrStartSCEV,
+                                        const SCEVConstant *BasePtrIncSCEV) {
+  BasicBlock *BB = MemI->getParent();
+  if (!BB)
+    return false;
+
+  BasicBlock *PredBB = L->getLoopPredecessor();
+  BasicBlock *LatchBB = L->getLoopLatch();
+
+  if (!PredBB || !LatchBB)
+    return false;
+
+  // Run through the PHIs and see if we have some that looks like a preparation
+  iterator_range<BasicBlock::phi_iterator> PHIIter = BB->phis();
+  for (auto & CurrentPHI : PHIIter) {
+    PHINode *CurrentPHINode = dyn_cast<PHINode>(&CurrentPHI);
+    if (!CurrentPHINode)
+      continue;
+
+    if (!SE->isSCEVable(CurrentPHINode->getType()))
+      continue;
+
+    const SCEV *PHISCEV = SE->getSCEVAtScope(CurrentPHINode, L);
+
+    const SCEVAddRecExpr *PHIBasePtrSCEV = dyn_cast<SCEVAddRecExpr>(PHISCEV);
+    if (!PHIBasePtrSCEV)
+      continue;
+
+    const SCEVConstant *PHIBasePtrIncSCEV =
+      dyn_cast<SCEVConstant>(PHIBasePtrSCEV->getStepRecurrence(*SE));
+    if (!PHIBasePtrIncSCEV)
+      continue;
+
+    if (CurrentPHINode->getNumIncomingValues() == 2) {
+      if ( (CurrentPHINode->getIncomingBlock(0) == LatchBB &&
+            CurrentPHINode->getIncomingBlock(1) == PredBB) ||
+            (CurrentPHINode->getIncomingBlock(1) == LatchBB &&
+            CurrentPHINode->getIncomingBlock(0) == PredBB) ) {
+        if (PHIBasePtrSCEV->getStart() == BasePtrStartSCEV &&
+            PHIBasePtrIncSCEV == BasePtrIncSCEV) {
+          // The existing PHI (CurrentPHINode) has the same start and increment
+          //  as the PHI that we wanted to create.
+          ++PHINodeAlreadyExists;
+          return true;
+        }
+      }
+    }
+  }
+  return false;
+}
+
 bool PPCLoopPreIncPrep::runOnLoop(Loop *L) {
   bool MadeChange = false;
 
@@ -347,6 +409,9 @@ bool PPCLoopPreIncPrep::runOnLoop(Loop *L) {
 
     DEBUG(dbgs() << "PIP: New start is: " << *BasePtrStartSCEV << "\n");
 
+    if (alreadyPrepared(L, MemI, BasePtrStartSCEV, BasePtrIncSCEV))
+      continue;
+
     PHINode *NewPHI = PHINode::Create(I8PtrTy, HeaderLoopPredCount,
       MemI->hasName() ? MemI->getName() + ".phi" : "",
       Header->getFirstNonPHI());
-- 
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