[PATCH] D72714: [ARM][MVE] WIP: Tail-Predication: rematerialise iteration count in exit blocks

[Sjoerd Meijer via Phabricator via llvm-commits]

SjoerdMeijer created this revision.
SjoerdMeijer added reviewers: samparker, dmgreen.
Herald added subscribers: hiraditya, kristof.beyls.
Herald added a project: LLVM.

This is a Work-In-Progress patch showing the usage of helper function rewriteLoopExitValues that is refactored out in D72602 <https://reviews.llvm.org/D72602>. We want to rematerialise the iteration count in exit blocks, so that we can clean-up loop update expressions inside the hardware-loops later in ARMLowOverheadLoops.

TODO:

- This should have just worked, except that LCSSA thinks loops are not in LCSSA form, so I will need to look into that, and
- update test cases as do we remove more SUBs from loops now.


https://reviews.llvm.org/D72714

Files:
  llvm/lib/Target/ARM/MVETailPredication.cpp


Index: llvm/lib/Target/ARM/MVETailPredication.cpp
===================================================================
--- llvm/lib/Target/ARM/MVETailPredication.cpp
+++ llvm/lib/Target/ARM/MVETailPredication.cpp
@@ -35,12 +35,14 @@
 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
 #include "llvm/Analysis/TargetTransformInfo.h"
 #include "llvm/CodeGen/TargetPassConfig.h"
+#include "llvm/InitializePasses.h"
 #include "llvm/IR/IRBuilder.h"
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/IntrinsicsARM.h"
 #include "llvm/IR/PatternMatch.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
+#include "llvm/Transforms/Utils/LoopUtils.h"
 
 using namespace llvm;
 
@@ -56,8 +58,12 @@
 class MVETailPredication : public LoopPass {
   SmallVector<IntrinsicInst*, 4> MaskedInsts;
   Loop *L = nullptr;
+  LoopInfo *LI = nullptr;
+  const DataLayout *DL;
+  DominatorTree *DT = nullptr;
   ScalarEvolution *SE = nullptr;
   TargetTransformInfo *TTI = nullptr;
+  TargetLibraryInfo *TLI = nullptr;
 
 public:
   static char ID;
@@ -69,8 +75,12 @@
     AU.addRequired<LoopInfoWrapperPass>();
     AU.addRequired<TargetPassConfig>();
     AU.addRequired<TargetTransformInfoWrapperPass>();
+    AU.addRequired<DominatorTreeWrapperPass>();
+    AU.addRequired<TargetLibraryInfoWrapperPass>();
     AU.addPreserved<LoopInfoWrapperPass>();
+
     AU.setPreservesCFG();
+    getLoopAnalysisUsage(AU);
   }
 
   bool runOnLoop(Loop *L, LPPassManager&) override;
@@ -128,8 +138,13 @@
   auto &TPC = getAnalysis<TargetPassConfig>();
   auto &TM = TPC.getTM<TargetMachine>();
   auto *ST = &TM.getSubtarget<ARMSubtarget>(F);
+  DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
+  LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
   TTI = &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
   SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
+  auto *TLIP = getAnalysisIfAvailable<TargetLibraryInfoWrapperPass>();
+  TLI = TLIP ? &TLIP->getTLI(*L->getHeader()->getParent()) : nullptr;
+  DL = &L->getHeader()->getModule()->getDataLayout();
   this->L = L;
 
   // The MVE and LOB extensions are combined to enable tail-predication, but
@@ -185,7 +200,18 @@
 
   LLVM_DEBUG(dbgs() << "ARM TP: Running on Loop: " << *L << *Setup << "\n"
              << *Decrement << "\n");
-  return TryConvert(Setup->getArgOperand(0));
+
+   if (TryConvert(Setup->getArgOperand(0))) {
+    SmallVector<WeakTrackingVH, 16> DeadInsts;
+    SCEVExpander Rewriter(*SE, *DL, "mvetp");
+    ReplaceExitVal ReplaceExitValue = AlwaysRepl;
+
+    rewriteLoopExitValues(L, LI, TLI, SE, Rewriter, DT, ReplaceExitValue,
+                          DeadInsts);
+    return true;
+  }
+
+  return false;
 }
 
 bool MVETailPredication::isTailPredicate(Instruction *I, Value *NumElements) {
@@ -549,4 +575,5 @@
 char MVETailPredication::ID = 0;
 
 INITIALIZE_PASS_BEGIN(MVETailPredication, DEBUG_TYPE, DESC, false, false)
+INITIALIZE_PASS_DEPENDENCY(LoopPass)
 INITIALIZE_PASS_END(MVETailPredication, DEBUG_TYPE, DESC, false, false)


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