Allow LLE/LD and the loop versioning infrastructure to use SCEV predicates

Summary:
LAA currently generates a set of SCEV predicates that must be checked by users.
In the case of Loop Distribute/Loop Load Elimination, no such predicates could have
been emitted, since we don't allow stride versioning. However, in the future there
could be SCEV predicates that will need to be checked.

This change adds support for SCEV predicate versioning in the Loop Distribute, Loop
Load Eliminate and the loop versioning infrastructure.

Reviewers: anemet

Subscribers: mssimpso, sanjoy, llvm-commits

Differential Revision: http://reviews.llvm.org/D14240

llvm-svn: 252467

1 files changed, 53 insertions, 22 deletions

diff --git a/llvm/lib/Transforms/Utils/LoopVersioning.cpp b/llvm/lib/Transforms/Utils/LoopVersioning.cpp
index bf7ed73..a77c364 100644
--- a/llvm/lib/Transforms/Utils/LoopVersioning.cpp
+++ b/llvm/lib/Transforms/Utils/LoopVersioning.cpp
@@ -17,46 +17,78 @@
 
 #include "llvm/Analysis/LoopAccessAnalysis.h"
 #include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/ScalarEvolutionExpander.h"
 #include "llvm/IR/Dominators.h"
 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
 #include "llvm/Transforms/Utils/Cloning.h"
 
 using namespace llvm;
 
-LoopVersioning::LoopVersioning(
-    SmallVector<RuntimePointerChecking::PointerCheck, 4> Checks,
-    const LoopAccessInfo &LAI, Loop *L, LoopInfo *LI, DominatorTree *DT)
-    : VersionedLoop(L), NonVersionedLoop(nullptr), Checks(std::move(Checks)),
-      LAI(LAI), LI(LI), DT(DT) {
+LoopVersioning::LoopVersioning(const LoopAccessInfo &LAI, Loop *L, LoopInfo *LI,
+                               DominatorTree *DT, ScalarEvolution *SE,
+                               bool UseLAIChecks)
+    : VersionedLoop(L), NonVersionedLoop(nullptr), LAI(LAI), LI(LI), DT(DT),
+      SE(SE) {
   assert(L->getExitBlock() && "No single exit block");
   assert(L->getLoopPreheader() && "No preheader");
+  if (UseLAIChecks) {
+    setAliasChecks(LAI.getRuntimePointerChecking()->getChecks());
+    setSCEVChecks(LAI.Preds);
+  }
 }
 
-LoopVersioning::LoopVersioning(const LoopAccessInfo &LAInfo, Loop *L,
-                               LoopInfo *LI, DominatorTree *DT)
-    : VersionedLoop(L), NonVersionedLoop(nullptr),
-      Checks(LAInfo.getRuntimePointerChecking()->getChecks()), LAI(LAInfo),
-      LI(LI), DT(DT) {
-  assert(L->getExitBlock() && "No single exit block");
-  assert(L->getLoopPreheader() && "No preheader");
+void LoopVersioning::setAliasChecks(
+    const SmallVector<RuntimePointerChecking::PointerCheck, 4> Checks) {
+  AliasChecks = std::move(Checks);
+}
+
+void LoopVersioning::setSCEVChecks(SCEVUnionPredicate Check) {
+  Preds = std::move(Check);
 }
 
 void LoopVersioning::versionLoop(
     const SmallVectorImpl<Instruction *> &DefsUsedOutside) {
   Instruction *FirstCheckInst;
   Instruction *MemRuntimeCheck;
+  Value *SCEVRuntimeCheck;
+  Value *RuntimeCheck = nullptr;
+
   // Add the memcheck in the original preheader (this is empty initially).
-  BasicBlock *MemCheckBB = VersionedLoop->getLoopPreheader();
+  BasicBlock *RuntimeCheckBB = VersionedLoop->getLoopPreheader();
   std::tie(FirstCheckInst, MemRuntimeCheck) =
-      LAI.addRuntimeChecks(MemCheckBB->getTerminator(), Checks);
+      LAI.addRuntimeChecks(RuntimeCheckBB->getTerminator(), AliasChecks);
   assert(MemRuntimeCheck && "called even though needsAnyChecking = false");
 
+  const SCEVUnionPredicate &Pred = LAI.Preds;
+  SCEVExpander Exp(*SE, RuntimeCheckBB->getModule()->getDataLayout(),
+                   "scev.check");
+  SCEVRuntimeCheck =
+      Exp.expandCodeForPredicate(&Pred, RuntimeCheckBB->getTerminator());
+  auto *CI = dyn_cast<ConstantInt>(SCEVRuntimeCheck);
+
+  // Discard the SCEV runtime check if it is always true.
+  if (CI && CI->isZero())
+    SCEVRuntimeCheck = nullptr;
+
+  if (MemRuntimeCheck && SCEVRuntimeCheck) {
+    RuntimeCheck = BinaryOperator::Create(Instruction::Or, MemRuntimeCheck,
+                                          SCEVRuntimeCheck, "ldist.safe");
+    if (auto *I = dyn_cast<Instruction>(RuntimeCheck))
+      I->insertBefore(RuntimeCheckBB->getTerminator());
+  } else
+    RuntimeCheck = MemRuntimeCheck ? MemRuntimeCheck : SCEVRuntimeCheck;
+
+  assert(RuntimeCheck && "called even though we don't need "
+                         "any runtime checks");
+
   // Rename the block to make the IR more readable.
-  MemCheckBB->setName(VersionedLoop->getHeader()->getName() + ".lver.memcheck");
+  RuntimeCheckBB->setName(VersionedLoop->getHeader()->getName() +
+                          ".lver.check");
 
   // Create empty preheader for the loop (and after cloning for the
   // non-versioned loop).
-  BasicBlock *PH = SplitBlock(MemCheckBB, MemCheckBB->getTerminator(), DT, LI);
+  BasicBlock *PH =
+      SplitBlock(RuntimeCheckBB, RuntimeCheckBB->getTerminator(), DT, LI);
   PH->setName(VersionedLoop->getHeader()->getName() + ".ph");
 
   // Clone the loop including the preheader.
@@ -65,20 +97,19 @@ void LoopVersioning::versionLoop(
   // block is a join between the two loops.
   SmallVector<BasicBlock *, 8> NonVersionedLoopBlocks;
   NonVersionedLoop =
-      cloneLoopWithPreheader(PH, MemCheckBB, VersionedLoop, VMap, ".lver.orig",
-                             LI, DT, NonVersionedLoopBlocks);
+      cloneLoopWithPreheader(PH, RuntimeCheckBB, VersionedLoop, VMap,
+                             ".lver.orig", LI, DT, NonVersionedLoopBlocks);
   remapInstructionsInBlocks(NonVersionedLoopBlocks, VMap);
 
   // Insert the conditional branch based on the result of the memchecks.
-  Instruction *OrigTerm = MemCheckBB->getTerminator();
+  Instruction *OrigTerm = RuntimeCheckBB->getTerminator();
   BranchInst::Create(NonVersionedLoop->getLoopPreheader(),
-                     VersionedLoop->getLoopPreheader(), MemRuntimeCheck,
-                     OrigTerm);
+                     VersionedLoop->getLoopPreheader(), RuntimeCheck, OrigTerm);
   OrigTerm->eraseFromParent();
 
   // The loops merge in the original exit block.  This is now dominated by the
   // memchecking block.
-  DT->changeImmediateDominator(VersionedLoop->getExitBlock(), MemCheckBB);
+  DT->changeImmediateDominator(VersionedLoop->getExitBlock(), RuntimeCheckBB);
 
   // Adds the necessary PHI nodes for the versioned loops based on the
   // loop-defined values used outside of the loop.