[LCSSA] Implement linear algorithm for the isRecursivelyLCSSAForm

For each block check that it doesn't have any uses outside of it's innermost loop.

Differential Revision: https://reviews.llvm.org/D25364

llvm-svn: 283877

llvm/include/llvm/Analysis/LoopInfo.h

@@ -412,7 +412,7 @@ class Loop : public LoopBase<BasicBlock, Loop> {
   bool isLCSSAForm(DominatorTree &DT) const;
 
   /// Return true if this Loop and all inner subloops are in LCSSA form.
-  bool isRecursivelyLCSSAForm(DominatorTree &DT) const;
+  bool isRecursivelyLCSSAForm(DominatorTree &DT, const LoopInfo &LI) const;
 
   /// Return true if the Loop is in the form that the LoopSimplify form
   /// transforms loops to, which is sometimes called normal form.

llvm/lib/Analysis/LoopInfo.cpp

@@ -143,42 +143,48 @@ PHINode *Loop::getCanonicalInductionVariable() const {
   return nullptr;
 }
 
-bool Loop::isLCSSAForm(DominatorTree &DT) const {
-  for (BasicBlock *BB : this->blocks()) {
-    for (Instruction &I : *BB) {
-      // Tokens can't be used in PHI nodes and live-out tokens prevent loop
-      // optimizations, so for the purposes of considered LCSSA form, we
-      // can ignore them.
-      if (I.getType()->isTokenTy())
-        continue;
+// Check that 'BB' doesn't have any uses outside of the 'L'
+static bool isBlockInLCSSAForm(const Loop &L, const BasicBlock &BB,
+                               DominatorTree &DT) {
+  for (const Instruction &I : BB) {
+    // Tokens can't be used in PHI nodes and live-out tokens prevent loop
+    // optimizations, so for the purposes of considered LCSSA form, we
+    // can ignore them.
+    if (I.getType()->isTokenTy())
+      continue;
 
-      for (Use &U : I.uses()) {
-        Instruction *UI = cast<Instruction>(U.getUser());
-        BasicBlock *UserBB = UI->getParent();
-        if (PHINode *P = dyn_cast<PHINode>(UI))
-          UserBB = P->getIncomingBlock(U);
-
-        // Check the current block, as a fast-path, before checking whether
-        // the use is anywhere in the loop.  Most values are used in the same
-        // block they are defined in.  Also, blocks not reachable from the
-        // entry are special; uses in them don't need to go through PHIs.
-        if (UserBB != BB &&
-            !contains(UserBB) &&
-            DT.isReachableFromEntry(UserBB))
-          return false;
-      }
+    for (const Use &U : I.uses()) {
+      const Instruction *UI = cast<Instruction>(U.getUser());
+      const BasicBlock *UserBB = UI->getParent();
+      if (const PHINode *P = dyn_cast<PHINode>(UI))
+        UserBB = P->getIncomingBlock(U);
+
+      // Check the current block, as a fast-path, before checking whether
+      // the use is anywhere in the loop.  Most values are used in the same
+      // block they are defined in.  Also, blocks not reachable from the
+      // entry are special; uses in them don't need to go through PHIs.
+      if (UserBB != &BB && !L.contains(UserBB) &&
+          DT.isReachableFromEntry(UserBB))
+        return false;
     }
   }
-
   return true;
 }
 
-bool Loop::isRecursivelyLCSSAForm(DominatorTree &DT) const {
-  if (!isLCSSAForm(DT))
-    return false;
-
-  return all_of(*this,
-                [&](const Loop *L) { return L->isRecursivelyLCSSAForm(DT); });
+bool Loop::isLCSSAForm(DominatorTree &DT) const {
+  // For each block we check that it doesn't have any uses outside of this loop.
+  return all_of(this->blocks(), [&](const BasicBlock *BB) {
+    return isBlockInLCSSAForm(*this, *BB, DT);
+  });
+}
+
+bool Loop::isRecursivelyLCSSAForm(DominatorTree &DT, const LoopInfo &LI) const {
+  // For each block we check that it doesn't have any uses outside of it's
+  // innermost loop. This process will transitivelly guarntee that current loop 
+  // and all of the nested loops are in the LCSSA form.
+  return all_of(this->blocks(), [&](const BasicBlock *BB) {
+    return isBlockInLCSSAForm(*LI.getLoopFor(BB), *BB, DT);
+  });
 }
 
 bool Loop::isLoopSimplifyForm() const {

llvm/lib/Transforms/Scalar/IndVarSimplify.cpp

@@ -505,7 +505,8 @@ Value *IndVarSimplify::expandSCEVIfNeeded(SCEVExpander &Rewriter, const SCEV *S,
 /// constant operands at the beginning of the loop.
 void IndVarSimplify::rewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter) {
   // Check a pre-condition.
-  assert(L->isRecursivelyLCSSAForm(*DT) && "Indvars did not preserve LCSSA!");
+  assert(L->isRecursivelyLCSSAForm(*DT, *LI) &&
+         "Indvars did not preserve LCSSA!");
 
   SmallVector<BasicBlock*, 8> ExitBlocks;
   L->getUniqueExitBlocks(ExitBlocks);
@@ -2184,7 +2185,8 @@ void IndVarSimplify::sinkUnusedInvariants(Loop *L) {
 
 bool IndVarSimplify::run(Loop *L) {
   // We need (and expect!) the incoming loop to be in LCSSA.
-  assert(L->isRecursivelyLCSSAForm(*DT) && "LCSSA required to run indvars!");
+  assert(L->isRecursivelyLCSSAForm(*DT, *LI) &&
+         "LCSSA required to run indvars!");
 
   // If LoopSimplify form is not available, stay out of trouble. Some notes:
   //  - LSR currently only supports LoopSimplify-form loops. Indvars'
@@ -2277,7 +2279,8 @@ bool IndVarSimplify::run(Loop *L) {
   Changed |= DeleteDeadPHIs(L->getHeader(), TLI);
 
   // Check a post-condition.
-  assert(L->isRecursivelyLCSSAForm(*DT) && "Indvars did not preserve LCSSA!");
+  assert(L->isRecursivelyLCSSAForm(*DT, *LI) &&
+         "Indvars did not preserve LCSSA!");
 
   // Verify that LFTR, and any other change have not interfered with SCEV's
   // ability to compute trip count.

llvm/lib/Transforms/Utils/LCSSA.cpp

@@ -323,7 +323,8 @@ struct LCSSAWrapperPass : public FunctionPass {
   bool runOnFunction(Function &F) override;
   void verifyAnalysis() const override {
     assert(
-        all_of(*LI, [&](Loop *L) { return L->isRecursivelyLCSSAForm(*DT); }) &&
+        all_of(*LI,
+               [&](Loop *L) { return L->isRecursivelyLCSSAForm(*DT, *LI); }) &&
         "LCSSA form is broken!");
   };
 

llvm/lib/Transforms/Utils/LoopSimplify.cpp

@@ -366,7 +366,7 @@ static Loop *separateNestedLoop(Loop *L, BasicBlock *Preheader,
     // already be a use of an LCSSA phi node.
     formLCSSA(*L, *DT, LI, SE);
 
-    assert(NewOuter->isRecursivelyLCSSAForm(*DT) &&
+    assert(NewOuter->isRecursivelyLCSSAForm(*DT, *LI) &&
            "LCSSA is broken after separating nested loops!");
   }
 
@@ -810,8 +810,8 @@ bool LoopSimplify::runOnFunction(Function &F) {
   if (PreserveLCSSA) {
     assert(DT && "DT not available.");
     assert(LI && "LI not available.");
-    bool InLCSSA =
-        all_of(*LI, [&](Loop *L) { return L->isRecursivelyLCSSAForm(*DT); });
+    bool InLCSSA = all_of(
+        *LI, [&](Loop *L) { return L->isRecursivelyLCSSAForm(*DT, *LI); });
     assert(InLCSSA && "Requested to preserve LCSSA, but it's already broken.");
   }
 #endif
@@ -822,8 +822,8 @@ bool LoopSimplify::runOnFunction(Function &F) {
 
 #ifndef NDEBUG
   if (PreserveLCSSA) {
-    bool InLCSSA =
-        all_of(*LI, [&](Loop *L) { return L->isRecursivelyLCSSAForm(*DT); });
+    bool InLCSSA = all_of(
+        *LI, [&](Loop *L) { return L->isRecursivelyLCSSAForm(*DT, *LI); });
     assert(InLCSSA && "LCSSA is broken after loop-simplify.");
   }
 #endif