1 files changed, 34 insertions, 16 deletions
diff --git a/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp b/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
index 5519a00c12c9..d8d7acae5c9f 100644
--- a/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
+++ b/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -31,8 +31,8 @@
 #include "llvm/ADT/None.h"
 #include "llvm/ADT/Optional.h"
 #include "llvm/ADT/STLExtras.h"
-#include "llvm/ADT/SmallSet.h"
 #include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/SmallSet.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/ADT/iterator_range.h"
@@ -44,7 +44,6 @@
 #include "llvm/Analysis/TargetLibraryInfo.h"
 #include "llvm/Analysis/TargetTransformInfo.h"
 #include "llvm/Analysis/ValueTracking.h"
-#include "llvm/Transforms/Utils/Local.h"
 #include "llvm/IR/BasicBlock.h"
 #include "llvm/IR/Constant.h"
 #include "llvm/IR/ConstantRange.h"
@@ -68,6 +67,7 @@
 #include "llvm/IR/User.h"
 #include "llvm/IR/Value.h"
 #include "llvm/IR/ValueHandle.h"
+#include "llvm/InitializePasses.h"
 #include "llvm/Pass.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/CommandLine.h"
@@ -79,6 +79,7 @@
 #include "llvm/Transforms/Scalar.h"
 #include "llvm/Transforms/Scalar/LoopPassManager.h"
 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
+#include "llvm/Transforms/Utils/Local.h"
 #include "llvm/Transforms/Utils/LoopUtils.h"
 #include "llvm/Transforms/Utils/SimplifyIndVar.h"
 #include <cassert>
@@ -125,10 +126,9 @@ DisableLFTR("disable-lftr", cl::Hidden, cl::init(false),
             cl::desc("Disable Linear Function Test Replace optimization"));
 
 static cl::opt<bool>
-LoopPredication("indvars-predicate-loops", cl::Hidden, cl::init(false),
+LoopPredication("indvars-predicate-loops", cl::Hidden, cl::init(true),
                 cl::desc("Predicate conditions in read only loops"));
 
-
 namespace {
 
 struct RewritePhi;
@@ -2663,11 +2663,11 @@ static const SCEV* getMaxBackedgeTakenCount(ScalarEvolution &SE,
   // merge the max and exact information to approximate a version of
   // getConstantMaxBackedgeTakenCount which isn't restricted to just constants.
   SmallVector<const SCEV*, 4> ExitCounts;
-  const SCEV *MaxConstEC = SE.getConstantMaxBackedgeTakenCount(L);
-  if (!isa<SCEVCouldNotCompute>(MaxConstEC))
-    ExitCounts.push_back(MaxConstEC);
   for (BasicBlock *ExitingBB : ExitingBlocks) {
     const SCEV *ExitCount = SE.getExitCount(L, ExitingBB);
+    if (isa<SCEVCouldNotCompute>(ExitCount))
+      ExitCount = SE.getExitCount(L, ExitingBB,
+                                  ScalarEvolution::ConstantMaximum);
     if (!isa<SCEVCouldNotCompute>(ExitCount)) {
       assert(DT.dominates(ExitingBB, L->getLoopLatch()) &&
              "We should only have known counts for exiting blocks that "
@@ -2835,6 +2835,10 @@ bool IndVarSimplify::predicateLoopExits(Loop *L, SCEVExpander &Rewriter) {
       !isSafeToExpand(ExactBTC, *SE))
     return Changed;
 
+  // If we end up with a pointer exit count, bail.  It may be unsized.
+  if (!ExactBTC->getType()->isIntegerTy())
+    return Changed;
+
   auto BadExit = [&](BasicBlock *ExitingBB) {
     // If our exiting block exits multiple loops, we can only rewrite the
     // innermost one.  Otherwise, we're changing how many times the innermost
@@ -2865,6 +2869,10 @@ bool IndVarSimplify::predicateLoopExits(Loop *L, SCEVExpander &Rewriter) {
         !isSafeToExpand(ExitCount, *SE))
       return true;
 
+    // If we end up with a pointer exit count, bail.  It may be unsized.
+    if (!ExitCount->getType()->isIntegerTy())
+      return true;
+
     return false;
   };
 
@@ -2936,7 +2944,7 @@ bool IndVarSimplify::predicateLoopExits(Loop *L, SCEVExpander &Rewriter) {
   //    varying check.
   Rewriter.setInsertPoint(L->getLoopPreheader()->getTerminator());
   IRBuilder<> B(L->getLoopPreheader()->getTerminator());
-  Value *ExactBTCV = nullptr; //lazy generated if needed
+  Value *ExactBTCV = nullptr; // Lazily generated if needed.
   for (BasicBlock *ExitingBB : ExitingBlocks) {
     const SCEV *ExitCount = SE->getExitCount(L, ExitingBB);
 
@@ -2991,15 +2999,15 @@ bool IndVarSimplify::run(Loop *L) {
   if (!L->isLoopSimplifyForm())
     return false;
 
-  // If there are any floating-point recurrences, attempt to
-  // transform them to use integer recurrences.
-  Changed |= rewriteNonIntegerIVs(L);
-
 #ifndef NDEBUG
   // Used below for a consistency check only
   const SCEV *BackedgeTakenCount = SE->getBackedgeTakenCount(L);
 #endif
 
+  // If there are any floating-point recurrences, attempt to
+  // transform them to use integer recurrences.
+  Changed |= rewriteNonIntegerIVs(L);
+
   // Create a rewriter object which we'll use to transform the code with.
   SCEVExpander Rewriter(*SE, DL, "indvars");
 #ifndef NDEBUG
@@ -3026,11 +3034,19 @@ bool IndVarSimplify::run(Loop *L) {
   NumElimIV += Rewriter.replaceCongruentIVs(L, DT, DeadInsts);
 
   // Try to eliminate loop exits based on analyzeable exit counts
-  Changed |= optimizeLoopExits(L, Rewriter);
+  if (optimizeLoopExits(L, Rewriter))  {
+    Changed = true;
+    // Given we've changed exit counts, notify SCEV
+    SE->forgetLoop(L);
+  }
   
   // Try to form loop invariant tests for loop exits by changing how many
   // iterations of the loop run when that is unobservable.
-  Changed |= predicateLoopExits(L, Rewriter);
+  if (predicateLoopExits(L, Rewriter)) {
+    Changed = true;
+    // Given we've changed exit counts, notify SCEV
+    SE->forgetLoop(L);
+  }
 
   // If we have a trip count expression, rewrite the loop's exit condition
   // using it.  
@@ -3118,7 +3134,8 @@ bool IndVarSimplify::run(Loop *L) {
          "Indvars did not preserve LCSSA!");
 
   // Verify that LFTR, and any other change have not interfered with SCEV's
-  // ability to compute trip count.
+  // ability to compute trip count.  We may have *changed* the exit count, but
+  // only by reducing it.
 #ifndef NDEBUG
   if (VerifyIndvars && !isa<SCEVCouldNotCompute>(BackedgeTakenCount)) {
     SE->forgetLoop(L);
@@ -3130,7 +3147,8 @@ bool IndVarSimplify::run(Loop *L) {
     else
       BackedgeTakenCount = SE->getTruncateOrNoop(BackedgeTakenCount,
                                                  NewBECount->getType());
-    assert(BackedgeTakenCount == NewBECount && "indvars must preserve SCEV");
+    assert(!SE->isKnownPredicate(ICmpInst::ICMP_ULT, BackedgeTakenCount,
+                                 NewBECount) && "indvars must preserve SCEV");
   }
 #endif