Tweak IVUsers' concept of "interesting" to exclude add recurrences

where the step value is an induction variable from an outer loop, to
avoid trouble trying to re-expand such expressions. This effectively
hides such expressions from indvars and lsr, which prevents them
from getting into trouble.

llvm-svn: 111317

1 files changed, 16 insertions, 12 deletions

diff --git a/llvm/lib/Analysis/IVUsers.cpp b/llvm/lib/Analysis/IVUsers.cpp
index bd43026015b..fd514336be8 100644
--- a/llvm/lib/Analysis/IVUsers.cpp
+++ b/llvm/lib/Analysis/IVUsers.cpp
@@ -38,27 +38,31 @@ Pass *llvm::createIVUsersPass() {
 /// isInteresting - Test whether the given expression is "interesting" when
 /// used by the given expression, within the context of analyzing the
 /// given loop.
-static bool isInteresting(const SCEV *S, const Instruction *I, const Loop *L) {
-  // Anything loop-invariant is interesting.
-  if (!isa<SCEVUnknown>(S) && S->isLoopInvariant(L))
-    return true;
-
+static bool isInteresting(const SCEV *S, const Instruction *I, const Loop *L,
+                          ScalarEvolution *SE) {
   // An addrec is interesting if it's affine or if it has an interesting start.
   if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
     // Keep things simple. Don't touch loop-variant strides.
     if (AR->getLoop() == L)
       return AR->isAffine() || !L->contains(I);
-    // Otherwise recurse to see if the start value is interesting.
-    return isInteresting(AR->getStart(), I, L);
+    // Otherwise recurse to see if the start value is interesting, and that
+    // the step value is not interesting, since we don't yet know how to
+    // do effective SCEV expansions for addrecs with interesting steps.
+    return isInteresting(AR->getStart(), I, L, SE) &&
+          !isInteresting(AR->getStepRecurrence(*SE), I, L, SE);
   }
 
-  // An add is interesting if any of its operands is.
+  // An add is interesting if exactly one of its operands is interesting.
   if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
+    bool AnyInterestingYet = false;
     for (SCEVAddExpr::op_iterator OI = Add->op_begin(), OE = Add->op_end();
          OI != OE; ++OI)
-      if (isInteresting(*OI, I, L))
-        return true;
-    return false;
+      if (isInteresting(*OI, I, L, SE)) {
+        if (AnyInterestingYet)
+          return false;
+        AnyInterestingYet = true;
+      }
+    return AnyInterestingYet;
   }
 
   // Nothing else is interesting here.
@@ -84,7 +88,7 @@ bool IVUsers::AddUsersIfInteresting(Instruction *I) {
 
   // If we've come to an uninteresting expression, stop the traversal and
   // call this a user.
-  if (!isInteresting(ISE, I, L))
+  if (!isInteresting(ISE, I, L, SE))
     return false;
 
   SmallPtrSet<Instruction *, 4> UniqueUsers;