[PATCH] D12950: [SCEV] Teach isLoopBackedgeGuardedByCond to exploit trip counts.

[hfinkel@anl.gov via llvm-commits]

hfinkel added inline comments.

================
Comment at: lib/Analysis/ScalarEvolution.cpp:7008
@@ -7007,1 +7007,3 @@
 
+  // See if we can exploit an already computed trip count to prove the
+  // predicate.
----------------
already computed => already-computed

================
Comment at: lib/Analysis/ScalarEvolution.cpp:7010
@@ +7009,3 @@
+  // predicate.
+  auto BECountIt = BackedgeTakenCounts.find(L);
+  if (BECountIt != BackedgeTakenCounts.end()) {
----------------
It seems like we should add a comment in ScalarEvolution.h somewhere that isLoopBackedgeGuardedByCond will potentially-return more-accurate answers if you compute the look trip count first.

This seems unfortunate, but I suppose we can't force the trip-count computation here because we might infinitely recurse?


================
Comment at: lib/Analysis/ScalarEvolution.cpp:7019
@@ +7018,3 @@
+      const SCEV *LoopCounter =
+          getAddRecExpr(getZero(Ty), getOne(Ty), L, SCEV::FlagAnyWrap);
+      if (isImpliedCond(Pred, LHS, RHS, ICmpInst::ICMP_ULT, LoopCounter,
----------------
Don't we know that SCEV::FlagNW | SCEV::FlagNUW here? Otherwise, it would not really be a trip count, would it?



http://reviews.llvm.org/D12950