[Loop Predication] Teach LP about reverse loops with uge and sge latch conditions

Add support of uge and sge latch condition to Loop Prediction for
reverse loops.

Reviewers: apilipenko, mkazantsev, sanjoy, anna
Reviewed By: anna
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D42837

llvm-svn: 324589

1 files changed, 8 insertions, 5 deletions

diff --git a/llvm/lib/Transforms/Scalar/LoopPredication.cpp b/llvm/lib/Transforms/Scalar/LoopPredication.cpp
index d1832f29e4f..69b3d0b7d73 100644
--- a/llvm/lib/Transforms/Scalar/LoopPredication.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopPredication.cpp
@@ -155,7 +155,7 @@
 // When S = -1 (i.e. reverse iterating loop), the transformation is supported
 // when:
 //   * The loop has a single latch with the condition of the form:
-//     B(X) = X <pred> latchLimit, where <pred> is u> or s>.
+//     B(X) = X <pred> latchLimit, where <pred> is u>, u>=, s>, or s>=.
 //   * The guard condition is of the form
 //     G(X) = X - 1 u< guardLimit
 //
@@ -171,6 +171,10 @@
 //     guardStart u< guardLimit && latchLimit u>= 1.
 //   Similarly for sgt condition the widened condition is:
 //     guardStart u< guardLimit && latchLimit s>= 1.
+//   For uge condition the widened condition is:
+//     guardStart u< guardLimit && latchLimit u> 1.
+//   For sge condition the widened condition is:
+//     guardStart u< guardLimit && latchLimit s> 1.
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Transforms/Scalar/LoopPredication.h"
@@ -485,9 +489,7 @@ Optional<Value *> LoopPredication::widenICmpRangeCheckDecrementingLoop(
   // latchLimit <pred> 1.
   // See the header comment for reasoning of the checks.
   Instruction *InsertAt = Preheader->getTerminator();
-  auto LimitCheckPred = ICmpInst::isSigned(LatchCheck.Pred)
-                            ? ICmpInst::ICMP_SGE
-                            : ICmpInst::ICMP_UGE;
+  auto LimitCheckPred = getLatchPredicateForGuard(LatchCheck.Pred);
   auto *FirstIterationCheck = expandCheck(Expander, Builder, ICmpInst::ICMP_ULT,
                                           GuardStart, GuardLimit, InsertAt);
   auto *LimitCheck = expandCheck(Expander, Builder, LimitCheckPred, LatchLimit,
@@ -671,7 +673,8 @@ Optional<LoopPredication::LoopICmp> LoopPredication::parseLoopLatchICmp() {
              Pred != ICmpInst::ICMP_ULE && Pred != ICmpInst::ICMP_SLE;
     } else {
       assert(Step->isAllOnesValue() && "Step should be -1!");
-      return Pred != ICmpInst::ICMP_UGT && Pred != ICmpInst::ICMP_SGT;
+      return Pred != ICmpInst::ICMP_UGT && Pred != ICmpInst::ICMP_SGT &&
+             Pred != ICmpInst::ICMP_UGE && Pred != ICmpInst::ICMP_SGE;
     }
   };