From 2c966d209bd8c96cd767506d0e9f4b8445dcce38 Mon Sep 17 00:00:00 2001
From: Sam Parker <sam.parker@arm.com>
Date: Thu, 12 Apr 2018 12:49:40 +0000
Subject: [PATCH] [IRCE] isKnownNonNegative helper function

Created a helper function to query for non negative SCEVs. Uses the
SGE predicate to catch constants that could be interpreted as
negative.

Differential Revision: https://reviews.llvm.org/D45481

llvm-svn: 329907
---
 .../Scalar/InductiveRangeCheckElimination.cpp         | 11 +++++++++--
 test/Transforms/IRCE/variable-loop-bounds.ll          |  2 +-
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp b/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
index 330a2c234c3..8d9e9581ac7 100644
--- a/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
+++ b/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
@@ -804,6 +804,13 @@ static bool CannotBeMinInLoop(const SCEV *BoundSCEV, Loop *L,
                                      SE.getConstant(Min));
 }
 
+static bool isKnownNonNegativeInLoop(const SCEV *BoundSCEV, Loop *L,
+                                     ScalarEvolution &SE) {
+  const SCEV *Zero = SE.getZero(BoundSCEV->getType());
+  return SE.isAvailableAtLoopEntry(BoundSCEV, L) &&
+         SE.isLoopEntryGuardedByCond(L, ICmpInst::ICMP_SGE, BoundSCEV, Zero);
+}
+
 Optional<LoopStructure>
 LoopStructure::parseLoopStructure(ScalarEvolution &SE,
                                   BranchProbabilityInfo *BPI, Loop &L,
@@ -963,8 +970,8 @@ LoopStructure::parseLoopStructure(ScalarEvolution &SE,
         // If both parts are known non-negative, it is profitable to use
         // unsigned comparison in increasing loop. This allows us to make the
         // comparison check against "RightSCEV + 1" more optimistic.
-        if (SE.isKnownNonNegative(IndVarStart) &&
-            SE.isKnownNonNegative(RightSCEV))
+        if (isKnownNonNegativeInLoop(IndVarStart, &L, SE) &&
+            isKnownNonNegativeInLoop(RightSCEV, &L, SE))
           Pred = ICmpInst::ICMP_ULT;
         else
           Pred = ICmpInst::ICMP_SLT;
diff --git a/test/Transforms/IRCE/variable-loop-bounds.ll b/test/Transforms/IRCE/variable-loop-bounds.ll
index d5a57093b32..5749b2c2d41 100644
--- a/test/Transforms/IRCE/variable-loop-bounds.ll
+++ b/test/Transforms/IRCE/variable-loop-bounds.ll
@@ -55,7 +55,7 @@ for.inc:
 ; CHECK-LABEL: test_inc_ne
 ; CHECK: main.exit.selector:
 ; CHECK: [[PSEUDO_PHI:%[^ ]+]] = phi i32 [ %inc, %for.inc ]
-; CHECK: [[COND:%[^ ]+]] = icmp slt i32 [[PSEUDO_PHI]], %N
+; CHECK: [[COND:%[^ ]+]] = icmp ult i32 [[PSEUDO_PHI]], %N
 ; CHECK: br i1 [[COND]], label %main.pseudo.exit, label %for.cond.cleanup.loopexit
 define void @test_inc_ne(i32* nocapture %a, i32* nocapture readonly %b, i32* nocapture readonly %c, i32 %N) {
 entry: