[llvm] 16fde88 - [SCEV] Support unsigned predicates in isKnownPredicateViaNoOverflow

[Max Kazantsev via llvm-commits]

Author: Max Kazantsev
Date: 2020-09-22T17:14:05+07:00
New Revision: 16fde88dbd797b01f3c236062fbec50fe5bbf81d

URL: https://github.com/llvm/llvm-project/commit/16fde88dbd797b01f3c236062fbec50fe5bbf81d
DIFF: https://github.com/llvm/llvm-project/commit/16fde88dbd797b01f3c236062fbec50fe5bbf81d.diff

LOG: [SCEV] Support unsigned predicates in isKnownPredicateViaNoOverflow

SCEV should be able to prove facts like `x <u x+1<nuw>`.

Differential Revision: https://reviews.llvm.org/D88015
Reviewed By: lebedev.ri

Added: 
    

Modified: 
    llvm/lib/Analysis/ScalarEvolution.cpp
    llvm/unittests/Analysis/ScalarEvolutionTest.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 3bf7f2036136..39bccecd678c 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -9314,6 +9314,24 @@ bool ScalarEvolution::isKnownPredicateViaNoOverflow(ICmpInst::Predicate Pred,
     if (MatchBinaryAddToConst(LHS, RHS, C, SCEV::FlagNSW) && C.isNegative())
       return true;
     break;
+
+  case ICmpInst::ICMP_UGE:
+    std::swap(LHS, RHS);
+    LLVM_FALLTHROUGH;
+  case ICmpInst::ICMP_ULE:
+    // X u<= (X + C)<nuw> for any C
+    if (MatchBinaryAddToConst(RHS, LHS, C, SCEV::FlagNUW))
+      return true;
+    break;
+
+  case ICmpInst::ICMP_UGT:
+    std::swap(LHS, RHS);
+    LLVM_FALLTHROUGH;
+  case ICmpInst::ICMP_ULT:
+    // X u< (X + C)<nuw> if C != 0
+    if (MatchBinaryAddToConst(RHS, LHS, C, SCEV::FlagNUW) && !C.isNullValue())
+      return true;
+    break;
   }
 
   return false;

diff  --git a/llvm/unittests/Analysis/ScalarEvolutionTest.cpp b/llvm/unittests/Analysis/ScalarEvolutionTest.cpp
index 156427f56ead..04aaae18be27 100644
--- a/llvm/unittests/Analysis/ScalarEvolutionTest.cpp
+++ b/llvm/unittests/Analysis/ScalarEvolutionTest.cpp
@@ -1165,4 +1165,25 @@ TEST_F(ScalarEvolutionsTest, SCEVrewriteUnknowns) {
               cast<SCEVAddRecExpr>(ScevIV)->getStepRecurrence(SE));
   });
 }
+
+TEST_F(ScalarEvolutionsTest, SCEVAddNUW) {
+  LLVMContext C;
+  SMDiagnostic Err;
+  std::unique_ptr<Module> M = parseAssemblyString("define void @foo(i32 %x) { "
+                                                  "  ret void "
+                                                  "} ",
+                                                  Err, C);
+
+  ASSERT_TRUE(M && "Could not parse module?");
+  ASSERT_TRUE(!verifyModule(*M) && "Must have been well formed!");
+
+  runWithSE(*M, "foo", [](Function &F, LoopInfo &LI, ScalarEvolution &SE) {
+    auto *X = SE.getSCEV(getArgByName(F, "x"));
+    auto *One = SE.getOne(X->getType());
+    auto *Sum = SE.getAddExpr(X, One, SCEV::FlagNUW);
+    EXPECT_TRUE(SE.isKnownPredicate(ICmpInst::ICMP_UGE, Sum, X));
+    EXPECT_TRUE(SE.isKnownPredicate(ICmpInst::ICMP_UGT, Sum, X));
+  });
+}
+
 }  // end namespace llvm