[PATCH] D88015: [SCEV] Support unsigned predicates in isKnownPredicateViaNoOverflow

[Max Kazantsev via Phabricator via llvm-commits]

mkazantsev created this revision.
mkazantsev added reviewers: fhahn, sanjoy, lebedev.ri, reames.
Herald added subscribers: llvm-commits, javed.absar, hiraditya.
Herald added a project: LLVM.
mkazantsev requested review of this revision.

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


https://reviews.llvm.org/D88015

Files:
  llvm/lib/Analysis/ScalarEvolution.cpp
  llvm/test/Transforms/IndVarSimplify/monotonic_checks.ll


Index: llvm/test/Transforms/IndVarSimplify/monotonic_checks.ll
===================================================================
--- llvm/test/Transforms/IndVarSimplify/monotonic_checks.ll
+++ llvm/test/Transforms/IndVarSimplify/monotonic_checks.ll
@@ -170,8 +170,7 @@
 ; CHECK:       loop:
 ; CHECK-NEXT:    [[IV:%.*]] = phi i32 [ [[LEN]], [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[BACKEDGE:%.*]] ]
 ; CHECK-NEXT:    [[IV_NEXT]] = add nuw nsw i32 [[IV]], 1
-; CHECK-NEXT:    [[RC:%.*]] = icmp ugt i32 [[IV_NEXT]], [[LEN]]
-; CHECK-NEXT:    br i1 [[RC]], label [[BACKEDGE]], label [[FAIL:%.*]]
+; CHECK-NEXT:    br i1 true, label [[BACKEDGE]], label [[FAIL:%.*]]
 ; CHECK:       backedge:
 ; CHECK-NEXT:    [[LOOP_COND:%.*]] = icmp ne i32 [[IV]], 1000
 ; CHECK-NEXT:    br i1 [[LOOP_COND]], label [[LOOP]], label [[EXIT:%.*]]
Index: llvm/lib/Analysis/ScalarEvolution.cpp
===================================================================
--- llvm/lib/Analysis/ScalarEvolution.cpp
+++ llvm/lib/Analysis/ScalarEvolution.cpp
@@ -9294,6 +9294,24 @@
     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;


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