[PATCH] D158776: [ConstraintElim] Handle trivial (ICMP_ULE, 0, B) in doesHold.

[Florian Hahn via Phabricator via llvm-commits]

fhahn created this revision.
fhahn added reviewers: zjaffal, nikic, rapidsna, antoniofrighetto.
Herald added subscribers: StephenFan, hiraditya.
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D152730 <https://reviews.llvm.org/D152730> may add trivial pre-conditions of the form (ICMP_ULE, 0, B),
which won't be handled automatically by the constraint system, because
we don't add Var >= 0 for all variables in the unsigned system.

Handling the trivial condition explicitly here avoids having the
increase the number of rows in the system per variable.

https://alive2.llvm.org/ce/z/QC92ur

Depends on D152730 <https://reviews.llvm.org/D152730>.

Fixes #63125.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D158776

Files:
  llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
  llvm/test/Transforms/ConstraintElimination/loops-header-tested-pointer-cmps.ll
  llvm/test/Transforms/ConstraintElimination/monotonic-int-phis.ll
  llvm/test/Transforms/PhaseOrdering/loop-access-checks.ll


Index: llvm/test/Transforms/PhaseOrdering/loop-access-checks.ll
===================================================================
--- llvm/test/Transforms/PhaseOrdering/loop-access-checks.ll
+++ llvm/test/Transforms/PhaseOrdering/loop-access-checks.ll
@@ -145,13 +145,7 @@
 ; CHECK:       for.cond.cleanup:
 ; CHECK-NEXT:    ret void
 ; CHECK:       for.body:
-; CHECK-NEXT:    [[I_010:%.*]] = phi i64 [ [[INC:%.*]], [[OPERATOR_ACC_EXIT:%.*]] ], [ 0, [[ENTRY:%.*]] ]
-; CHECK-NEXT:    [[CMP_NOT_I:%.*]] = icmp ugt i64 [[SUB_PTR_DIV_I_I]], [[I_010]]
-; CHECK-NEXT:    br i1 [[CMP_NOT_I]], label [[OPERATOR_ACC_EXIT]], label [[IF_THEN_I:%.*]]
-; CHECK:       if.then.i:
-; CHECK-NEXT:    tail call void @abort() #[[ATTR1:[0-9]+]]
-; CHECK-NEXT:    unreachable
-; CHECK:       operator_acc.exit:
+; CHECK-NEXT:    [[I_010:%.*]] = phi i64 [ [[INC:%.*]], [[FOR_BODY]] ], [ 0, [[ENTRY:%.*]] ]
 ; CHECK-NEXT:    [[ADD_PTR_I:%.*]] = getelementptr inbounds double, ptr [[TMP1]], i64 [[I_010]]
 ; CHECK-NEXT:    [[TMP2:%.*]] = load double, ptr [[ADD_PTR_I]], align 8
 ; CHECK-NEXT:    [[ADD:%.*]] = fadd double [[TMP2]], 1.000000e+00
Index: llvm/test/Transforms/ConstraintElimination/monotonic-int-phis.ll
===================================================================
--- llvm/test/Transforms/ConstraintElimination/monotonic-int-phis.ll
+++ llvm/test/Transforms/ConstraintElimination/monotonic-int-phis.ll
@@ -20,8 +20,7 @@
 ; CHECK-NEXT:    [[C:%.*]] = icmp eq i16 [[IV]], [[LEN]]
 ; CHECK-NEXT:    br i1 [[C]], label [[EXIT]], label [[FOR_BODY:%.*]]
 ; CHECK:       for.body:
-; CHECK-NEXT:    [[T_2:%.*]] = icmp ult i16 [[IV]], [[A]]
-; CHECK-NEXT:    [[AND:%.*]] = and i1 true, [[T_2]]
+; CHECK-NEXT:    [[AND:%.*]] = and i1 true, true
 ; CHECK-NEXT:    br i1 [[AND]], label [[LOOP_LATCH]], label [[EXIT]]
 ; CHECK:       loop.latch:
 ; CHECK-NEXT:    call void @use(i16 [[IV]])
Index: llvm/test/Transforms/ConstraintElimination/loops-header-tested-pointer-cmps.ll
===================================================================
--- llvm/test/Transforms/ConstraintElimination/loops-header-tested-pointer-cmps.ll
+++ llvm/test/Transforms/ConstraintElimination/loops-header-tested-pointer-cmps.ll
@@ -572,15 +572,12 @@
 ; CHECK-NEXT:    br i1 [[EXITCOND]], label [[FOR_BODY:%.*]], label [[FOR_END:%.*]]
 ; CHECK:       for.body:
 ; CHECK-NEXT:    [[GEP_IV:%.*]] = getelementptr inbounds i8, ptr [[PTR]], i16 [[IV]]
-; CHECK-NEXT:    [[CMP_IV_UPPER:%.*]] = icmp ule ptr [[UPPER]], [[GEP_IV]]
-; CHECK-NEXT:    [[OR:%.*]] = or i1 false, [[CMP_IV_UPPER]]
+; CHECK-NEXT:    [[OR:%.*]] = or i1 false, false
 ; CHECK-NEXT:    br i1 [[OR]], label [[TRAP]], label [[FOR_BODY_1:%.*]]
 ; CHECK:       for.body.1:
 ; CHECK-NEXT:    [[ADD:%.*]] = add nuw nsw i16 [[IV]], 1
 ; CHECK-NEXT:    [[GEP_IV_1:%.*]] = getelementptr inbounds i8, ptr [[PTR]], i16 [[ADD]]
-; CHECK-NEXT:    [[CMP_IV_1_LOWER:%.*]] = icmp ugt ptr [[LOWER]], [[GEP_IV_1]]
-; CHECK-NEXT:    [[CMP_IV_1_UPPER:%.*]] = icmp ule ptr [[UPPER]], [[GEP_IV_1]]
-; CHECK-NEXT:    [[OR_1:%.*]] = or i1 [[CMP_IV_1_LOWER]], [[CMP_IV_1_UPPER]]
+; CHECK-NEXT:    [[OR_1:%.*]] = or i1 false, false
 ; CHECK-NEXT:    br i1 [[OR_1]], label [[TRAP]], label [[FOR_LATCH]]
 ; CHECK:       for.latch:
 ; CHECK-NEXT:    store i8 0, ptr [[GEP_IV]], align 4
Index: llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
+++ llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
@@ -737,6 +737,8 @@
 
 bool ConstraintInfo::doesHold(CmpInst::Predicate Pred, Value *A,
                               Value *B) const {
+  if (Pred == CmpInst::ICMP_ULE && A == Constant::getNullValue(A->getType()))
+    return true;
   auto R = getConstraintForSolving(Pred, A, B);
   return R.isValid(*this) &&
          getCS(R.IsSigned).isConditionImplied(R.Coefficients);


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