[ConstraintElimination] Bail out if system gets too big.

For some inputs, the constraint system can grow quite large during
solving, because it replaces complex constraints with one or more
simpler constraints. This adds a cut-off to avoid compile-time explosion
on problematic inputs.

diff --git a/llvm/include/llvm/Analysis/ConstraintSystem.h b/llvm/include/llvm/Analysis/ConstraintSystem.h
index 2e55d5d..83c1fb4 100644 (file)
--- a/llvm/include/llvm/Analysis/ConstraintSystem.h
+++ b/llvm/include/llvm/Analysis/ConstraintSystem.h
@@ -79,6 +79,9 @@ public:
   bool isConditionImplied(SmallVector<int64_t, 8> R);
 
   void popLastConstraint() { Constraints.pop_back(); }
+
+  /// Returns the number of rows in the constraint system.
+  unsigned size() const { return Constraints.size(); }
 };
 } // namespace llvm
 

diff --git a/llvm/lib/Analysis/ConstraintSystem.cpp b/llvm/lib/Analysis/ConstraintSystem.cpp
index f3a2834..1d58280 100644 (file)
--- a/llvm/lib/Analysis/ConstraintSystem.cpp
+++ b/llvm/lib/Analysis/ConstraintSystem.cpp
@@ -84,6 +84,9 @@ bool ConstraintSystem::eliminateUsingFM() {
                      .getZExtValue();
       }
       NewSystem.push_back(std::move(NR));
+      // Give up if the new system gets too big.
+      if (NewSystem.size() > 500)
+        return false;
     }
   }
   Constraints = std::move(NewSystem);

diff --git a/llvm/test/Transforms/ConstraintElimination/large-system-growth.ll b/llvm/test/Transforms/ConstraintElimination/large-system-growth.ll
new file mode 100644 (file)
index 0000000..e2d603e
--- /dev/null
+++ b/llvm/test/Transforms/ConstraintElimination/large-system-growth.ll
@@ -0,0 +1,86 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -constraint-elimination -S %s | FileCheck %s
+
+; The system for the function below grows quite large. Check to make sure
+; we can handle that scenario.
+define void @test(i64 %x, i8* %y, i8* %z, i8* %w) {
+; CHECK-LABEL: @test(
+; CHECK-NEXT:    [[TMP22:%.*]] = getelementptr inbounds i8, i8* [[Y:%.*]], i64 [[X:%.*]]
+; CHECK-NEXT:    [[TMP26:%.*]] = icmp ult i8* [[TMP22]], [[Z:%.*]]
+; CHECK-NEXT:    br i1 [[TMP26]], label [[BB28:%.*]], label [[EARLY_EXIT:%.*]]
+; CHECK:       early.exit:
+; CHECK-NEXT:    unreachable
+; CHECK:       bb28:
+; CHECK-NEXT:    [[TMP29:%.*]] = getelementptr inbounds i8, i8* [[Y]], i64 [[X]]
+; CHECK-NEXT:    [[TMP30:%.*]] = icmp ult i8* [[TMP29]], [[Z]]
+; CHECK-NEXT:    br i1 true, label [[EARLY_EXIT]], label [[BB32:%.*]]
+; CHECK:       bb32:
+; CHECK-NEXT:    [[TMP33:%.*]] = icmp ult i8* [[TMP29]], [[Z]]
+; CHECK-NEXT:    br i1 true, label [[BB35:%.*]], label [[EARLY_EXIT]]
+; CHECK:       bb35:
+; CHECK-NEXT:    [[TMP36:%.*]] = icmp ult i8* [[Y]], [[Z]]
+; CHECK-NEXT:    br i1 true, label [[EARLY_EXIT]], label [[BB38:%.*]]
+; CHECK:       bb38:
+; CHECK-NEXT:    [[TMP41:%.*]] = icmp ult i8* [[Y]], [[Z]]
+; CHECK-NEXT:    br i1 true, label [[EARLY_EXIT]], label [[BB43:%.*]]
+; CHECK:       bb43:
+; CHECK-NEXT:    [[TMP47:%.*]] = getelementptr inbounds i8, i8* [[W:%.*]], i64 [[X]]
+; CHECK-NEXT:    [[TMP48:%.*]] = icmp ult i8* [[TMP47]], [[Y]]
+; CHECK-NEXT:    br i1 [[TMP48]], label [[EARLY_EXIT]], label [[BB50:%.*]]
+; CHECK:       bb50:
+; CHECK-NEXT:    [[TMP52:%.*]] = getelementptr inbounds i8, i8* [[W]], i64 [[X]]
+; CHECK-NEXT:    [[TMP53:%.*]] = icmp ult i8* [[TMP52]], [[Y]]
+; CHECK-NEXT:    br i1 true, label [[EARLY_EXIT]], label [[BB55:%.*]]
+; CHECK:       bb55:
+; CHECK-NEXT:    [[TMP57:%.*]] = icmp ult i8* [[W]], [[Y]]
+; CHECK-NEXT:    br i1 true, label [[BB59:%.*]], label [[EARLY_EXIT]]
+; CHECK:       bb59:
+; CHECK-NEXT:    [[TMP60:%.*]] = icmp ult i8* [[W]], [[Y]]
+; CHECK-NEXT:    call void @use(i1 true)
+; CHECK-NEXT:    ret void
+;
+  %tmp22 = getelementptr inbounds i8, i8* %y, i64 %x
+  %tmp26 = icmp ult i8* %tmp22, %z
+  br i1 %tmp26, label %bb28, label %early.exit
+
+early.exit:
+  unreachable
+
+bb28:
+  %tmp29 = getelementptr inbounds i8, i8* %y, i64 %x
+  %tmp30 = icmp ult i8* %tmp29, %z
+  br i1 %tmp30, label %early.exit, label %bb32
+
+bb32:
+  %tmp33 = icmp ult i8* %tmp29, %z
+  br i1 %tmp33, label %bb35, label %early.exit
+
+bb35:
+  %tmp36 = icmp ult i8* %y, %z
+  br i1 %tmp36, label %early.exit, label %bb38
+
+bb38:
+  %tmp41 = icmp ult i8* %y, %z
+  br i1 %tmp41, label %early.exit, label %bb43
+
+bb43:
+  %tmp47 = getelementptr inbounds i8, i8* %w, i64 %x
+  %tmp48 = icmp ult i8* %tmp47, %y
+  br i1 %tmp48, label %early.exit, label %bb50
+
+bb50:
+  %tmp52 = getelementptr inbounds i8, i8* %w, i64 %x
+  %tmp53 = icmp ult i8* %tmp52, %y
+  br i1 %tmp53, label %early.exit, label %bb55
+
+bb55:
+  %tmp57 = icmp ult i8* %w, %y
+  br i1 %tmp57, label %bb59, label %early.exit
+
+bb59:
+  %tmp60 = icmp ult i8* %w, %y
+  call void @use(i1 %tmp60)
+  ret void
+}
+
+declare void @use(i1)