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[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.
This commit is contained in:
Florian Hahn 2020-12-06 19:58:33 +00:00
parent d1c14dd0fc
commit f19876c536
3 changed files with 92 additions and 0 deletions
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3
llvm/include/llvm/Analysis/ConstraintSystem.h
View File

@ -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

3
llvm/lib/Analysis/ConstraintSystem.cpp
View File

@ -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);

86
llvm/test/Transforms/ConstraintElimination/large-system-growth.ll Normal file
View File

@ -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)