[llvm] 911a541 - [LazyValueInfo] Insert an Overdefined placeholder to prevent infinite recursion
Peilin Guo via llvm-commits
llvm-commits at lists.llvm.org
Fri May 7 01:07:05 PDT 2021
Author: Peilin Guo
Date: 2021-05-07T16:05:50+08:00
New Revision: 911a541620bcc78e637589b8623d94b8f3cdafba
URL: https://github.com/llvm/llvm-project/commit/911a541620bcc78e637589b8623d94b8f3cdafba
DIFF: https://github.com/llvm/llvm-project/commit/911a541620bcc78e637589b8623d94b8f3cdafba.diff
LOG: [LazyValueInfo] Insert an Overdefined placeholder to prevent infinite recursion
getValueFromCondition() uses a Visited set to record the intermediate value.
However, it uses a postorder way to compute the value first and update the
Visited set later. Thus it will be trapped into an infinite recursion if there
exists IRs that use no dominated by its def as in this example:
%tmp3 = or i1 undef, %tmp4
%tmp4 = or i1 undef, %tmp3
To prevent this, we can insert an Overdefined placeholder into the set
before computing the actual value.
Reviewed by: nikic
Differential Revision: https://reviews.llvm.org/D101273
Added:
llvm/test/Transforms/JumpThreading/insert-placeholder-to-prevent-infinite-recursion.ll
Modified:
llvm/lib/Analysis/LazyValueInfo.cpp
Removed:
################################################################################
diff --git a/llvm/lib/Analysis/LazyValueInfo.cpp b/llvm/lib/Analysis/LazyValueInfo.cpp
index 104f0e4b785dd..ea332148ceee2 100644
--- a/llvm/lib/Analysis/LazyValueInfo.cpp
+++ b/llvm/lib/Analysis/LazyValueInfo.cpp
@@ -1175,13 +1175,6 @@ getValueFromConditionImpl(Value *Val, Value *Cond, bool isTrueDest,
else
return ValueLatticeElement::getOverdefined();
- // Prevent infinite recursion if Cond references itself as in this example:
- // Cond: "%tmp4 = and i1 %tmp4, undef"
- // BL: "%tmp4 = and i1 %tmp4, undef"
- // BR: "i1 undef"
- if (L == Cond || R == Cond)
- return ValueLatticeElement::getOverdefined();
-
// if (L && R) -> intersect L and R
// if (!(L || R)) -> intersect L and R
// if (L || R) -> union L and R
@@ -1201,9 +1194,14 @@ getValueFromConditionImpl(Value *Val, Value *Cond, bool isTrueDest,
static ValueLatticeElement
getValueFromCondition(Value *Val, Value *Cond, bool isTrueDest,
SmallDenseMap<Value*, ValueLatticeElement> &Visited) {
- auto I = Visited.find(Cond);
- if (I != Visited.end())
- return I->second;
+ // Insert an Overdefined placeholder into the set to prevent
+ // infinite recursion if there exists IRs that use not
+ // dominated by its def as in this example:
+ // "%tmp3 = or i1 undef, %tmp4"
+ // "%tmp4 = or i1 undef, %tmp3"
+ auto Iter = Visited.try_emplace(Cond, ValueLatticeElement::getOverdefined());
+ if (!Iter.second)
+ return Iter.first->getSecond();
auto Result = getValueFromConditionImpl(Val, Cond, isTrueDest, Visited);
Visited[Cond] = Result;
diff --git a/llvm/test/Transforms/JumpThreading/insert-placeholder-to-prevent-infinite-recursion.ll b/llvm/test/Transforms/JumpThreading/insert-placeholder-to-prevent-infinite-recursion.ll
new file mode 100644
index 0000000000000..23a689f15b145
--- /dev/null
+++ b/llvm/test/Transforms/JumpThreading/insert-placeholder-to-prevent-infinite-recursion.ll
@@ -0,0 +1,80 @@
+; RUN: opt -jump-threading -S < %s | FileCheck %s
+ at a = common dso_local local_unnamed_addr global i16 0, align 2
+
+; Function Attrs: nofree norecurse nounwind
+define internal fastcc void @s() unnamed_addr {
+; CHECK-LABEL: @s(
+; CHECK-NEXT: for.cond1.preheader.lr.ph:
+; CHECK-NEXT: br label [[FOR_COND1_PREHEADER:%.*]]
+; CHECK: for.cond1.preheader:
+; CHECK-NEXT: [[DOTPR_I_19:%.*]] = phi i32 [ undef, [[FOR_COND1_PREHEADER_LR_PH:%.*]] ], [ 0, [[FOR_INC_SPLIT_1:%.*]] ]
+; CHECK-NEXT: [[TMP0:%.*]] = phi i16 [ undef, [[FOR_COND1_PREHEADER_LR_PH]] ], [ [[INC9:%.*]], [[FOR_INC_SPLIT_1]] ]
+; CHECK-NEXT: [[TOBOOL4_I:%.*]] = icmp eq i32 [[DOTPR_I_19]], 0
+; CHECK-NEXT: br i1 [[TOBOOL4_I]], label [[FOR_INC_SPLIT_1]], label [[FOR_BODY_LR_PH_I:%.*]]
+; CHECK: for.body.lr.ph.i:
+; CHECK-NEXT: ret void
+; CHECK: for.cond.for.end10_crit_edge:
+; CHECK-NEXT: ret void
+; CHECK: for.inc.split.1:
+; CHECK-NEXT: [[INC9]] = add i16 [[TMP0]], 1
+; CHECK-NEXT: [[TOBOOL:%.*]] = icmp eq i16 [[INC9]], 0
+; CHECK-NEXT: br i1 [[TOBOOL]], label [[FOR_COND_FOR_END10_CRIT_EDGE:%.*]], label [[FOR_COND1_PREHEADER]]
+;
+for.cond1.preheader.lr.ph:
+ br label %for.cond1.preheader
+
+for.cond1.preheader: ; preds = %for.inc.split.1, %for.cond1.preheader.lr.ph
+ %.pr.i.19 = phi i32 [ undef, %for.cond1.preheader.lr.ph ], [ 0, %for.inc.split.1 ]
+ %0 = phi i16 [ undef, %for.cond1.preheader.lr.ph ], [ %inc9, %for.inc.split.1 ]
+ %tobool4.i = icmp eq i32 %.pr.i.19, 0
+ br i1 %tobool4.i, label %t.exit, label %for.body.lr.ph.i
+
+for.body.lr.ph.i: ; preds = %for.cond1.preheader
+ ret void
+
+t.exit: ; preds = %for.cond1.preheader
+ br label %for.inc.split
+
+for.inc.split: ; preds = %t.exit
+ %tobool4.i.1 = icmp eq i32 %.pr.i.19, 0
+ br i1 %tobool4.i.1, label %for.inc.split.1, label %for.body.lr.ph.i.1
+
+for.cond.for.end10_crit_edge: ; preds = %for.inc.split.1
+ ret void
+
+for.body.lr.ph.i.1: ; preds = %for.inc.split
+ br label %for.body.lr.ph.split.i.1
+
+for.body.lr.ph.split.i.1: ; preds = %for.body.lr.ph.i.1
+ br label %for.body.preheader.i.1
+
+for.body.preheader.i.1: ; preds = %for.body.lr.ph.split.i.1
+ br label %for.body.i.us.1.preheader
+
+for.body.i.us.1.preheader: ; preds = %for.body.preheader.i.1
+ br label %for.body.i.us.1
+
+for.body.i.us.1: ; preds = %lor.end.i.us.1, %for.body.i.us.1.preheader
+ %.b.i.us.1 = phi i1 [ %spec.select44.i.us.1, %lor.end.i.us.1 ], [ undef, %for.body.i.us.1.preheader ]
+ br i1 %.b.i.us.1, label %lor.end.i.us.1, label %lor.rhs.i.us.1
+
+lor.rhs.i.us.1: ; preds = %for.body.i.us.1
+ %conv5.i.us.1 = trunc i32 undef to i8
+ br label %lor.end.i.us.1
+
+lor.end.i.us.1: ; preds = %lor.rhs.i.us.1, %for.body.i.us.1
+ %.b31.i.us.1 = or i1 undef, %.b.i.us.1
+ %spec.select44.i.us.1 = or i1 undef, %.b31.i.us.1
+ br i1 undef, label %for.end18.loopexit42.i.1.loopexit, label %for.body.i.us.1
+
+for.end18.loopexit42.i.1.loopexit: ; preds = %lor.end.i.us.1
+ br label %for.end18.loopexit42.i.1
+
+for.end18.loopexit42.i.1: ; preds = %for.end18.loopexit42.i.1.loopexit
+ br label %for.inc.split.1
+
+for.inc.split.1: ; preds = %for.end18.loopexit42.i.1, %for.inc.split
+ %inc9 = add i16 %0, 1
+ %tobool = icmp eq i16 %inc9, 0
+ br i1 %tobool, label %for.cond.for.end10_crit_edge, label %for.cond1.preheader
+}
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