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From 4c7e1defbddafcfcfe1211b041d43a36114a8f48 Mon Sep 17 00:00:00 2001
From: Valentin Churavy <v.churavy@gmail.com>
Date: Sat, 14 Dec 2019 10:33:30 -0500
Subject: [PATCH 2/2] [CodegenPrepare] Guard against degenerate branches
Summary:
Guard against a potential crash observed in https://github.com/JuliaLang/julia/issues/32994#issuecomment-524249628
If two branches are collapsed we can encounter a degenerate conditional branch `TBB==FBB`.
The subsequent code assumes that they differ, so we exit out early.
Reviewers: ributzka, spatel
Subscribers: loladiro, dexonsmith, hiraditya, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D66657
---
llvm/lib/CodeGen/CodeGenPrepare.cpp | 4 ++++
.../CodeGen/X86/codegen-prepare-collapse.ll | 18 ++++++++++++++++++
2 files changed, 22 insertions(+)
create mode 100644 llvm/test/CodeGen/X86/codegen-prepare-collapse.ll
diff --git a/lib/CodeGen/CodeGenPrepare.cpp b/lib/CodeGen/CodeGenPrepare.cpp
index c35f8666fa3..3647641c594 100644
--- a/lib/CodeGen/CodeGenPrepare.cpp
+++ b/lib/CodeGen/CodeGenPrepare.cpp
@@ -6929,6 +6929,10 @@ bool CodeGenPrepare::splitBranchCondition(Function &F) {
if (Br1->getMetadata(LLVMContext::MD_unpredictable))
continue;
+ // The merging of mostly empty BB can cause a degenerate branch.
+ if (TBB == FBB)
+ continue;
+
unsigned Opc;
Value *Cond1, *Cond2;
if (match(LogicOp, m_And(m_OneUse(m_Value(Cond1)),
diff --git a/test/CodeGen/X86/codegen-prepare-collapse.ll b/test/CodeGen/X86/codegen-prepare-collapse.ll
new file mode 100644
index 00000000000..18e3ef7afbd
--- /dev/null
+++ b/test/CodeGen/X86/codegen-prepare-collapse.ll
@@ -0,0 +1,18 @@
+; RUN: llc -fast-isel=true -O1 -mtriple=x86_64-unkown-linux-gnu -start-before=codegenprepare -stop-after=codegenprepare -o - < %s | FileCheck %s
+
+; CHECK-LABEL: @foo
+define void @foo() {
+top:
+; CHECK: br label %L34
+ br label %L34
+
+L34: ; preds = %L34, %L34, %top
+ %.sroa.075.0 = phi i64 [ undef, %top ], [ undef, %L34 ], [ undef, %L34 ]
+ %0 = icmp sgt i8 undef, -1
+ %cond5896 = icmp eq i8 0, 2
+ %cond58 = and i1 %cond5896, %0
+; During codegenprepare such degenerate branches can occur and should not
+; lead to crashes.
+; CHECK: br label %L34
+ br i1 %cond58, label %L34, label %L34
+}
--
2.24.1
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