[X86] Fix a crash in FEntryInserter Pass.
Summary:
FEntryInserter pass unconditionally derefs the first Instruction
in the first Basic Block. The pass crashes when the first
BasicBlock is empty. Fix the crash by not dereferencing the basic
Block iterator. This fixes an issue observed when building Linux kernel
4.4 with clang.
Fixes PR33971.
Reviewers: hfinkel, niravd, dblaikie
Reviewed By: niravd
Subscribers: davide, llvm-commits
Differential Revision: https://reviews.llvm.org/D35979
llvm-svn: 309694
diff --git a/llvm/lib/CodeGen/FEntryInserter.cpp b/llvm/lib/CodeGen/FEntryInserter.cpp
index 0759bf6..9781338 100644
--- a/llvm/lib/CodeGen/FEntryInserter.cpp
+++ b/llvm/lib/CodeGen/FEntryInserter.cpp
@@ -41,10 +41,8 @@
return false;
auto &FirstMBB = *MF.begin();
- auto &FirstMI = *FirstMBB.begin();
-
auto *TII = MF.getSubtarget().getInstrInfo();
- BuildMI(FirstMBB, FirstMI, FirstMI.getDebugLoc(),
+ BuildMI(FirstMBB, FirstMBB.begin(), DebugLoc(),
TII->get(TargetOpcode::FENTRY_CALL));
return true;
}