Handle code gen for the unreachable instruction if it's the only instruction in
the function. We'll just turn it into a "trap" instruction instead.
The problem with not handling this is that it might generate a prologue without
the equivalent epilogue to go with it:
$ cat t.ll
define void @foo() {
entry:
unreachable
}
$ llc -o - t.ll -relocation-model=pic -disable-fp-elim -unwind-tables
.section __TEXT,__text,regular,pure_instructions
.globl _foo
.align 4, 0x90
_foo: ## @foo
Leh_func_begin0:
## BB#0: ## %entry
pushq %rbp
Ltmp0:
movq %rsp, %rbp
Ltmp1:
Leh_func_end0:
...
The unwind tables then have bad data in them causing all sorts of problems.
Fixes <rdar://problem/8096481>.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@108473 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 458e865..1fa887c 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -796,6 +796,7 @@
#define HANDLE_INST(NUM, OPCODE, CLASS) \
case Instruction::OPCODE: visit##OPCODE((CLASS&)I); break;
#include "llvm/Instruction.def"
+#undef HANDLE_INST
}
// Assign the ordering to the freshly created DAG nodes.
@@ -2194,6 +2195,19 @@
getValue(I.getAddress())));
}
+void SelectionDAGBuilder::visitUnreachable(const UnreachableInst &I) {
+ // If the function consists of a single "unreachable" instruction, emit a
+ // "trap". This prevents the back-ends from generating empty functions or
+ // functions which have a prologue, but no epilogue.
+ const BasicBlock *BB = I.getParent();
+ const Function *F = BB->getParent();
+
+ if (F->size() == 1 && BB->size() == 1 &&
+ isa<UnreachableInst>(BB->getTerminator()))
+ DAG.setRoot(DAG.getNode(ISD::TRAP, getCurDebugLoc(),
+ MVT::Other, getRoot()));
+}
+
void SelectionDAGBuilder::visitFSub(const User &I) {
// -0.0 - X --> fneg
const Type *Ty = I.getType();
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h
index 46733d6..8621637 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h
@@ -385,7 +385,7 @@
void visitBr(const BranchInst &I);
void visitSwitch(const SwitchInst &I);
void visitIndirectBr(const IndirectBrInst &I);
- void visitUnreachable(const UnreachableInst &I) { /* noop */ }
+ void visitUnreachable(const UnreachableInst &I);
// Helpers for visitSwitch
bool handleSmallSwitchRange(CaseRec& CR,