If we have a function like this:
void bork() {
int *address = 0;
*address = 0;
}
It's compiled into LLVM code that looks like this:
define void @bork() noreturn nounwind {
entry:
unreachable
}
This is bad on some platforms (like PPC) because it will generate the label for
the function but no body. The label could end up being associated with some
non-code related stuff, like a section. This places a "trap" instruction if the
SimplifyCFG pass removed all code from the function leaving only one
"unreachable" instruction.
llvm-svn: 46387
diff --git a/llvm/lib/Transforms/Scalar/SimplifyCFG.cpp b/llvm/lib/Transforms/Scalar/SimplifyCFG.cpp
index 3d1a5be..9d0757a 100644
--- a/llvm/lib/Transforms/Scalar/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Scalar/SimplifyCFG.cpp
@@ -26,6 +26,7 @@
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Constants.h"
#include "llvm/Instructions.h"
+#include "llvm/Intrinsics.h"
#include "llvm/Module.h"
#include "llvm/ParameterAttributes.h"
#include "llvm/Support/CFG.h"
@@ -154,8 +155,20 @@
bool Changed = MarkAliveBlocks(F.begin(), Reachable);
// If there are unreachable blocks in the CFG...
- if (Reachable.size() == F.size())
+ if (Reachable.size() == F.size()) {
+ if (F.size() == 1) {
+ // If the function has only one block with an "unreachable" instruction,
+ // then we should create *some* code for it. Issue a "trap" instead.
+ BasicBlock &BB = F.front();
+
+ if (BB.size() == 1 && dyn_cast<UnreachableInst>(&BB.front()))
+ new CallInst(Intrinsic::getDeclaration(F.getParent(),
+ Intrinsic::trap),
+ "", &BB.front());
+ }
+
return Changed;
+ }
assert(Reachable.size() < F.size());
NumSimpl += F.size()-Reachable.size();
diff --git a/llvm/test/CFrontend/2008-01-25-EmptyFunction.c b/llvm/test/CFrontend/2008-01-25-EmptyFunction.c
new file mode 100644
index 0000000..896738e
--- /dev/null
+++ b/llvm/test/CFrontend/2008-01-25-EmptyFunction.c
@@ -0,0 +1,7 @@
+// RUN: %llvmgcc -O2 -S -o - -emit-llvm %s | grep llvm.trap
+// RUN: %llvmgcc -O2 -S -o - -emit-llvm %s | grep unreachable
+
+void bork() {
+ int *address = 0;
+ *address = 0;
+}