Author: void Date: Fri Jan 25 19:43:44 2008 New Revision: 46387 URL: http://llvm.org/viewvc/llvm-project?rev=46387&view=rev Log: 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. Added: llvm/trunk/test/CFrontend/2008-01-25-EmptyFunction.c Modified: llvm/trunk/lib/Transforms/Scalar/SimplifyCFG.cpp Modified: llvm/trunk/lib/Transforms/Scalar/SimplifyCFG.cpp URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/SimplifyCFG.cpp?rev=46387&r1=46386&r2=46387&view=diff ============================================================================== --- llvm/trunk/lib/Transforms/Scalar/SimplifyCFG.cpp (original) +++ llvm/trunk/lib/Transforms/Scalar/SimplifyCFG.cpp Fri Jan 25 19:43:44 2008 @@ -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(); Added: llvm/trunk/test/CFrontend/2008-01-25-EmptyFunction.c URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CFrontend/2008-01-25-EmptyFunction.c?rev=46387&view=auto ============================================================================== --- llvm/trunk/test/CFrontend/2008-01-25-EmptyFunction.c (added) +++ llvm/trunk/test/CFrontend/2008-01-25-EmptyFunction.c Fri Jan 25 19:43:44 2008 @@ -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; +} _______________________________________________ llvm-commits mailing list llvm-commits@cs.uiuc.edu http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits