[llvm-commits] [llvm] r72276 - in /llvm/trunk: include/llvm/CodeGen/Passes.h include/llvm/CodeGen/RuntimeLibcalls.h lib/CodeGen/CMakeLists.txt lib/CodeGen/DwarfEHPrepare.cpp lib/CodeGen/LLVMTargetMachine.cpp lib/CodeGen/SelectionDAG/FastISel.cpp

[Eli Friedman]

On Fri, May 22, 2009 at 1:36 PM, Duncan Sands <baldrick at free.fr> wrote:
> Note that it is currently rare for this pass to actually do
> anything.  And in fact it normally shouldn't do anything at
> all given the code coming out of llvm-gcc!  But it does fire
> a few times in the testsuite.  As far as I can see this is
> almost always due to the LoopStrengthReduce codegen pass
> introducing pointless loop preheader blocks which are landing
> pads and only contain a branch to another block.  This other
> block contains an eh.exception call.  So probably by tweaking
> LoopStrengthReduce a bit this can be avoided.

AFAIK, LoopStrengthReduce doesn't modify the CFG itself; it's probably
an effect of LoopSimplify.

-Eli