Currently, the ASan executables built with -O0 are unnecessarily slow. The main reason is that ASan instrumentation pass inserts redundant checks around promotable allocas. These allocas do not get instrumented under -O1 because they get converted to virtual registered by mem2reg. With this patch, ASan instrumentation pass will only instrument non promotable allocas, giving us a speedup of 39% on a collection of benchmarks with -O0. (There is no measurable speedup at -O1.)
- We've initially discussed creating another pass to annotate the uninteresting load and stores. However, the check is simple and having a separate pass seems like an overkill.
- A bunch of ASan llvm tests are written using promotable allocas. I've added volatile stores or marked the existing stores as volatile to make the allocas non-promotable.
- Two of the runtime tests also seem to depend on being run with -O0. With this modification, I am getting the same behavior as when the tests are run with higher optimization levels. I've turned off the mode on those tests since I am not sure if a better fix is available. They fail on comparing values returned by __asan_region_is_poisoned.
- Should "isInterestingAlloca()" be hoisted out of "FunctionStackPoisoner" and used in "isInterestingMemoryAccess"?