diff options
Diffstat (limited to 'src/pass.h')
| -rw-r--r-- | src/pass.h | 19 |
1 files changed, 19 insertions, 0 deletions
diff --git a/src/pass.h b/src/pass.h index 041b80321..623c1f971 100644 --- a/src/pass.h +++ b/src/pass.h @@ -145,6 +145,25 @@ struct PassOptions { // neither of those can happen (and it is undefined behavior if they do). // // TODO: deprecate and remove ignoreImplicitTraps. + // + // Since trapsNeverHappen assumes a trap is never reached, it can in principle + // remove code like this: + // + // (i32.store ..) + // (unreachable) + // + // The trap isn't reached, by assumption, and if we reach the store then we'd + // reach the trap, so we can assume that isn't reached either, and TNH can + // remove both. We do have a specific limitation here, however, which is that + // trapsNeverHappen cannot remove calls to *imports*. We assume that an import + // might do things we cannot understand, so we never eliminate it. For + // example, in LLVM output we might see this: + // + // (call $abort) ;; a noreturn import - the process is halted with an error + // (unreachable) + // + // That trap is never actually reached since the abort halts execution. In TNH + // we can remove the trap but not the call right before it. bool trapsNeverHappen = false; // Optimize assuming that the low 1K of memory is not valid memory for the // application to use. In that case, we can optimize load/store offsets in |