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Auto merge of #69290 - wesleywiser:speed_up_ctfe_stress_4, r=RalfJung

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Check `RUSTC_CTFE_BACKTRACE` much less by generating fewer errors

Before this change, `get_size_and_align()`  calls `get_fn_alloc()` *a
lot* in CTFE heavy code. This previously returned an `Error` which would
check if `RUSTC_CTFE_BACKTRACE` was set on construction. Doing this
turned out to be a performance hotspot as @nnethercote discovered in
#68792.

This is an alternate take on that PR which resolves the performance
issue by generating *many* fewer errors. Previously, `ctfe-stress-4`
would generate over 5,000,000 errors each of which would check for the
presence of the environment variable. With these changes, that number is
reduced to 30.

r? @RalfJung
This commit is contained in:
bors 2020-02-21 06:43:40 +00:00
commit 01a8b5f26e
1 changed files with 6 additions and 6 deletions
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12
src/librustc_mir/interpret/memory.rs
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@ -560,7 +560,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
// # Function pointers
// (both global from `alloc_map` and local from `extra_fn_ptr_map`)
if let Ok(_) = self.get_fn_alloc(id) {
if let Some(_) = self.get_fn_alloc(id) {
return if let AllocCheck::Dereferenceable = liveness {
// The caller requested no function pointers.
throw_unsup!(DerefFunctionPointer)
@ -602,14 +602,14 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
}
}
fn get_fn_alloc(&self, id: AllocId) -> InterpResult<'tcx, FnVal<'tcx, M::ExtraFnVal>> {
fn get_fn_alloc(&self, id: AllocId) -> Option<FnVal<'tcx, M::ExtraFnVal>> {
trace!("reading fn ptr: {}", id);
if let Some(extra) = self.extra_fn_ptr_map.get(&id) {
Ok(FnVal::Other(*extra))
Some(FnVal::Other(*extra))
} else {
match self.tcx.alloc_map.lock().get(id) {
Some(GlobalAlloc::Function(instance)) => Ok(FnVal::Instance(instance)),
_ => throw_unsup!(ExecuteMemory),
Some(GlobalAlloc::Function(instance)) => Some(FnVal::Instance(instance)),
_ => None,
}
}
}
@ -622,7 +622,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
if ptr.offset.bytes() != 0 {
throw_unsup!(InvalidFunctionPointer)
}
self.get_fn_alloc(ptr.alloc_id)
self.get_fn_alloc(ptr.alloc_id).ok_or_else(|| err_unsup!(ExecuteMemory).into())
}
pub fn mark_immutable(&mut self, id: AllocId) -> InterpResult<'tcx> {