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Auto merge of #129714 - saethlin:half-a-recursion, r=compiler-errors
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Use a reduced recursion limit in the MIR inliner's cycle breaker

This probably papers over #128887, but primarily I'm opening this PR because multiple compiler people have thought about making this change which probably means it's a good idea.

r? compiler-errors
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bors committed Aug 29, 2024
2 parents 6cf068d + 950437a commit 784d444
Showing 1 changed file with 9 additions and 1 deletion.
10 changes: 9 additions & 1 deletion compiler/rustc_mir_transform/src/inline/cycle.rs
Original file line number Diff line number Diff line change
Expand Up @@ -135,6 +135,14 @@ pub(crate) fn mir_callgraph_reachable<'tcx>(
}
false
}
// FIXME(-Znext-solver): Remove this hack when trait solver overflow can return an error.
// In code like that pointed out in #128887, the type complexity we ask the solver to deal with
// grows as we recurse into the call graph. If we use the same recursion limit here and in the
// solver, the solver hits the limit first and emits a fatal error. But if we use a reduced
// limit, we will hit the limit first and give up on looking for inlining. And in any case,
// the default recursion limits are quite generous for us. If we need to recurse 64 times
// into the call graph, we're probably not going to find any useful MIR inlining.
let recursion_limit = tcx.recursion_limit() / 2;
process(
tcx,
param_env,
Expand All @@ -143,7 +151,7 @@ pub(crate) fn mir_callgraph_reachable<'tcx>(
&mut Vec::new(),
&mut FxHashSet::default(),
&mut FxHashMap::default(),
tcx.recursion_limit(),
recursion_limit,
)
}

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