Fix normalization overflow ICEs in monomorphization #146096

adwinwhite · 2025-09-01T16:58:58Z

Fixes #92004
Fixes #92470
Fixes #95134
Fixes #105275
Fixes #105937
Fixes #117696-2
Fixes #118590
Fixes #122823
Fixes #131342
Fixes #139659

Analysis:

The causes of these issues are similar. They contain generic recursive functions that can be instantiated with different args infinitely at monomorphization stage.
Ideally this should be caught by the check_recursion_limit function. The reality is that normalization can reach recursion limit earlier than monomorphization's check because they calculate depths in different ways.
Since normalization is called everywhere, ICEs appear in different locations.

Fix:

If we abort on overflow with TypingMode::PostAnalysis in the trait solver, it would also catch these errors.
The main challenge is providing good diagnostics for them. So it's quite natural to put the check right before these normalization happening.
I first tried to check the whole MIR body's normalization and references_error. (As elaborate_drop handles normalization failure by returning ty::Error.)
It turns out that checking all Locals seems sufficient.
These types are gonna be normalized anyway. So with cache, these checks shouldn't be expensive.

This fixes these ICEs for both the next and old solver, though I'm not sure the change I made to the old solver is proper. Its overflow handling looks convoluted thus I didn't try to fix it more "upstream".

jieyouxu · 2025-09-02T09:55:13Z

@bors try @rust-timer queue

…ono1, r=<try> Fix normalization overflow ICEs in monomorphization

rust-bors · 2025-09-02T12:12:16Z

☀️ Try build successful (CI)
Build commit: fb35892 (fb35892cd06f475414cd254159fed42f93083db6, parent: 05abce5d058db0de3abd10f32f1a442d0f699b30)

rust-timer · 2025-09-02T13:22:45Z

Finished benchmarking commit (fb35892): comparison URL.

Overall result: ❌✅ regressions and improvements - please read the text below

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please do so in sufficient writing along with @rustbot label: +perf-regression-triaged. If not, please fix the regressions and do another perf run. If its results are neutral or positive, the label will be automatically removed.

@bors rollup=never
@rustbot label: -S-waiting-on-perf +perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	5.9%	[0.3%, 45.5%]	63
Regressions ❌ (secondary)	8.7%	[0.1%, 53.7%]	32
Improvements ✅ (primary)	-0.2%	[-0.3%, -0.1%]	21
Improvements ✅ (secondary)	-1.0%	[-2.9%, -0.1%]	28
All ❌✅ (primary)	4.4%	[-0.3%, 45.5%]	84

Max RSS (memory usage)

Results (primary 9.4%, secondary 6.5%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	9.4%	[1.2%, 31.2%]	57
Regressions ❌ (secondary)	6.5%	[1.4%, 19.0%]	31
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	9.4%	[1.2%, 31.2%]	57

Cycles

Results (primary 11.3%, secondary 16.9%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	11.3%	[1.7%, 51.8%]	44
Regressions ❌ (secondary)	19.5%	[2.5%, 64.2%]	15
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.8%	[-3.1%, -2.5%]	2
All ❌✅ (primary)	11.3%	[1.7%, 51.8%]	44

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 467.236s -> 465.852s (-0.30%)
Artifact size: 388.42 MiB -> 388.49 MiB (0.02%)

bjorn3 · 2025-09-04T06:57:18Z

tests/ui/codegen/normalization-overflow/recursion-issue-105937.rs

@@ -1,3 +1,4 @@
+//@ build-fail
 //@ known-bug: #105937


Suggested change

//@ known-bug: #105937

right? Same elsewhere.

adwinwhite · 2025-09-04T09:35:36Z

I have to make the check a query in order to cache its result for incremental build.
collect_and_partition_mono_items query is eval always. So optimzed_mir query in instance_mir and normalization query always got called. Even with query cache, loading MIR from disk is not that cheap.
That's why the regressions happened.

bors · 2025-09-09T19:31:26Z

☔ The latest upstream changes (presumably #145717) made this pull request unmergeable. Please resolve the merge conflicts.

saethlin · 2025-09-14T17:08:37Z

compiler/rustc_monomorphize/src/collector.rs

+// may be expensive.
+fn has_normalization_error_in_mono<'tcx>(tcx: TyCtxt<'tcx>, instance: Instance<'tcx>) -> bool {
+    let body = tcx.instance_mir(instance.def);
+    body.local_decls.iter().any(|local| {


Why are you instantiating types seen in local_decls instead of the entire body? I'm worried that an error will sneak by this check because it's hidden somewhere else in the MIR body.

I did check the whole body at first. Then I realized that instantiation is not cached and worried that the computational cost is too high if the body is huge, so I tried to scale down the check.

Ofc this is just speculation, I'm not sure about the real cost.

This is done in a query, which should provide the requisite level of caching. Switch this to check the whole body and I can submit another perf run before merging.

saethlin · 2025-09-14T17:10:45Z

Just one question ^ then I think this is good

cjgillot · 2025-09-14T17:58:17Z

compiler/rustc_monomorphize/src/collector.rs

+            if tcx.has_normalization_error_in_mono(instance) {
+                let def_id = instance.def_id();
+                let def_span = tcx.def_span(def_id);
+                let def_path_str = tcx.def_path_str(def_id);
+                tcx.dcx().emit_fatal(RecursionLimit {
+                    span: starting_item.span,
+                    instance,
+                    def_span,
+                    def_path_str,
+                });
+            }


Should we move error reporting to the query itself, and make the query return unit?

If we do so, the query would be dependent on starting_item.span which may pollute the cache unnecessarily?

rustbot · 2025-09-15T04:15:06Z

This PR was rebased onto a different master commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

adwinwhite · 2025-09-16T03:08:08Z

Ready for another perf run. :⁠-⁠)

saethlin · 2025-09-16T03:54:29Z

@bors try @rust-timer queue

…ono1, r=<try> Fix normalization overflow ICEs in monomorphization

rust-bors · 2025-09-16T06:03:34Z

☀️ Try build successful (CI)
Build commit: 3ce4b4f (3ce4b4f6df15e7de71a8b7125c2480f73f4c9a83, parent: 9d82de19dfae60e55c291f5f28e28cfc2c1b9630)

rust-timer · 2025-09-16T07:24:27Z

Finished benchmarking commit (3ce4b4f): comparison URL.

Overall result: ❌ regressions - please read the text below

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please do so in sufficient writing along with @rustbot label: +perf-regression-triaged. If not, please fix the regressions and do another perf run. If its results are neutral or positive, the label will be automatically removed.

@bors rollup=never
@rustbot label: -S-waiting-on-perf +perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	0.7%	[0.2%, 2.0%]	44
Regressions ❌ (secondary)	1.6%	[0.3%, 18.6%]	22
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.5%	[-0.5%, -0.5%]	1
All ❌✅ (primary)	0.7%	[0.2%, 2.0%]	44

Max RSS (memory usage)

Results (primary 0.8%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	1.4%	[0.7%, 2.1%]	5
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.0%	[-2.0%, -2.0%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.8%	[-2.0%, 2.1%]	6

Cycles

Results (primary 2.6%, secondary 4.3%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	2.6%	[2.0%, 3.2%]	3
Regressions ❌ (secondary)	9.2%	[2.6%, 16.6%]	3
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.0%	[-3.9%, -2.2%]	2
All ❌✅ (primary)	2.6%	[2.0%, 3.2%]	3

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 475.305s -> 474.801s (-0.11%)
Artifact size: 390.12 MiB -> 390.20 MiB (0.02%)

rustbot assigned jieyouxu Sep 1, 2025

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rust-bors bot added a commit that referenced this pull request Sep 2, 2025

Auto merge of #146096 - adwinwhite:handle_normalization_overflow_in_m…

fb35892

…ono1, r=<try> Fix normalization overflow ICEs in monomorphization

rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Sep 2, 2025

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rustbot added perf-regression Performance regression. and removed S-waiting-on-perf Status: Waiting on a perf run to be completed. labels Sep 2, 2025

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adwinwhite force-pushed the handle_normalization_overflow_in_mono1 branch from 2e360ea to a454317 Compare September 15, 2025 04:15

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adwinwhite added 2 commits September 15, 2025 13:19

check normalization overflow in monomorphization

147b20e

propagate overflow error outside for the old solver

3030ed3

move crash tests to ui

ade5b67

adwinwhite force-pushed the handle_normalization_overflow_in_mono1 branch from a454317 to ade5b67 Compare September 15, 2025 05:20

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move a new crash test to ui, fixed by checking the whole body

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rust-bors bot added a commit that referenced this pull request Sep 16, 2025

Auto merge of #146096 - adwinwhite:handle_normalization_overflow_in_m…

3ce4b4f

…ono1, r=<try> Fix normalization overflow ICEs in monomorphization

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Fix normalization overflow ICEs in monomorphization #146096

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Fix normalization overflow ICEs in monomorphization #146096

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Analysis:

Fix:

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rust-timer commented Sep 2, 2025

Overall result: ❌✅ regressions and improvements - please read the text below

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Overall result: ❌ regressions - please read the text below

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adwinwhite commented Sep 1, 2025 •

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