validate promoteds

[RalfJung]

Turn on const-value validation for promoteds. This is made possible now that #67534 is resolved.

I don't think this is a breaking change. We don't promote any unsafe operation any more (since #77526 landed). We do promote const fn calls under some circumstances (in const/static initializers), but union field access and similar operations are not allowed in const fn. So now is a perfect time to add this check. :D

r? @oli-obk
Fixes #67465

[RalfJung]

Ah, but validation complains about...

error[E0080]: it is undefined behavior to use this value
  --> /home/r/src/rust/rustc/src/test/ui/consts/const-eval/promote-static.rs:7:1
   |
LL | / static NONE_REF_REF: &&Option<String> = {
LL | |     let x = &&NONE;
LL | |     x
LL | | };
   | |__^ type validation failed: encountered a reference pointing to a static variable at .<deref>
   |
   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.

Since promoteds are constants and constants may not point to statics.

[RalfJung]

Meanwhile, let's see if this affects perf.
@bors try @rust-timer queue

[rust-timer]

Awaiting bors try build completion.

[bors]

⌛ Trying commit 06ca7b7 with merge d24e527f2368bc3de48bd2932d21d8ced60d3318...

[rust-log-analyzer]

The job x86_64-gnu-llvm-9 failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

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---
failures:

---- [ui] ui/consts/const-eval/promote-static.rs stdout ----

error: test compilation failed although it shouldn't!
status: exit code: 1
command: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/src/test/ui/consts/const-eval/promote-static.rs" "-Zthreads=1" "--target=x86_64-unknown-linux-gnu" "--error-format" "json" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zemit-future-incompat-report" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/consts/const-eval/promote-static" "-A" "unused" "-Crpath" "-O" "-Cdebuginfo=0" "-Zunstable-options" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/consts/const-eval/promote-static/auxiliary"
------------------------------------------

------------------------------------------
stderr:
stderr:
------------------------------------------
error[E0080]: it is undefined behavior to use this value
  --> /checkout/src/test/ui/consts/const-eval/promote-static.rs:7:1
   |
LL | / static NONE_REF_REF: &&Option<String> = {
LL | |     let x = &&NONE;
LL | |     x
LL | | };
   | |__^ type validation failed: encountered a reference pointing to a static variable at .<deref>
   |
   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
error: aborting due to previous error

For more information about this error, try `rustc --explain E0080`.


------------------------------------------


---- [ui] ui/issues/issue-44373-2.rs stdout ----

error: test compilation failed although it shouldn't!
status: exit code: 1
command: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/src/test/ui/issues/issue-44373-2.rs" "-Zthreads=1" "--target=x86_64-unknown-linux-gnu" "--error-format" "json" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zemit-future-incompat-report" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/issues/issue-44373-2" "-A" "unused" "-Crpath" "-O" "-Cdebuginfo=0" "-Zunstable-options" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/issues/issue-44373-2/auxiliary"
------------------------------------------

------------------------------------------
stderr:
stderr:
------------------------------------------
error[E0080]: it is undefined behavior to use this value
  --> /checkout/src/test/ui/issues/issue-44373-2.rs:9:1
   |
LL | static CONTAINER: Container = Container(&[&FOO]);
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered a reference pointing to a static variable at .<deref>[0]
   |
   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
error: aborting due to previous error

For more information about this error, try `rustc --explain E0080`.

---

Some tests failed in compiletest suite=ui mode=ui host=x86_64-unknown-linux-gnu target=x86_64-unknown-linux-gnu


command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-tools-bin/compiletest" "--compile-lib-path" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/lib" "--run-lib-path" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/lib/rustlib/x86_64-unknown-linux-gnu/lib" "--rustc-path" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "--src-base" "/checkout/src/test/ui" "--build-base" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui" "--stage-id" "stage2-x86_64-unknown-linux-gnu" "--suite" "ui" "--mode" "ui" "--target" "x86_64-unknown-linux-gnu" "--host" "x86_64-unknown-linux-gnu" "--llvm-filecheck" "/usr/lib/llvm-9/bin/FileCheck" "--nodejs" "/usr/bin/node" "--host-rustcflags" "-Crpath -O -Cdebuginfo=0 -Zunstable-options  -Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "--target-rustcflags" "-Crpath -O -Cdebuginfo=0 -Zunstable-options  -Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "--docck-python" "/usr/bin/python2.7" "--lldb-python" "/usr/bin/python2.7" "--gdb" "/usr/bin/gdb" "--quiet" "--llvm-version" "9.0.0" "--llvm-components" "aarch64 aarch64asmparser aarch64codegen aarch64desc aarch64disassembler aarch64info aarch64utils aggressiveinstcombine all all-targets amdgpu amdgpuasmparser amdgpucodegen amdgpudesc amdgpudisassembler amdgpuinfo amdgpuutils analysis arm armasmparser armcodegen armdesc armdisassembler arminfo armutils asmparser asmprinter avr avrasmparser avrcodegen avrdesc avrdisassembler avrinfo binaryformat bitreader bitstreamreader bitwriter bpf bpfasmparser bpfcodegen bpfdesc bpfdisassembler bpfinfo codegen core coroutines coverage debuginfocodeview debuginfodwarf debuginfogsym debuginfomsf debuginfopdb demangle dlltooldriver engine executionengine fuzzmutate globalisel hexagon hexagonasmparser hexagoncodegen hexagondesc hexagondisassembler hexagoninfo instcombine instrumentation interpreter ipo irreader jitlink lanai lanaiasmparser lanaicodegen lanaidesc lanaidisassembler lanaiinfo libdriver lineeditor linker lto mc mca mcdisassembler mcjit mcparser mips mipsasmparser mipscodegen mipsdesc mipsdisassembler mipsinfo mirparser msp430 msp430asmparser msp430codegen msp430desc msp430disassembler msp430info native nativecodegen nvptx nvptxcodegen nvptxdesc nvptxinfo objcarcopts object objectyaml option orcjit passes perfjitevents powerpc powerpcasmparser powerpccodegen powerpcdesc powerpcdisassembler powerpcinfo profiledata remarks riscv riscvasmparser riscvcodegen riscvdesc riscvdisassembler riscvinfo riscvutils runtimedyld scalaropts selectiondag sparc sparcasmparser sparccodegen sparcdesc sparcdisassembler sparcinfo support symbolize systemz systemzasmparser systemzcodegen systemzdesc systemzdisassembler systemzinfo tablegen target textapi transformutils vectorize webassembly webassemblyasmparser webassemblycodegen webassemblydesc webassemblydisassembler webassemblyinfo windowsmanifest x86 x86asmparser x86codegen x86desc x86disassembler x86info x86utils xcore xcorecodegen xcoredesc xcoredisassembler xcoreinfo xray" "--system-llvm" "--cc" "" "--cxx" "" "--cflags" "" "--adb-path" "adb" "--adb-test-dir" "/data/tmp/work" "--android-cross-path" "" "--color" "always"


failed to run: /checkout/obj/build/bootstrap/debug/bootstrap --stage 2 test --exclude src/tools/tidy
Build completed unsuccessfully in 0:17:39

[bors]

☀️ Try build successful - checks-actions
Build commit: d24e527f2368bc3de48bd2932d21d8ced60d3318 (d24e527f2368bc3de48bd2932d21d8ced60d3318)

[rust-timer]

Queued d24e527f2368bc3de48bd2932d21d8ced60d3318 with parent 59aaa2a, future comparison URL.

@rustbot label: +S-waiting-on-perf

[oli-obk]

Since promoteds are constants and constants may not point to statics.

ah lol, I guess we need to differentiate between promoteds in statics and promoteds elsewhere?

[RalfJung]

I guess promoted in consts should not contain refs to statics, yeah...

[rust-timer]

Finished benchmarking try commit (d24e527f2368bc3de48bd2932d21d8ced60d3318): comparison url.

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. Please note that if the perf results are neutral, you should likely undo the rollup=never given below by specifying rollup- to bors.

Importantly, though, if the results of this run are non-neutral do not roll this PR up -- it will mask other regressions or improvements in the roll up.

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

[RalfJung]

Looks like there's a perf hit of up to 4.5% for some examples.

[RalfJung]

I fixed the breakage, tests should pass now (the ones I ran locally did).

What remains is deciding if we are okay with the perf hit.

[oli-obk]

So... I'm ok with this perf hit, though I'm wondering if we should somehow "turn it off" and just keep it as a sort of debug assertion that we aren't doing anything bad with promotion. I mean... this should never actually cause a validation failure afaict.

[RalfJung]

This would be true if we did not promote const fn calls in const/static bodies... at least on nightly, those can produce invalid results.

[oli-obk]

Riiight, those. So let's do this now and consider moving to debug assertions once we know the result of the crater run

@bors r+

[bors]

📌 Commit 97cae9c has been approved by oli-obk

[bors]

⌛ Testing commit 97cae9c with merge bb17823...

[bors]

☀️ Test successful - checks-actions
Approved by: oli-obk
Pushing bb17823 to master...