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fix: apply range constraints to return values from unconstrained functions #4217

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merged 1 commit into from
Jan 31, 2024

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Description

Problem*

Resolves

Summary*

Consider the program

unconstrained fn identity(x: u8) -> u8 {
    x
}

fn main(x: u8, y: pub Field) {
    assert(identity(x) as Field == 1000);
}

From looking at the type information, this program should be unsatisfiable. A u8 should not be able to contain the value 1000 so the assertion should always fail. If we look at the generated ACIR however we see that the return value of identity() doesn't need to be a valid u8 and so can be set by the prover to be 1000.

BLACKBOX::RANGE [(_0, num_bits: 8)] [ ]
BRILLIG: inputs: [Single(Expression { mul_terms: [], linear_combinations: [(1, Witness(0))], q_c: 0 })]
outputs: [Simple(Witness(2))]
[Mov { destination: RegisterIndex(2), source: RegisterIndex(0) }, Const { destination: RegisterIndex(0), value: Value { inner: 0 } }, Const { destination: RegisterIndex(1), value: Value { inner: 0 } }, Mov { destination: RegisterIndex(2), source: RegisterIndex(2) }, Call { location: 7 }, Mov { destination: RegisterIndex(0), source: RegisterIndex(2) }, Stop, Mov { destination: RegisterIndex(3), source: RegisterIndex(2) }, Mov { destination: RegisterIndex(2), source: RegisterIndex(3) }, Return]

EXPR [ (1, _2) -1000 ]

This PR modifies ACIR gen so that when inserting a call to a brillig function, we apply range constraints to the return values to ensure that the results provided by the prover must be valid for those types.

Additional Context

Note that we cannot enforce safety for all types which have validity conditions outside of the type system. e.g. If an unconstrained function returns a U128 then this will not be constrained as its limbs are made up of Fields so no constraints will be applied allowing a potentially invalid value to be returned.

Documentation*

Check one:

  • No documentation needed.
  • Documentation included in this PR.
  • [Exceptional Case] Documentation to be submitted in a separate PR.

PR Checklist*

  • I have tested the changes locally.
  • I have formatted the changes with Prettier and/or cargo fmt on default settings.

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Changes to circuit sizes

Generated at commit: dfa5fe5f4e5cfabfb9a2680c2f2b3b08169fa626, compared to commit: 26e961860709e9c0ab3d1eb561fd39b5bd95a0fb

🧾 Summary (10% most significant diffs)

Program ACIR opcodes (+/-) % Circuit size (+/-) %
brillig_to_le_bytes +31 ❌ +3100.00% +84 ❌ +233.33%
brillig_to_be_bytes +31 ❌ +3100.00% +84 ❌ +233.33%

Full diff report 👇
Program ACIR opcodes (+/-) % Circuit size (+/-) %
brillig_to_le_bytes 32 (+31) +3100.00% 120 (+84) +233.33%
brillig_to_be_bytes 32 (+31) +3100.00% 120 (+84) +233.33%
brillig_sha256 97 (+32) +49.23% 162 (+40) +32.79%
brillig_blake2s 102 (+32) +45.71% 168 (+40) +31.25%
brillig_keccak 164 (+32) +24.24% 3,102 (+40) +1.31%
brillig_fns_as_values 32 (+5) +18.52% 3,476 (+9) +0.26%
databus 13 (+1) +8.33% 2,777 (+1) +0.04%

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Thanks for finding this!

@TomAFrench TomAFrench added this pull request to the merge queue Jan 31, 2024
@github-merge-queue github-merge-queue bot removed this pull request from the merge queue due to failed status checks Jan 31, 2024
@TomAFrench TomAFrench added this pull request to the merge queue Jan 31, 2024
Merged via the queue into master with commit 3af2a89 Jan 31, 2024
33 checks passed
@TomAFrench TomAFrench deleted the tf/apply-range-constraints-to-brillig-outputs branch January 31, 2024 15:05
TomAFrench added a commit that referenced this pull request Jan 31, 2024
* master:
  fix: apply range constraints to return values from unconstrained functions (#4217)
TomAFrench added a commit that referenced this pull request Feb 2, 2024
* master: (22 commits)
  feat: remove predicate from `sort` intrinsic function (#4228)
  chore: add test for missing lambda closure environment (#2120) (#4212)
  chore(docs): Updates following `is_recursive` flag removal (#4199)
  fix: from field with constant values (#4226)
  feat: Option expect method (#4219)
  feat: Evaluation of dynamic assert messages (#4101)
  chore(docs): XOR typo in docs (#4223)
  fix: apply range constraints to return values from unconstrained functions (#4217)
  fix(lsp): replace panics with errors (#4209)
  feat: Improve Error Handling for Cargo in Bootstrap Script (#4211)
  fix: prevent declarations of blackbox functions outside of the stdlib (#4177)
  feat: disable unused variable checks on low-level and oracle functions (#4179)
  chore: Rename acir_docs.md to README.md (#4208)
  feat: remove replacement of boolean range opcodes with `AssertZero` opcodes (#4107)
  chore(docs): updating docs to match new recursion interfacee (#4187)
  feat!: Sync commits from `aztec-packages` (#4144)
  feat: multiply first to allow more ACIR gen optimizations (#4201)
  feat: Move bounded_vec into the noir stdlib (#4197)
  chore: simplify marking black box function outputs as solvable (#4194)
  chore(doc): Add docs for `assert_max_bit_size` (#4196)
  ...
github-merge-queue bot pushed a commit that referenced this pull request Feb 12, 2024
🤖 I have created a release *beep* *boop*
---


<details><summary>0.24.0</summary>

## [0.24.0](v0.23.0...v0.24.0)
(2024-02-12)


### ⚠ BREAKING CHANGES

* rename bigint_neg into bigint_sub
(AztecProtocol/aztec-packages#4420)
* Add expression width into acir
(AztecProtocol/aztec-packages#4014)
* init storage macro
(AztecProtocol/aztec-packages#4200)
* **acir:** Move `is_recursive` flag to be part of the circuit
definition (AztecProtocol/aztec-packages#4221)
* Sync commits from `aztec-packages`
([#4144](#4144))

### Features

* Add bit size to const opcode
(AztecProtocol/aztec-packages#4385)
([158c8ce](158c8ce))
* Add brillig array index check
([#4127](#4127))
([c29f85f](c29f85f))
* Add definitions for From and Into traits to Noir prelude
([#4169](#4169))
([4421ce4](4421ce4))
* Add expression width into acir
(AztecProtocol/aztec-packages#4014)
([158c8ce](158c8ce))
* Add instrumentation for tracking variables in debugging
([#4122](#4122))
([c58d691](c58d691))
* Add option to print monomorphized program
([#4119](#4119))
([80f7e29](80f7e29))
* Add support for overriding expression width
([#4117](#4117))
([c8026d5](c8026d5))
* Add warnings for usage of restricted bit sizes
([#4234](#4234))
([0ffc38b](0ffc38b))
* Allow bitshifts to be represented in SSA for brillig
([#4301](#4301))
([d86ff1a](d86ff1a))
* Allow brillig to read arrays directly from memory
(AztecProtocol/aztec-packages#4460)
([158c8ce](158c8ce))
* Allow globals to refer to any expression
([#4293](#4293))
([479330e](479330e))
* Allow nested arrays and vectors in Brillig foreign calls
(AztecProtocol/aztec-packages#4478)
([158c8ce](158c8ce))
* Allow variables and stack trace inspection in the debugger
([#4184](#4184))
([bf263fc](bf263fc))
* **avm:** Back in avm context with macro - refactor context
(AztecProtocol/aztec-packages#4438)
([158c8ce](158c8ce))
* **aztec-nr:** Initial work for aztec public vm macro
(AztecProtocol/aztec-packages#4400)
([158c8ce](158c8ce))
* Deallocate stack items at the instruction level
([#4339](#4339))
([8f024a8](8f024a8))
* Disable constraint bubbling pass
([#4131](#4131))
([9ba2de6](9ba2de6))
* Disable unused variable checks on low-level and oracle functions
([#4179](#4179))
([8f70e57](8f70e57))
* Evaluation of dynamic assert messages
([#4101](#4101))
([c284e01](c284e01))
* Improve Error Handling for Cargo in Bootstrap Script
([#4211](#4211))
([3a90849](3a90849))
* Init storage macro
(AztecProtocol/aztec-packages#4200)
([158c8ce](158c8ce))
* **lsp:** Goto type reference for Struct
([#4091](#4091))
([d56cac2](d56cac2))
* Move bounded_vec into the noir stdlib
([#4197](#4197))
([c50621f](c50621f))
* Multiply first to allow more ACIR gen optimizations
([#4201](#4201))
([882639d](882639d))
* Option expect method
([#4219](#4219))
([8e042f2](8e042f2))
* Perform constraints on uncasted values if they are the same type
([#4303](#4303))
([816fa85](816fa85))
* Remove predicate from `sort` intrinsic function
([#4228](#4228))
([d646243](d646243))
* Remove replacement of boolean range opcodes with `AssertZero` opcodes
([#4107](#4107))
([dac0e87](dac0e87))
* Replace bitwise ANDs used for truncation with `Instruction::Truncate`
([#4327](#4327))
([eb67ff6](eb67ff6))
* Replace modulo operations with truncations where possible
([#4329](#4329))
([70f2435](70f2435))
* Separate compilation and expression narrowing in `nargo` interface
([#4100](#4100))
([62a4e37](62a4e37))
* Simplify all unsigned constant NOT instructions
([#4230](#4230))
([fab4a6e](fab4a6e))
* Sync commits from `aztec-packages`
([#4144](#4144))
([0205d3b](0205d3b))
* Use constraint information to perform constant folding
([#4060](#4060))
([9a4bf16](9a4bf16))


### Bug Fixes

* Accurate tracking of slice capacities across blocks
([#4240](#4240))
([7420dbb](7420dbb))
* Allow function calls in global definitions
([#4320](#4320))
([0dc205c](0dc205c))
* Allow performing bitwise NOT on unsigned integers
([#4229](#4229))
([b3ddf10](b3ddf10))
* Apply generic arguments from trait constraints before instantiating
identifiers ([#4121](#4121))
([eb6fc0f](eb6fc0f))
* Apply range constraints to return values from unconstrained functions
([#4217](#4217))
([3af2a89](3af2a89))
* Apply trait constraints from method calls
([#4152](#4152))
([68c5486](68c5486))
* Better errors for missing `fn` keyword
([#4154](#4154))
([057c208](057c208))
* Check for tests in all packages before failing due to an unsatisfied
test filter ([#4114](#4114))
([1107373](1107373))
* Clean error when attemping to return a slice from Brillig to ACIR
([#4280](#4280))
([bcad4ec](bcad4ec))
* Correct result when assigning shared arrays in unconstrained code
([#4210](#4210))
([bdd8a96](bdd8a96))
* **docs:** Codegen docs before cutting a new version
([#4183](#4183))
([2914310](2914310))
* Ensure that destination register is allocated when moving between
registers in brillig gen
([#4316](#4316))
([ca0a56e](ca0a56e))
* Ensure that unconstrained entrypoint functions don't generate
constraints ([#4292](#4292))
([fae4ead](fae4ead))
* From field with constant values
([#4226](#4226))
([593916b](593916b))
* **lsp:** Crash when file not in workspace
([#4146](#4146))
([cf7130f](cf7130f))
* **lsp:** Replace panics with errors
([#4209](#4209))
([26e9618](26e9618))
* Maintain correct type when simplifying `x ^ x`
([#4082](#4082))
([9d83c2b](9d83c2b))
* Message formatting for assert statement
([#4323](#4323))
([3972ead](3972ead))
* Prevent debugger crashing on circuits with no opcodes
([#4283](#4283))
([2e32845](2e32845))
* Prevent declarations of blackbox functions outside of the stdlib
([#4177](#4177))
([9fb6b09](9fb6b09))
* Remove panic from `init_log_level` in `acvm_js`
([#4195](#4195))
([2e26530](2e26530))
* Respect order in bubble up for redundant asserts
([#4109](#4109))
([189aa48](189aa48))
* Revert "correct result when assigning shared arrays" and added
regression test ([#4333](#4333))
([05e78b3](05e78b3))
* Save the data bus to the current function before generating others
([#4047](#4047))
([0a5bd4f](0a5bd4f))
* Simplify constant assert messages into `ConstrainError::Static`
([#4287](#4287))
([fd15052](fd15052))
* Ssa typing for array & slice indexes
([#4278](#4278))
([4074bab](4074bab))
* Ssa typing for assign_lvalue_index
([#4289](#4289))
([37f149c](37f149c))
* SSA typing for right shifts
([#4302](#4302))
([41ee1aa](41ee1aa))
* Ssa typing of make_offset
([#4277](#4277))
([e4378ee](e4378ee))
* Track graphs of item dependencies to find dependency cycles
([#4266](#4266))
([61eabf1](61eabf1))
* Type check ACIR mutable reference passed to brillig
([#4281](#4281))
([7e139de](7e139de))
* Update array method type signatures in the docs
([#4178](#4178))
([7c0a955](7c0a955))
* Zero out input to `to_radix` calls if inactive
([#4116](#4116))
([3f5bad3](3f5bad3))


### Miscellaneous Chores

* **acir:** Move `is_recursive` flag to be part of the circuit
definition (AztecProtocol/aztec-packages#4221)
([158c8ce](158c8ce))
* Rename bigint_neg into bigint_sub
(AztecProtocol/aztec-packages#4420)
([158c8ce](158c8ce))
</details>

<details><summary>0.40.0</summary>

## [0.40.0](v0.39.0...v0.40.0)
(2024-02-12)


### ⚠ BREAKING CHANGES

* rename bigint_neg into bigint_sub
(AztecProtocol/aztec-packages#4420)
* Add expression width into acir
(AztecProtocol/aztec-packages#4014)
* init storage macro
(AztecProtocol/aztec-packages#4200)
* **acir:** Move `is_recursive` flag to be part of the circuit
definition (AztecProtocol/aztec-packages#4221)
* Sync commits from `aztec-packages`
([#4144](#4144))
* Breaking changes from aztec-packages
([#3955](#3955))
* Rename Arithmetic opcode to AssertZero
([#3840](#3840))
* Remove unused methods on ACIR opcodes
([#3841](#3841))
* Remove partial backend feature
([#3805](#3805))

### Features

* Add bit size to const opcode
(AztecProtocol/aztec-packages#4385)
([158c8ce](158c8ce))
* Add expression width into acir
(AztecProtocol/aztec-packages#4014)
([158c8ce](158c8ce))
* Add instrumentation for tracking variables in debugging
([#4122](#4122))
([c58d691](c58d691))
* Add support for overriding expression width
([#4117](#4117))
([c8026d5](c8026d5))
* Allow brillig to read arrays directly from memory
(AztecProtocol/aztec-packages#4460)
([158c8ce](158c8ce))
* Allow nested arrays and vectors in Brillig foreign calls
(AztecProtocol/aztec-packages#4478)
([158c8ce](158c8ce))
* Allow variables and stack trace inspection in the debugger
([#4184](#4184))
([bf263fc](bf263fc))
* **avm:** Back in avm context with macro - refactor context
(AztecProtocol/aztec-packages#4438)
([158c8ce](158c8ce))
* **aztec-nr:** Initial work for aztec public vm macro
(AztecProtocol/aztec-packages#4400)
([158c8ce](158c8ce))
* Aztec-packages
([#3754](#3754))
([c043265](c043265))
* Breaking changes from aztec-packages
([#3955](#3955))
([5be049e](5be049e))
* Evaluation of dynamic assert messages
([#4101](#4101))
([c284e01](c284e01))
* Init storage macro
(AztecProtocol/aztec-packages#4200)
([158c8ce](158c8ce))
* Remove range constraints from witnesses which are constrained to be
constants ([#3928](#3928))
([afe9c7a](afe9c7a))
* Remove replacement of boolean range opcodes with `AssertZero` opcodes
([#4107](#4107))
([dac0e87](dac0e87))
* Speed up transformation of debug messages
([#3815](#3815))
([2a8af1e](2a8af1e))
* Sync `aztec-packages`
([#4011](#4011))
([fee2452](fee2452))
* Sync commits from `aztec-packages`
([#4068](#4068))
([7a8f3a3](7a8f3a3))
* Sync commits from `aztec-packages`
([#4144](#4144))
([0205d3b](0205d3b))


### Bug Fixes

* Deserialize odd length hex literals
([#3747](#3747))
([4000fb2](4000fb2))
* Remove panic from `init_log_level` in `acvm_js`
([#4195](#4195))
([2e26530](2e26530))
* Return error rather instead of panicking on invalid circuit
([#3976](#3976))
([67201bf](67201bf))


### Miscellaneous Chores

* **acir:** Move `is_recursive` flag to be part of the circuit
definition (AztecProtocol/aztec-packages#4221)
([158c8ce](158c8ce))
* Remove partial backend feature
([#3805](#3805))
([0383100](0383100))
* Remove unused methods on ACIR opcodes
([#3841](#3841))
([9e5d0e8](9e5d0e8))
* Rename Arithmetic opcode to AssertZero
([#3840](#3840))
([836f171](836f171))
* Rename bigint_neg into bigint_sub
(AztecProtocol/aztec-packages#4420)
([158c8ce](158c8ce))
</details>

---
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Please](https://github.com/googleapis/release-please). See
[documentation](https://github.com/googleapis/release-please#release-please).
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