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Extend GVN to perform local value numbering. #143333

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Extend GVN to perform local value numbering. #143333

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8216f59
Only decide once whether to use a complex projection.
cjgillot Sep 7, 2025
ce21b6b
Simplify project.
cjgillot Aug 24, 2025
a7bc0fc
Preemptively invalidate derefs when entering a bb.
cjgillot Oct 8, 2025
6ca1f4c
Extend GVN to perform local value numbering.
cjgillot Jun 23, 2025
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384 changes: 244 additions & 140 deletions compiler/rustc_mir_transform/src/gvn.rs
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4 changes: 4 additions & 0 deletions compiler/rustc_mir_transform/src/ssa.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -99,19 +99,23 @@ impl SsaLocals {
ssa
}

#[inline]
pub(super) fn num_locals(&self) -> usize {
self.assignments.len()
}

#[inline]
pub(super) fn locals(&self) -> impl Iterator<Item = Local> {
self.assignments.indices()
}

#[inline]
pub(super) fn is_ssa(&self, local: Local) -> bool {
matches!(self.assignments[local], Set1::One(_))
}

/// Return the number of uses if a local that are not "Deref".
#[inline]
pub(super) fn num_direct_uses(&self, local: Local) -> u32 {
self.direct_uses[local]
}
Expand Down
56 changes: 26 additions & 30 deletions tests/coverage/closure.cov-map
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Original file line number Diff line number Diff line change
Expand Up @@ -74,24 +74,22 @@ Number of file 0 mappings: 66
- Code(Counter(0)) at (prev + 1, 1) to (start + 0, 2)
Highest counter ID seen: c1

Function name: closure::main::{closure#0}
Raw bytes (51): 0x[01, 01, 01, 01, 05, 09, 01, 28, 05, 00, 06, 01, 01, 0d, 00, 1a, 01, 00, 1d, 00, 1e, 01, 01, 0c, 00, 14, 05, 00, 15, 02, 0a, 02, 02, 09, 00, 0a, 01, 01, 09, 00, 17, 01, 00, 18, 00, 20, 01, 01, 05, 00, 06]
Function name: closure::main::{closure#0} (unused)
Raw bytes (49): 0x[01, 01, 00, 09, 00, 28, 05, 00, 06, 00, 01, 0d, 00, 1a, 00, 00, 1d, 00, 1e, 00, 01, 0c, 00, 14, 00, 00, 15, 02, 0a, 00, 02, 09, 00, 0a, 00, 01, 09, 00, 17, 00, 00, 18, 00, 20, 00, 01, 05, 00, 06]
Number of files: 1
- file 0 => $DIR/closure.rs
Number of expressions: 1
- expression 0 operands: lhs = Counter(0), rhs = Counter(1)
Number of expressions: 0
Number of file 0 mappings: 9
- Code(Counter(0)) at (prev + 40, 5) to (start + 0, 6)
- Code(Counter(0)) at (prev + 1, 13) to (start + 0, 26)
- Code(Counter(0)) at (prev + 0, 29) to (start + 0, 30)
- Code(Counter(0)) at (prev + 1, 12) to (start + 0, 20)
- Code(Counter(1)) at (prev + 0, 21) to (start + 2, 10)
- Code(Expression(0, Sub)) at (prev + 2, 9) to (start + 0, 10)
= (c0 - c1)
- Code(Counter(0)) at (prev + 1, 9) to (start + 0, 23)
- Code(Counter(0)) at (prev + 0, 24) to (start + 0, 32)
- Code(Counter(0)) at (prev + 1, 5) to (start + 0, 6)
Highest counter ID seen: c1
- Code(Zero) at (prev + 40, 5) to (start + 0, 6)
- Code(Zero) at (prev + 1, 13) to (start + 0, 26)
- Code(Zero) at (prev + 0, 29) to (start + 0, 30)
- Code(Zero) at (prev + 1, 12) to (start + 0, 20)
- Code(Zero) at (prev + 0, 21) to (start + 2, 10)
- Code(Zero) at (prev + 2, 9) to (start + 0, 10)
- Code(Zero) at (prev + 1, 9) to (start + 0, 23)
- Code(Zero) at (prev + 0, 24) to (start + 0, 32)
- Code(Zero) at (prev + 1, 5) to (start + 0, 6)
Highest counter ID seen: (none)

Function name: closure::main::{closure#10} (unused)
Raw bytes (25): 0x[01, 01, 00, 04, 00, 9b, 01, 07, 00, 08, 00, 00, 09, 00, 11, 00, 00, 12, 00, 1e, 00, 00, 20, 00, 21]
Expand Down Expand Up @@ -199,24 +197,22 @@ Number of file 0 mappings: 7
- Code(Counter(0)) at (prev + 2, 9) to (start + 0, 10)
Highest counter ID seen: c1

Function name: closure::main::{closure#18}
Raw bytes (51): 0x[01, 01, 01, 01, 05, 09, 01, 19, 0d, 00, 0e, 01, 01, 15, 00, 22, 01, 00, 25, 00, 26, 01, 01, 14, 00, 1c, 05, 00, 1d, 02, 12, 02, 02, 11, 00, 12, 01, 01, 11, 00, 1f, 01, 00, 20, 00, 28, 01, 01, 0d, 00, 0e]
Function name: closure::main::{closure#18} (unused)
Raw bytes (49): 0x[01, 01, 00, 09, 00, 19, 0d, 00, 0e, 00, 01, 15, 00, 22, 00, 00, 25, 00, 26, 00, 01, 14, 00, 1c, 00, 00, 1d, 02, 12, 00, 02, 11, 00, 12, 00, 01, 11, 00, 1f, 00, 00, 20, 00, 28, 00, 01, 0d, 00, 0e]
Number of files: 1
- file 0 => $DIR/closure.rs
Number of expressions: 1
- expression 0 operands: lhs = Counter(0), rhs = Counter(1)
Number of expressions: 0
Number of file 0 mappings: 9
- Code(Counter(0)) at (prev + 25, 13) to (start + 0, 14)
- Code(Counter(0)) at (prev + 1, 21) to (start + 0, 34)
- Code(Counter(0)) at (prev + 0, 37) to (start + 0, 38)
- Code(Counter(0)) at (prev + 1, 20) to (start + 0, 28)
- Code(Counter(1)) at (prev + 0, 29) to (start + 2, 18)
- Code(Expression(0, Sub)) at (prev + 2, 17) to (start + 0, 18)
= (c0 - c1)
- Code(Counter(0)) at (prev + 1, 17) to (start + 0, 31)
- Code(Counter(0)) at (prev + 0, 32) to (start + 0, 40)
- Code(Counter(0)) at (prev + 1, 13) to (start + 0, 14)
Highest counter ID seen: c1
- Code(Zero) at (prev + 25, 13) to (start + 0, 14)
- Code(Zero) at (prev + 1, 21) to (start + 0, 34)
- Code(Zero) at (prev + 0, 37) to (start + 0, 38)
- Code(Zero) at (prev + 1, 20) to (start + 0, 28)
- Code(Zero) at (prev + 0, 29) to (start + 2, 18)
- Code(Zero) at (prev + 2, 17) to (start + 0, 18)
- Code(Zero) at (prev + 1, 17) to (start + 0, 31)
- Code(Zero) at (prev + 0, 32) to (start + 0, 40)
- Code(Zero) at (prev + 1, 13) to (start + 0, 14)
Highest counter ID seen: (none)

Function name: closure::main::{closure#19}
Raw bytes (51): 0x[01, 01, 01, 01, 05, 09, 01, 43, 0d, 00, 0e, 01, 01, 15, 00, 22, 01, 00, 25, 00, 26, 01, 01, 14, 00, 1c, 05, 00, 1d, 02, 12, 02, 02, 11, 00, 12, 01, 01, 11, 00, 1f, 01, 00, 20, 00, 28, 01, 01, 0d, 00, 0e]
Expand Down
54 changes: 54 additions & 0 deletions tests/mir-opt/const_prop/borrowed_variable.borrow.GVN.diff
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Original file line number Diff line number Diff line change
@@ -0,0 +1,54 @@
- // MIR for `borrow` before GVN
+ // MIR for `borrow` after GVN

fn borrow() -> () {
let mut _0: ();
let mut _1: i32;
let _2: ();
let mut _3: i32;
let _5: ();
let mut _6: i32;
scope 1 {
debug x => _1;
let _4: &i32;
scope 2 {
debug r => _4;
}
}

bb0: {
- StorageLive(_1);
+ nop;
_1 = const 42_i32;
StorageLive(_2);
StorageLive(_3);
- _3 = copy _1;
- _2 = opaque::<i32>(move _3) -> [return: bb1, unwind unreachable];
+ _3 = const 42_i32;
+ _2 = opaque::<i32>(const 42_i32) -> [return: bb1, unwind unreachable];
}

bb1: {
StorageDead(_3);
StorageDead(_2);
StorageLive(_4);
_4 = &_1;
StorageLive(_5);
StorageLive(_6);
- _6 = copy _1;
- _5 = opaque::<i32>(move _6) -> [return: bb2, unwind unreachable];
+ _6 = const 42_i32;
+ _5 = opaque::<i32>(const 42_i32) -> [return: bb2, unwind unreachable];
}

bb2: {
StorageDead(_6);
StorageDead(_5);
_0 = const ();
StorageDead(_4);
- StorageDead(_1);
+ nop;
return;
}
}

50 changes: 50 additions & 0 deletions tests/mir-opt/const_prop/borrowed_variable.constptr.GVN.diff
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Original file line number Diff line number Diff line change
@@ -0,0 +1,50 @@
- // MIR for `constptr` before GVN
+ // MIR for `constptr` after GVN

fn constptr() -> () {
let mut _0: ();
let mut _1: i32;
let _2: ();
let mut _3: i32;
let _5: ();
let mut _6: i32;
scope 1 {
debug x => _1;
let _4: *const i32;
scope 2 {
debug r => _4;
}
}

bb0: {
StorageLive(_1);
_1 = const 42_i32;
StorageLive(_2);
StorageLive(_3);
- _3 = copy _1;
- _2 = opaque::<i32>(move _3) -> [return: bb1, unwind unreachable];
+ _3 = const 42_i32;
+ _2 = opaque::<i32>(const 42_i32) -> [return: bb1, unwind unreachable];
}

bb1: {
StorageDead(_3);
StorageDead(_2);
StorageLive(_4);
_4 = &raw const _1;
StorageLive(_5);
StorageLive(_6);
_6 = copy _1;
_5 = opaque::<i32>(move _6) -> [return: bb2, unwind unreachable];
}

bb2: {
StorageDead(_6);
StorageDead(_5);
_0 = const ();
StorageDead(_4);
StorageDead(_1);
return;
}
}

50 changes: 50 additions & 0 deletions tests/mir-opt/const_prop/borrowed_variable.mutborrow.GVN.diff
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Original file line number Diff line number Diff line change
@@ -0,0 +1,50 @@
- // MIR for `mutborrow` before GVN
+ // MIR for `mutborrow` after GVN

fn mutborrow() -> () {
let mut _0: ();
let mut _1: i32;
let _2: ();
let mut _3: i32;
let _5: ();
let mut _6: i32;
scope 1 {
debug x => _1;
let _4: &mut i32;
scope 2 {
debug r => _4;
}
}

bb0: {
StorageLive(_1);
_1 = const 42_i32;
StorageLive(_2);
StorageLive(_3);
- _3 = copy _1;
- _2 = opaque::<i32>(move _3) -> [return: bb1, unwind unreachable];
+ _3 = const 42_i32;
+ _2 = opaque::<i32>(const 42_i32) -> [return: bb1, unwind unreachable];
}

bb1: {
StorageDead(_3);
StorageDead(_2);
StorageLive(_4);
_4 = &mut _1;
StorageLive(_5);
StorageLive(_6);
_6 = copy _1;
_5 = opaque::<i32>(move _6) -> [return: bb2, unwind unreachable];
}

bb2: {
StorageDead(_6);
StorageDead(_5);
_0 = const ();
StorageDead(_4);
StorageDead(_1);
return;
}
}

50 changes: 50 additions & 0 deletions tests/mir-opt/const_prop/borrowed_variable.mutptr.GVN.diff
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Original file line number Diff line number Diff line change
@@ -0,0 +1,50 @@
- // MIR for `mutptr` before GVN
+ // MIR for `mutptr` after GVN

fn mutptr() -> () {
let mut _0: ();
let mut _1: i32;
let _2: ();
let mut _3: i32;
let _5: ();
let mut _6: i32;
scope 1 {
debug x => _1;
let _4: *mut i32;
scope 2 {
debug r => _4;
}
}

bb0: {
StorageLive(_1);
_1 = const 42_i32;
StorageLive(_2);
StorageLive(_3);
- _3 = copy _1;
- _2 = opaque::<i32>(move _3) -> [return: bb1, unwind unreachable];
+ _3 = const 42_i32;
+ _2 = opaque::<i32>(const 42_i32) -> [return: bb1, unwind unreachable];
}

bb1: {
StorageDead(_3);
StorageDead(_2);
StorageLive(_4);
_4 = &raw mut _1;
StorageLive(_5);
StorageLive(_6);
_6 = copy _1;
_5 = opaque::<i32>(move _6) -> [return: bb2, unwind unreachable];
}

bb2: {
StorageDead(_6);
StorageDead(_5);
_0 = const ();
StorageDead(_4);
StorageDead(_1);
return;
}
}

64 changes: 64 additions & 0 deletions tests/mir-opt/const_prop/borrowed_variable.nonfreeze.GVN.diff
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Original file line number Diff line number Diff line change
@@ -0,0 +1,64 @@
- // MIR for `nonfreeze` before GVN
+ // MIR for `nonfreeze` after GVN

fn nonfreeze(_1: T) -> () {
debug x => _1;
let mut _0: ();
let mut _2: T;
let _3: ();
let mut _4: T;
let _6: ();
let mut _7: T;
let _8: ();
let mut _9: T;
scope 1 {
debug y => _2;
let _5: &T;
scope 2 {
debug r => _5;
}
}

bb0: {
- StorageLive(_2);
+ nop;
_2 = copy _1;
StorageLive(_3);
StorageLive(_4);
_4 = copy _2;
- _3 = opaque::<T>(move _4) -> [return: bb1, unwind unreachable];
+ _3 = opaque::<T>(copy _2) -> [return: bb1, unwind unreachable];
}

bb1: {
StorageDead(_4);
StorageDead(_3);
StorageLive(_5);
_5 = &_1;
StorageLive(_6);
StorageLive(_7);
_7 = copy _1;
_6 = opaque::<T>(move _7) -> [return: bb2, unwind unreachable];
}

bb2: {
StorageDead(_7);
StorageDead(_6);
StorageLive(_8);
StorageLive(_9);
_9 = copy _2;
- _8 = opaque::<T>(move _9) -> [return: bb3, unwind unreachable];
+ _8 = opaque::<T>(copy _2) -> [return: bb3, unwind unreachable];
}

bb3: {
StorageDead(_9);
StorageDead(_8);
_0 = const ();
StorageDead(_5);
- StorageDead(_2);
+ nop;
return;
}
}

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