Auto merge of #106227 - bryangarza:ctfe-limit, r=oli-obk

Use stable metric for const eval limit instead of current terminator-based logic

This patch adds a `MirPass` that inserts a new MIR instruction `ConstEvalCounter` to any loops and function calls in the CFG. This instruction is used during Const Eval to count against the `const_eval_limit`, and emit the `StepLimitReached` error, replacing the current logic which uses Terminators only.

The new method of counting loops and function calls should be more stable across compiler versions (i.e., not cause crates that compiled successfully before, to no longer compile when changes to the MIR generation/optimization are made).

Also see: #103877

13 files changed, 224 insertions, 11 deletions

diff --git a/tests/ui/consts/const-eval/infinite_loop.stderr b/tests/ui/consts/const-eval/infinite_loop.stderr
index 8b58cb279f3..f30bfaf3f95 100644
--- a/tests/ui/consts/const-eval/infinite_loop.stderr
+++ b/tests/ui/consts/const-eval/infinite_loop.stderr
@@ -1,8 +1,11 @@
 error[E0080]: evaluation of constant value failed
-  --> $DIR/infinite_loop.rs:6:15
+  --> $DIR/infinite_loop.rs:6:9
    |
-LL |         while n != 0 {
-   |               ^^^^^^ exceeded interpreter step limit (see `#[const_eval_limit]`)
+LL | /         while n != 0 {
+LL | |
+LL | |             n = if n % 2 == 0 { n/2 } else { 3*n + 1 };
+LL | |         }
+   | |_________^ exceeded interpreter step limit (see `#[const_eval_limit]`)
 
 error: aborting due to previous error
 
diff --git a/tests/ui/consts/const-eval/issue-52475.rs b/tests/ui/consts/const-eval/issue-52475.rs
index ce65407bbab..307c1a66834 100644
--- a/tests/ui/consts/const-eval/issue-52475.rs
+++ b/tests/ui/consts/const-eval/issue-52475.rs
@@ -2,8 +2,8 @@ fn main() {
     let _ = [(); {
         let mut x = &0;
         let mut n = 0;
-        while n < 5 {
-            n = (n + 1) % 5; //~ ERROR evaluation of constant value failed
+        while n < 5 { //~ ERROR evaluation of constant value failed [E0080]
+            n = (n + 1) % 5;
             x = &0; // Materialize a new AllocId
         }
         0
diff --git a/tests/ui/consts/const-eval/issue-52475.stderr b/tests/ui/consts/const-eval/issue-52475.stderr
index 8536ff02c6d..3aa6bd277dd 100644
--- a/tests/ui/consts/const-eval/issue-52475.stderr
+++ b/tests/ui/consts/const-eval/issue-52475.stderr
@@ -1,8 +1,11 @@
 error[E0080]: evaluation of constant value failed
-  --> $DIR/issue-52475.rs:6:17
+  --> $DIR/issue-52475.rs:5:9
    |
-LL |             n = (n + 1) % 5;
-   |                 ^^^^^^^^^^^ exceeded interpreter step limit (see `#[const_eval_limit]`)
+LL | /         while n < 5 {
+LL | |             n = (n + 1) % 5;
+LL | |             x = &0; // Materialize a new AllocId
+LL | |         }
+   | |_________^ exceeded interpreter step limit (see `#[const_eval_limit]`)
 
 error: aborting due to previous error
 
diff --git a/tests/ui/consts/const-eval/stable-metric/ctfe-fn-call.rs b/tests/ui/consts/const-eval/stable-metric/ctfe-fn-call.rs
new file mode 100644
index 00000000000..c59596238e1
--- /dev/null
+++ b/tests/ui/consts/const-eval/stable-metric/ctfe-fn-call.rs
@@ -0,0 +1,36 @@
+// check-fail
+// compile-flags: -Z tiny-const-eval-limit
+
+const fn foo() {}
+
+const fn call_foo() -> u32 {
+    foo();
+    foo();
+    foo();
+    foo();
+    foo();
+
+    foo();
+    foo();
+    foo();
+    foo();
+    foo();
+
+    foo();
+    foo();
+    foo();
+    foo();
+    foo();
+
+    foo();
+    foo();
+    foo();
+    foo(); //~ ERROR evaluation of constant value failed [E0080]
+    0
+}
+
+const X: u32 = call_foo();
+
+fn main() {
+    println!("{X}");
+}
diff --git a/tests/ui/consts/const-eval/stable-metric/ctfe-fn-call.stderr b/tests/ui/consts/const-eval/stable-metric/ctfe-fn-call.stderr
new file mode 100644
index 00000000000..ed70975af34
--- /dev/null
+++ b/tests/ui/consts/const-eval/stable-metric/ctfe-fn-call.stderr
@@ -0,0 +1,20 @@
+error[E0080]: evaluation of constant value failed
+  --> $DIR/ctfe-fn-call.rs:28:5
+   |
+LL |     foo();
+   |     ^^^^^ exceeded interpreter step limit (see `#[const_eval_limit]`)
+   |
+note: inside `call_foo`
+  --> $DIR/ctfe-fn-call.rs:28:5
+   |
+LL |     foo();
+   |     ^^^^^
+note: inside `X`
+  --> $DIR/ctfe-fn-call.rs:32:16
+   |
+LL | const X: u32 = call_foo();
+   |                ^^^^^^^^^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0080`.
diff --git a/tests/ui/consts/const-eval/stable-metric/ctfe-labelled-loop.rs b/tests/ui/consts/const-eval/stable-metric/ctfe-labelled-loop.rs
new file mode 100644
index 00000000000..c10b8d83791
--- /dev/null
+++ b/tests/ui/consts/const-eval/stable-metric/ctfe-labelled-loop.rs
@@ -0,0 +1,19 @@
+// check-fail
+// compile-flags: -Z tiny-const-eval-limit
+
+const fn labelled_loop(n: u32) -> u32 {
+    let mut i = 0;
+    'mylabel: loop { //~ ERROR evaluation of constant value failed [E0080]
+        if i > n {
+            break 'mylabel
+        }
+        i += 1;
+    }
+    0
+}
+
+const X: u32 = labelled_loop(19);
+
+fn main() {
+    println!("{X}");
+}
diff --git a/tests/ui/consts/const-eval/stable-metric/ctfe-labelled-loop.stderr b/tests/ui/consts/const-eval/stable-metric/ctfe-labelled-loop.stderr
new file mode 100644
index 00000000000..d9404edd5b1
--- /dev/null
+++ b/tests/ui/consts/const-eval/stable-metric/ctfe-labelled-loop.stderr
@@ -0,0 +1,30 @@
+error[E0080]: evaluation of constant value failed
+  --> $DIR/ctfe-labelled-loop.rs:6:5
+   |
+LL | /     'mylabel: loop {
+LL | |         if i > n {
+LL | |             break 'mylabel
+LL | |         }
+LL | |         i += 1;
+LL | |     }
+   | |_____^ exceeded interpreter step limit (see `#[const_eval_limit]`)
+   |
+note: inside `labelled_loop`
+  --> $DIR/ctfe-labelled-loop.rs:6:5
+   |
+LL | /     'mylabel: loop {
+LL | |         if i > n {
+LL | |             break 'mylabel
+LL | |         }
+LL | |         i += 1;
+LL | |     }
+   | |_____^
+note: inside `X`
+  --> $DIR/ctfe-labelled-loop.rs:15:16
+   |
+LL | const X: u32 = labelled_loop(19);
+   |                ^^^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0080`.
diff --git a/tests/ui/consts/const-eval/stable-metric/ctfe-recursion.rs b/tests/ui/consts/const-eval/stable-metric/ctfe-recursion.rs
new file mode 100644
index 00000000000..80ff835f3e8
--- /dev/null
+++ b/tests/ui/consts/const-eval/stable-metric/ctfe-recursion.rs
@@ -0,0 +1,16 @@
+// check-fail
+// compile-flags: -Z tiny-const-eval-limit
+
+const fn recurse(n: u32) -> u32 {
+    if n == 0 {
+        n
+    } else {
+        recurse(n - 1) //~ ERROR evaluation of constant value failed [E0080]
+    }
+}
+
+const X: u32 = recurse(19);
+
+fn main() {
+    println!("{X}");
+}
diff --git a/tests/ui/consts/const-eval/stable-metric/ctfe-recursion.stderr b/tests/ui/consts/const-eval/stable-metric/ctfe-recursion.stderr
new file mode 100644
index 00000000000..ed9a3111942
--- /dev/null
+++ b/tests/ui/consts/const-eval/stable-metric/ctfe-recursion.stderr
@@ -0,0 +1,25 @@
+error[E0080]: evaluation of constant value failed
+  --> $DIR/ctfe-recursion.rs:8:9
+   |
+LL |         recurse(n - 1)
+   |         ^^^^^^^^^^^^^^ exceeded interpreter step limit (see `#[const_eval_limit]`)
+   |
+note: inside `recurse`
+  --> $DIR/ctfe-recursion.rs:8:9
+   |
+LL |         recurse(n - 1)
+   |         ^^^^^^^^^^^^^^
+note: [... 18 additional calls inside `recurse` ...]
+  --> $DIR/ctfe-recursion.rs:8:9
+   |
+LL |         recurse(n - 1)
+   |         ^^^^^^^^^^^^^^
+note: inside `X`
+  --> $DIR/ctfe-recursion.rs:12:16
+   |
+LL | const X: u32 = recurse(19);
+   |                ^^^^^^^^^^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0080`.
diff --git a/tests/ui/consts/const-eval/stable-metric/ctfe-simple-loop.rs b/tests/ui/consts/const-eval/stable-metric/ctfe-simple-loop.rs
new file mode 100644
index 00000000000..ca0eec93c5d
--- /dev/null
+++ b/tests/ui/consts/const-eval/stable-metric/ctfe-simple-loop.rs
@@ -0,0 +1,15 @@
+// check-fail
+// compile-flags: -Z tiny-const-eval-limit
+const fn simple_loop(n: u32) -> u32 {
+    let mut index = 0;
+    while index < n { //~ ERROR evaluation of constant value failed [E0080]
+        index = index + 1;
+    }
+    0
+}
+
+const X: u32 = simple_loop(19);
+
+fn main() {
+    println!("{X}");
+}
diff --git a/tests/ui/consts/const-eval/stable-metric/ctfe-simple-loop.stderr b/tests/ui/consts/const-eval/stable-metric/ctfe-simple-loop.stderr
new file mode 100644
index 00000000000..83ff275de70
--- /dev/null
+++ b/tests/ui/consts/const-eval/stable-metric/ctfe-simple-loop.stderr
@@ -0,0 +1,24 @@
+error[E0080]: evaluation of constant value failed
+  --> $DIR/ctfe-simple-loop.rs:5:5
+   |
+LL | /     while index < n {
+LL | |         index = index + 1;
+LL | |     }
+   | |_____^ exceeded interpreter step limit (see `#[const_eval_limit]`)
+   |
+note: inside `simple_loop`
+  --> $DIR/ctfe-simple-loop.rs:5:5
+   |
+LL | /     while index < n {
+LL | |         index = index + 1;
+LL | |     }
+   | |_____^
+note: inside `X`
+  --> $DIR/ctfe-simple-loop.rs:11:16
+   |
+LL | const X: u32 = simple_loop(19);
+   |                ^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0080`.
diff --git a/tests/ui/consts/const-eval/stable-metric/dominators-edge-case.rs b/tests/ui/consts/const-eval/stable-metric/dominators-edge-case.rs
new file mode 100644
index 00000000000..0b0f361809f
--- /dev/null
+++ b/tests/ui/consts/const-eval/stable-metric/dominators-edge-case.rs
@@ -0,0 +1,19 @@
+// check-pass
+//
+// Exercising an edge case which was found during Stage 2 compilation.
+// Compilation would fail for this code when running the `CtfeLimit`
+// MirPass (specifically when looking up the dominators).
+#![crate_type="lib"]
+
+const DUMMY: Expr = Expr::Path(ExprPath {
+    attrs: Vec::new(),
+    path: Vec::new(),
+});
+
+pub enum Expr {
+    Path(ExprPath),
+}
+pub struct ExprPath {
+    pub attrs: Vec<()>,
+    pub path: Vec<()>,
+}
diff --git a/tests/ui/consts/const_limit/const_eval_limit_reached.stderr b/tests/ui/consts/const_limit/const_eval_limit_reached.stderr
index 850aebdfb2a..a8e8ae9bb08 100644
--- a/tests/ui/consts/const_limit/const_eval_limit_reached.stderr
+++ b/tests/ui/consts/const_limit/const_eval_limit_reached.stderr
@@ -1,8 +1,11 @@
 error[E0080]: evaluation of constant value failed
-  --> $DIR/const_eval_limit_reached.rs:6:11
+  --> $DIR/const_eval_limit_reached.rs:6:5
    |
-LL |     while x != 1000 {
-   |           ^^^^^^^^^ exceeded interpreter step limit (see `#[const_eval_limit]`)
+LL | /     while x != 1000 {
+LL | |
+LL | |         x += 1;
+LL | |     }
+   | |_____^ exceeded interpreter step limit (see `#[const_eval_limit]`)
 
 error: aborting due to previous error