chore: add an assertion when parsing SSA that all functions are well-formed

compiler/noirc_evaluator/src/ssa/ir/function.rs

@@ -231,6 +231,28 @@ impl Function {
             }
         })
     }
+
+    /// Asserts that the [`Function`] is well formed.
+    ///
+    /// Panics on malformed functions.
+    pub(crate) fn assert_valid(&self) {
+        let reachable_blocks = self.reachable_blocks();
+
+        // We assume that all functions have a single block which terminates with a `return` instruction.
+        let return_blocks: BTreeSet<_> = reachable_blocks
+            .iter()
+            .filter(|block| {
+                // All blocks must have a terminator instruction of some sort.
+                let terminator = self.dfg[**block].terminator().unwrap_or_else(|| {
+                    panic!("Function {} has no terminator in block {block}", self.id())
+                });
+                matches!(terminator, TerminatorInstruction::Return { .. })
+            })
+            .collect();
+        if return_blocks.len() > 1 {
+            panic!("Function {} has multiple return blocks {return_blocks:?}", self.id())
+        }
+    }
 }
 
 impl Clone for Function {

compiler/noirc_evaluator/src/ssa/opt/inlining.rs

@@ -816,12 +816,14 @@ mod test {
             v2 = lt v1, u32 1
             jmpif v2 then: b1, else: b2
           b1():
-            return u32 1
+            jmp b3(u32 1)
           b2():
             v4 = sub v1, u32 1
             v5 = call f1(v4) -> u32
             v6 = mul v1, v5
-            return v6
+            jmp b3(v6)
+          b3(v7: u32):
+            return v7
         }
         ";
         let ssa = Ssa::from_str(src).unwrap();
@@ -842,7 +844,23 @@ mod test {
           b5():
             jmp b6()
           b6():
-            return u32 120
+            jmp b7(u32 1)
+          b7(v0: u32):
+            jmp b8(v0)
+          b8(v1: u32):
+            v8 = mul u32 2, v1
+            jmp b9(v8)
+          b9(v2: u32):
+            v10 = mul u32 3, v2
+            jmp b10(v10)
+          b10(v3: u32):
+            v12 = mul u32 4, v3
+            jmp b11(v12)
+          b11(v4: u32):
+            v14 = mul u32 5, v4
+            jmp b12(v14)
+          b12(v5: u32):
+            return v5
         }
         ");
     }

compiler/noirc_evaluator/src/ssa/opt/simplify_cfg.rs

@@ -349,7 +349,7 @@ mod test {
           b1():
             return Field 1
           b2():
-            return Field 2
+            jmp b1()
         }
         ";
         let ssa = Ssa::from_str(src).unwrap();

compiler/noirc_evaluator/src/ssa/parser/into_ssa.rs

@@ -503,6 +503,10 @@ impl Translator {
         // before each print.
         ssa.normalize_ids();
 
+        for function in ssa.functions.values() {
+            function.assert_valid();
+        }
+
         ssa
     }
 

compiler/noirc_evaluator/src/ssa/parser/tests.rs

@@ -170,7 +170,7 @@ fn test_jmpif() {
           b0(v0: Field):
             jmpif v0 then: b1, else: b2
           b1():
-            return
+            jmp b2()
           b2():
             return
         }
@@ -182,7 +182,7 @@ fn test_jmpif() {
           b0(v0: Field):
             jmpif v0 then: b2, else: b1
           b1():
-            return
+            jmp b2()
           b2():
             return
         }
@@ -197,10 +197,12 @@ fn test_multiple_jmpif() {
           b0(v0: Field, v1: Field):
             jmpif v0 then: b1, else: b2
           b1():
-            return
+            jmp b4()
           b2():
             jmpif v1 then: b3, else: b1
           b3():
+            jmp b4()
+          b4():
             return
         }
     ";