Fix gvn alias bug

crates/codegen/src/optim/gvn.rs

@@ -1334,6 +1334,8 @@ struct RedundantCodeRemover<'a> {
 
     /// Record resolved value phis.
     resolved_value_phis: FxHashMap<ValuePhi, Value>,
+
+    renames: FxHashMap<Value, Value>,
 }
 
 impl<'a> RedundantCodeRemover<'a> {
@@ -1342,7 +1344,23 @@ impl<'a> RedundantCodeRemover<'a> {
             solver,
             avail_set: SecondaryMap::default(),
             resolved_value_phis: FxHashMap::default(),
+            renames: FxHashMap::default(),
+        }
+    }
+
+    fn change_to_alias(&mut self, func: &mut Function, value: Value, target: Value) {
+        func.dfg.change_to_alias(value, target);
+        self.renames.insert(value, target);
+    }
+
+    fn resolve_alias(&self, mut value: Value) -> Value {
+        for _ in 0..1 + self.renames.len() {
+            match self.renames.get(&value) {
+                Some(v) => value = *v,
+                None => return value,
+            }
         }
+        panic!("alias loop detected");
     }
 
     /// The entry function of redundant code removal.
@@ -1421,7 +1439,7 @@ impl<'a> RedundantCodeRemover<'a> {
 
                         // Use representative value if the class is in avail set.
                         if let Some(value) = avails.get(&class) {
-                            func.dfg.change_to_alias(insn_result, *value);
+                            self.change_to_alias(func, insn_result, *value);
                             inserter.remove_insn(func);
                             continue;
                         }
@@ -1469,7 +1487,8 @@ impl<'a> RedundantCodeRemover<'a> {
                                     ty,
                                     block,
                                 );
-                                func.dfg.change_to_alias(insn_result, value);
+
+                                self.change_to_alias(func, insn_result, value);
                                 inserter.remove_insn(func);
                                 continue;
                             }
@@ -1537,7 +1556,7 @@ impl<'a> RedundantCodeRemover<'a> {
                 for (value_phi, phi_block) in &phi_insn.args {
                     let resolved =
                         self.resolve_value_phi(func, inserter, value_phi, ty, *phi_block);
-                    phi.append_phi_arg(resolved, *phi_block);
+                    phi.append_phi_arg(self.resolve_alias(resolved), *phi_block);
                 }
 
                 // Insert new phi insn to top of the phi_insn block.

crates/ir/src/dfg.rs

@@ -249,6 +249,7 @@ impl DataFlowGraph {
     }
 
     pub fn remove_branch_dest(&mut self, insn: Insn, dest: Block) {
+        // xxx remove user
         self.insns[insn].remove_branch_dest(dest)
     }
 

crates/ir/src/insn.rs

@@ -48,16 +48,10 @@ impl<'a> fmt::Display for DisplayInsn<'a> {
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub enum InsnData {
     /// Unary instructions.
-    Unary {
-        code: UnaryOp,
-        args: [Value; 1],
-    },
+    Unary { code: UnaryOp, args: [Value; 1] },
 
     /// Binary instructions.
-    Binary {
-        code: BinaryOp,
-        args: [Value; 2],
-    },
+    Binary { code: BinaryOp, args: [Value; 2] },
 
     /// Cast operations.
     Cast {
@@ -86,15 +80,10 @@ pub enum InsnData {
     },
 
     /// Unconditional jump instruction.
-    Jump {
-        dests: [Block; 1],
-    },
+    Jump { dests: [Block; 1] },
 
     /// Conditional jump instruction.
-    Branch {
-        args: [Value; 1],
-        dests: [Block; 2],
-    },
+    Branch { args: [Value; 1], dests: [Block; 2] },
 
     /// Indirect jump instruction.
     BrTable {
@@ -104,18 +93,13 @@ pub enum InsnData {
     },
 
     /// Allocate a memory on the stack frame for the given type.
-    Alloca {
-        ty: Type,
-    },
+    Alloca { ty: Type },
 
     /// Return.
-    Return {
-        args: Option<Value>,
-    },
+    Return { args: Option<Value> },
 
-    Gep {
-        args: SmallVec<[Value; 8]>,
-    },
+    /// Get element pointer.
+    Gep { args: SmallVec<[Value; 8]> },
 
     /// Phi function.
     Phi {
@@ -239,6 +223,7 @@ impl InsnData {
                 if Some(dest) == *default {
                     *default = None;
                 } else {
+                    // xxx remove user
                     table.retain(|block| dest != *block);
                 }
 
@@ -374,10 +359,6 @@ impl InsnData {
         }
     }
 
-    pub fn replace_arg(&mut self, new_arg: Value, idx: usize) {
-        self.args_mut()[idx] = new_arg;
-    }
-
     pub fn is_phi(&self) -> bool {
         matches!(self, InsnData::Phi { .. })
     }