Remove unwrap() for branch folding

cranelift/filetests/filetests/preopt/branch.clif

@@ -52,3 +52,28 @@ ebb2:
 ; nextln:     v2 = iconst.i32 24
 ; nextln:     return v2
 ; nextln: }
+
+function %brz_fold_param(b1) -> i32 {
+ebb0(v0: b1):
+    brz v0, ebb2
+    jump ebb1
+ebb1:
+    v1 = iconst.i32 42
+    return v1
+ebb2:
+    v2 = iconst.i32 24
+    return v2
+}
+; sameln: function %brz_fold_param(b1) -> i32 fast {
+; nextln: ebb0(v0: b1):
+; nextln:     brz v0, ebb2
+; nextln:     jump ebb1
+; nextln: 
+; nextln: ebb1:
+; nextln:     v1 = iconst.i32 42
+; nextln:     return v1
+; nextln: 
+; nextln: ebb2:
+; nextln:     v2 = iconst.i32 24
+; nextln:     return v2
+; nextln: }

cranelift/preopt/src/constant_folding.rs

@@ -232,7 +232,10 @@ fn fold_branch(pos: &mut FuncCursor, inst: ir::Inst, opcode: ir::Opcode) {
         let values = pos.func.dfg.inst_args(inst);
         let inst_data = &pos.func.dfg[inst];
         (
-            resolve_value_to_imm(&pos.func.dfg, values[0]).unwrap(),
+            match resolve_value_to_imm(&pos.func.dfg, values[0]) {
+                Some(imm) => imm,
+                None => return,
+            },
             inst_data.branch_destination().unwrap(),
             values[1..].to_vec(),
         )