ISLE: Allow shadowing in let expressions (#4562)

* Support shadowing in isle

* Re-run the isle build.rs if the examples change

* Print error messages when isle tests fail

* Move run tests

* Refactor `let` uses that don't need to introduce unique names

cranelift/isle/isle/isle_examples/run/let_shadowing.isle

@@ -0,0 +1,38 @@
+
+(type u64 (primitive u64))
+
+(decl foo (u64) u64)
+(rule (foo x) x)
+
+;; Shadowing of a global name
+(decl test1 (u64) u64)
+(rule (test1 x)
+      (let ((foo u64 x))
+        foo))
+
+;; Shadowing of a parameter
+(decl test2 (u64) u64)
+(rule (test2 x)
+      (let ((x u64 x))
+        x))
+
+;; Shadowing of this binding's name
+(decl test3 (u64) u64)
+(rule (test3 x)
+      (let ((test3 u64 x))
+        test3))
+
+;; Shadowing another let-bound name
+(decl test4 (u64) u64)
+(rule (test4 x)
+      (let ((val u64 x)
+            (val u64 23))
+        val))
+
+;; Shadowing a global with a parameter name
+(decl test5 (u64) u64)
+(rule (test5 foo) foo)
+
+;; Using a previously shadowed global
+(decl test6 (u64) u64)
+(rule (test6 x) (foo x))

cranelift/isle/isle/isle_examples/run/let_shadowing_main.rs

@@ -0,0 +1,27 @@
+mod let_shadowing;
+
+struct Context;
+
+impl let_shadowing::Context for Context {}
+
+fn main() {
+    let mut ctx = Context;
+
+    assert_eq!(Some(20), let_shadowing::constructor_test1(&mut ctx, 20));
+    assert_eq!(Some(97), let_shadowing::constructor_test1(&mut ctx, 97));
+
+    assert_eq!(Some(20), let_shadowing::constructor_test2(&mut ctx, 20));
+    assert_eq!(Some(97), let_shadowing::constructor_test2(&mut ctx, 97));
+
+    assert_eq!(Some(20), let_shadowing::constructor_test3(&mut ctx, 20));
+    assert_eq!(Some(97), let_shadowing::constructor_test3(&mut ctx, 97));
+
+    assert_eq!(Some(23), let_shadowing::constructor_test4(&mut ctx, 20));
+    assert_eq!(Some(23), let_shadowing::constructor_test4(&mut ctx, 97));
+
+    assert_eq!(Some(20), let_shadowing::constructor_test5(&mut ctx, 20));
+    assert_eq!(Some(97), let_shadowing::constructor_test5(&mut ctx, 97));
+
+    assert_eq!(Some(20), let_shadowing::constructor_test6(&mut ctx, 20));
+    assert_eq!(Some(97), let_shadowing::constructor_test6(&mut ctx, 97));
+}