Cranelift: Add egraph rule to rewrite x * C ==> x << log2(C) when C is a power of two (#5647)

cranelift/filetests/filetests/egraph/algebraic.clif

@@ -7,8 +7,8 @@ function %f0(i32) -> i32 {
 block0(v0: i32):
     v1 = iconst.i32 2
     v2 = imul v0, v1
-    ; check: v3 = iadd v0, v0
-    ; check: return v3
+    ; check: v5 = ishl v0, v4  ; v4 = 1
+    ; check: return v5
     return v2
 }
 

cranelift/filetests/filetests/egraph/mul-pow-2.clif

@@ -0,0 +1,34 @@
+test optimize
+set opt_level=speed
+set use_egraphs=true
+target x86_64
+
+function %f0(i32) -> i32 {
+block0(v0: i32):
+    v1 = iconst.i32 4
+    v2 = imul v0, v1
+    ; check:  v3 = iconst.i32 2
+    ; nextln: v4 = ishl v0, v3
+    ; check:  return v4
+    return v2
+}
+
+function %f1(i32) -> i32 {
+block0(v0: i32):
+    v1 = iconst.i32 8
+    v2 = imul v0, v1
+    ; check:  v3 = iconst.i32 3
+    ; nextln: v4 = ishl v0, v3
+    ; check:  return v4
+    return v2
+}
+
+function %f2(i32) -> i32 {
+block0(v0: i32):
+    v1 = iconst.i32 16
+    v2 = imul v0, v1
+    ; check:  v3 = iconst.i32 4
+    ; nextln: v4 = ishl v0, v3
+    ; check:  return v4
+    return v2
+}

cranelift/filetests/src/subtest.rs

@@ -107,6 +107,12 @@ pub trait SubTest {
 
 /// Run filecheck on `text`, using directives extracted from `context`.
 pub fn run_filecheck(text: &str, context: &Context) -> anyhow::Result<()> {
+    log::debug!(
+        "Filecheck Input:\n\
+         =======================\n\
+         {text}\n\
+         ======================="
+    );
     let checker = build_filechecker(context)?;
     if checker
         .check(text, NO_VARIABLES)