fixes

Author: KGrewal1

cranelift/codegen/src/isle_prelude.rs

@@ -37,6 +37,19 @@ macro_rules! isle_common_prelude_methods {
             Imm64::new(i64::from(lz))
         }
 
+        #[inline]
+        fn imm64_ctz(&mut self, ty: Type, a: Imm64) -> Imm64 {
+            let bits = ty.bits();
+            assert!(bits <= 64);
+            let a_v: u64 = a.bits().cast_unsigned();
+            if a_v == 0 {
+                // ctz(0) is defined to be the number of bits in the type.
+                return Imm64::new(i64::from(bits));
+            }
+            let lz = a_v.trailing_zeros();
+            Imm64::new(i64::from(lz))
+        }
+
         #[inline]
         fn imm64_sdiv(&mut self, ty: Type, x: Imm64, y: Imm64) -> Option<Imm64> {
             // Sign extend `x` and `y`.

cranelift/codegen/src/opts/cprop.isle

@@ -1,15 +1,15 @@
 ;; Constant propagation.
 
 (rule (simplify
-       (clz (fits_in_64 ty)
-             (iconst ty kx)))
+      (clz (fits_in_64 ty)
+            (iconst ty kx)))
       (subsume (iconst ty (imm64_clz ty kx))))
 
 
 (rule (simplify
        (ctz (fits_in_64 ty)
-             (iconst ty (u64_from_imm64 kx))))
-      (subsume (iconst ty (imm64_masked ty (u64_trailing_zeros kx)))))
+             (iconst ty kx)))
+      (subsume (iconst ty (imm64_ctz ty kx))))
 
 (rule (simplify
        (iadd (fits_in_64 ty)

cranelift/codegen/src/prelude.isle

@@ -102,6 +102,8 @@
 (decl pure imm64_clz (Type Imm64) Imm64)
 (extern constructor imm64_clz imm64_clz)
 
+(decl pure imm64_ctz (Type Imm64) Imm64)
+(extern constructor imm64_ctz imm64_ctz)
 
 ;; Each of these extractors tests whether the upper half of the input equals the
 ;; lower half of the input

cranelift/filetests/filetests/egraph/cprop.clif

@@ -49,6 +49,16 @@ block0:
 ; check: v3 = iconst.i16 4
 ; nextln: return v3
 
+function %f0() -> i16 {
+block0:
+    v1 = iconst.i16 0
+    v2 = ctz.i16 v1
+    return v2
+}
+
+; check: v3 = iconst.i16 16
+; nextln: return v3
+
 function %ishl() -> i8 {
 block0:
     v0 = iconst.i8 1