fix issue 5525. (#5603)

* fix issue 5525.

* reg alloc changed.

cranelift/filetests/filetests/isa/riscv64/extend-op.clif

@@ -66,8 +66,8 @@ block0(v0: i32):
 }
 
 ; block0:
-;   sext.w t2,a0
-;   slt a1,t2,zero
+;   sext.w a0,a0
+;   slt a1,a0,zero
 ;   sext.b1 a1,a1
 ;   ret
 
@@ -89,8 +89,8 @@ block0(v0: i16):
 }
 
 ; block0:
-;   sext.h t2,a0
-;   slt a1,t2,zero
+;   sext.h a0,a0
+;   slt a1,a0,zero
 ;   sext.b1 a1,a1
 ;   ret
 
@@ -112,8 +112,8 @@ block0(v0: i8):
 }
 
 ; block0:
-;   sext.b t2,a0
-;   slt a1,t2,zero
+;   sext.b a0,a0
+;   slt a1,a0,zero
 ;   sext.b1 a1,a1
 ;   ret
 

cranelift/filetests/filetests/runtests/issue5525.clif

@@ -0,0 +1,12 @@
+test interpret
+test run
+target riscv64
+
+function %a(i16) -> i128 system_v {
+block0(v0: i16):
+    v1 = rotl v0, v0
+    v2 = sextend.i128 v1
+    return v2
+}
+
+; run: %a(-32718) == 202