method with parameter requiring null check and class cast check

[Christian Thalinger]

On Jan 2, 2014, at 10:11 AM, Deneau, Tom <tom.deneau at amd.com> wrote:

> I ran the following code thru the AMD64 backend with -G:-OptImplicitNullChecks.
> So this should generate both a null check and a class cast check on the input parameter.
> 
> Below I show the code I got.  See my questions inline below…

What are the actual questions?  Why there are these additional null checks?

One thing I find odd is that the path on which the cast succeeds is out-of-line and not a fall-through.  How did you compile this method?  Was there some profiling going on before?

> 
> -- Tom
> 
> 
>    static class Vec3 {
> 
>        public Vec3(float x, float y, float z) {
>            this.x = x;
>            this.y = y;
>            this.z = z;
>        }
> 
>        public float x;
>        public float y;
>        public float z;
>    }
> 
>    static class MyVec3 extends Vec3 {
>        public MyVec3(float x, float y, float z) {
>            super(x, y, z);
>        }
>    }
> 
> 
>    public void runvec3(Vec3 vec3) {
>        MyVec3 myvec3 = (MyVec3) vec3;
>        myvec3.z = myvec3.x + myvec3.y;
>    }
> 
> 
> 
> 
> ========================================
> [Verified Entry Point]
>  0x00007fc7fc5c8880: mov    qword ptr [rsp-0x14000],rax
>  0x00007fc7fc5c8888: sub    rsp,0x18
>  0x00007fc7fc5c888c: mov    qword ptr [rsp+0x10],rbp  ; OopMap{rdx=Oop off=49}
>                                                ;*aload_1
>                                                ; - com.oracle.graal.compiler.test.BasicTest2::runvec3 at 0 (line 67)
> 
>  0x00007fc7fc5c8891: test   dword ptr [rdx],eax
>  0x00007fc7fc5c8893: cmp    rdx,0x0
>  0x00007fc7fc5c8897: je     0x00007fc7fc5c88fa         ;; if null take path as if class cast did not match...
> 
>  ;; odd to have both an implicit and explicit null check here but I think that's related to the GuardLoweringPhase
>  ;; thing I mentioned in an earlier email.  If I fix that issue in GuardLoweringPhase, the test instruction
>  ;; becomes an explicit null check which goes to a null check deopt.
>  ;; But in either case the second null check seems unnecessary.
> 
>  0x00007fc7fc5c889d: mov    eax,dword ptr [rdx+0x8]     ;; checking the class of the parameter
>  0x00007fc7fc5c88a0: shl    rax,0x3
>  0x00007fc7fc5c88a4: movabs rbx,0x100109c28
>  0x00007fc7fc5c88ae: cmp    rbx,rax
>  0x00007fc7fc5c88b1: je     0x00007fc7fc5c88f3             
>  0x00007fc7fc5c88b7: mov    eax,0x0                     ;; eax == 0 means class cast problem, not exact match
> 
>  0x00007fc7fc5c88bc: cmp    rdx,0x0                     ;; this third null check seems unnecessary.
>  0x00007fc7fc5c88c0: je     0x00007fc7fc5c88cf
>  0x00007fc7fc5c88c6: cmp    eax,0x1                     ;; compare whether class cast worked
>  0x00007fc7fc5c88c9: jne    0x00007fc7fc5c8901          ;; if not go to class cast deopt
>  0x00007fc7fc5c88cf: movss  xmm0,dword ptr [rdx+0xc]    ;; class cast ok, do the real work
>  0x00007fc7fc5c88d4: movss  xmm1,dword ptr [rdx+0x10]
>  0x00007fc7fc5c88d9: addss  xmm1,xmm0
>  0x00007fc7fc5c88dd: movss  dword ptr [rdx+0x14],xmm1
>  0x00007fc7fc5c88e2: mov    rbp,qword ptr [rsp+0x10]
>  0x00007fc7fc5c88e7: add    rsp,0x18
>  0x00007fc7fc5c88eb: mov    rbx,qword ptr [rip+0x1b37e715]        # 0x00007fc817947007
>                                                ;   {poll_return}
>  0x00007fc7fc5c88f2: ret    
>  0x00007fc7fc5c88f3: mov    eax,0x1                     ;; eax == 1 means class cast worked, not exact match
>  0x00007fc7fc5c88f8: jmp    0x00007fc7fc5c88bc
>  0x00007fc7fc5c88fa: mov    eax,0x0
>  0x00007fc7fc5c88ff: jmp    0x00007fc7fc5c88bc
>  0x00007fc7fc5c8901: mov    dword ptr [r15+0x8],0xffffffdd                   ;; class cast deopt
>  0x00007fc7fc5c8909: call   0x00007fc7fc046bf3  ; OopMap{rdx=Oop off=174}
>                                                ;*aload_1
>                                                ; - com.oracle.graal.compiler.test.BasicTest2::runvec3 at 0 (line 67)
>                                                ;   {runtime_call}
>  0x00007fc7fc5c890e: nop
> [Exception Handler]
>  0x00007fc7fc5c890f: call   0x00007fc7fc5c8520  ;   {runtime_call}
>  0x00007fc7fc5c8914: nop
> [Deopt Handler Code]
>  0x00007fc7fc5c8915: call   0x00007fc7fc046b00  ;   {runtime_call}
>  0x00007fc7fc5c891a: nop
> [Stub Code]
>  0x00007fc7fc5c891b: hlt    
>  0x00007fc7fc5c891c: hlt    
>  0x00007fc7fc5c891d: hlt    
>  0x00007fc7fc5c891e: hlt    
>  0x00007fc7fc5c891f: hlt    
> 
> 
> 
> 
>