[LLVMdev] [x86] Compiling in 32-bit mode causes 64-bit asm source to be silently converted to its 32-bit equavilent

[Craig Topper]

Forgot to copy llvmdev.

I think this part of the diff was a mistake. That Requires check still
needs to be there.

   let Uses = [RCX] in
     def JRCXZ : Ii8PCRel<0xE3, RawFrm, (outs), (ins brtarget8:$dst),
-                           "jrcxz\t$dst", [], IIC_JCXZ>, AdSize64,
Requires<[In64BitMode]>;
+                           "jrcxz\t$dst", [], IIC_JCXZ>, AdSize64;


I'll fix sometime this weekend.


On Thu, Jul 2, 2015 at 3:55 PM, Li, Charles <charles_li at playstation.sony.com
> wrote:

>  Hi Craig,
>
>
>
> I am Charles Li from Sony Playstation.
>
>
>
> We are doing x86 code gen testing and, by chance, we noticed that
> compiling the 64-bit assembly instruction
> <https://msdn.microsoft.com/en-us/library/windows/hardware/ff561499(v=vs.85).aspx>
> “jrcxz” in 32-bit mode “-m32”
>
> previously resulted in an error,
>
> now gets silently converted into the 32-bit equivalent instruction “jecxz
> ”.
> I have bisected this change in behavior down to r225075 - [X86] Make the
> instructions that use AdSize16/32/64 co-exist together without using mode
> predicates.
> <http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20141229/250681.html>
>
> I am curious if this change in behavior was an intended feature or perhaps
> a side effect.
>
>
>
>
>
> Here is my methodology.
>
> The asm test case.
>
> $ cat j64.s
>
>         jrcxz   foo
>
> foo:
>
>
>
> Compiling the test case in 32-bit mode with Clang r225039.
>
> $ r225039/clang.exe  j64.s -c -m32  -target x86_64-pc-linux-gnu
>
> j64.s:1:9: error: instruction requires: 64-bit mode
>
>         jrcxz   foo
>
>         ^
>
>
>
> Compiling the test case in 32-bit mode with Clang r225079 then
> disassembling the obj file to look for the jump instruction.
>
> $ r225079/clang.exe  j64.s -c -m32  -target x86_64-pc-linux-gnu
>
> (No Error)
>
>
>
> $ objdump j64.o -d | grep j
>
> j64.o:     file format elf32-i386
>
>    0:   e3 00                   jecxz  2 <foo>
>
>
> Just FYI, this is not blocking us in any way. I found this to be a very
> interesting discovery so I want to share it in the hopes of determining if
> it was intentional or not.
>
>
>
> Sincerely,
>
> Charles Li
>



-- 
~Craig
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