[PATCH] D146862: [X86] Fix the incorrect displacement for prolog/epilog

[Phoebe Wang via Phabricator via llvm-commits]

pengfei added inline comments.


================
Comment at: llvm/lib/Target/X86/X86FrameLowering.cpp:1590
     BuildStackAlignAND(MBB, MBBI, DL, StackPtr, MaxAlign);
-    int64_t Offset = Is64Bit ? -2 * (int64_t)SlotSize : -1 * (int64_t)SlotSize;
+    int64_t Offset = -1 * (int64_t)SlotSize;
     BuildMI(MBB, MBBI, DL, TII.get(Is64Bit ? X86::PUSH64rmm: X86::PUSH32rmm))
----------------
LuoYuanke wrote:
> LuoYuanke wrote:
> > pengfei wrote:
> > > Curious why using 2 before. I was thinking it's related to stack aligement. AFAIK, Windows requires the stack always aligned to 16B on 64-bits.
> > > 
> > > Is better to directly `int64_t Offset = -SlotSize`?
> > Because my previous version is to push a callee saved register `push %rbx` as well, and then I realized that it is more complex on unwind support, and I turn to a scratch register which doesn't need to be saved and restore. But I forget to modify the offset. I'm developing a runtime test case to cover this issue.
> I got regression with below change. It is wired to me. Maybe it is due to the type of SlotSize is `unsigned`.
> 
> ```
> diff --git a/llvm/lib/Target/X86/X86FrameLowering.cpp b/llvm/lib/Target/X86/X86FrameLowering.cpp
> index 15f39a509e1a..f3f21f0ac46d 100644
> --- a/llvm/lib/Target/X86/X86FrameLowering.cpp
> +++ b/llvm/lib/Target/X86/X86FrameLowering.cpp
> @@ -1587,7 +1587,7 @@ void X86FrameLowering::emitPrologue(MachineFunction &MF,
>                 MachineInstr::FrameSetup);
>      }
>      BuildStackAlignAND(MBB, MBBI, DL, StackPtr, MaxAlign);
> -    int64_t Offset = -1 * (int64_t)SlotSize;
> +    int64_t Offset = -SlotSize;
>      BuildMI(MBB, MBBI, DL, TII.get(Is64Bit ? X86::PUSH64rmm: X86::PUSH32rmm))
>          .addReg(ArgBaseReg)
>          .addImm(1)
> @@ -2324,6 +2324,7 @@ void X86FrameLowering::emitEpilogue(MachineFunction &MF,
>          .addUse(ArgBaseReg)
>          .addImm(1)
>          .addUse(X86::NoRegister)
> +        // .addImm((int64_t)-SlotSize)
>          .addImm((int64_t)SlotSize * -1)
>          .addUse(X86::NoRegister)
>          .setMIFlag(MachineInstr::FrameDestroy);
> 
> ```
How about `-(int64_t)SlotSize`?


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D146862/new/

https://reviews.llvm.org/D146862