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

[LuoYuanke via Phabricator via llvm-commits]

LuoYuanke 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:
> 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);

```


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D146862/new/

https://reviews.llvm.org/D146862