[SystemZ] Add check for INIT_UNDEF in getInstSizeInBytes

[tltao]

Due to some optimization changes, INIT_UNDEF is making its way to getInstSizeInBytes in llvm/lib/Target/SystemZ/SystemZLongBranch.cpp but we do not have an exception there in the assert. Since INIT_UNDEF is described as being similar to IMPLICIT_DEF and there is a check for IMPLICIT_DEF, it seems logical to also add a check for INIT_UNDEF.

[llvmbot]

@llvm/pr-subscribers-backend-systemz

Author: None (tltao)

Changes

Due to some optimization changes, INIT_UNDEF is making its way to getInstSizeInBytes in llvm/lib/Target/SystemZ/SystemZLongBranch.cpp but we do not have an exception there in the assert. Since INIT_UNDEF is described as being similar to IMPLICIT_DEF and there is a check for IMPLICIT_DEF, it seems logical to also add a check for INIT_UNDEF.

---

Full diff: https://github.com/llvm/llvm-project/pull/134661.diff

2 Files Affected:

• (modified) llvm/include/llvm/CodeGen/MachineInstr.h (+1)
• (modified) llvm/lib/Target/SystemZ/SystemZLongBranch.cpp (+1)

diff --git a/llvm/include/llvm/CodeGen/MachineInstr.h b/llvm/include/llvm/CodeGen/MachineInstr.h
index 102b1eb07358e..cd7b3055ad722 100644
--- a/llvm/include/llvm/CodeGen/MachineInstr.h
+++ b/llvm/include/llvm/CodeGen/MachineInstr.h
@@ -1409,6 +1409,7 @@ class MachineInstr
   }
   bool isKill() const { return getOpcode() == TargetOpcode::KILL; }
   bool isImplicitDef() const { return getOpcode()==TargetOpcode::IMPLICIT_DEF; }
+  bool isInitUndef() const { return getOpcode()==TargetOpcode::INIT_UNDEF; }
   bool isInlineAsm() const {
     return getOpcode() == TargetOpcode::INLINEASM ||
            getOpcode() == TargetOpcode::INLINEASM_BR;
diff --git a/llvm/lib/Target/SystemZ/SystemZLongBranch.cpp b/llvm/lib/Target/SystemZ/SystemZLongBranch.cpp
index f19b932f3c731..f0f33c960d822 100644
--- a/llvm/lib/Target/SystemZ/SystemZLongBranch.cpp
+++ b/llvm/lib/Target/SystemZ/SystemZLongBranch.cpp
@@ -218,6 +218,7 @@ static unsigned getInstSizeInBytes(const MachineInstr &MI,
           // These do not have a size:
           MI.isDebugOrPseudoInstr() || MI.isPosition() || MI.isKill() ||
           MI.isImplicitDef() || MI.getOpcode() == TargetOpcode::MEMBARRIER ||
+          MI.isInitUndef() ||
           // These have a size that may be zero:
           MI.isInlineAsm() || MI.getOpcode() == SystemZ::STACKMAP ||
           MI.getOpcode() == SystemZ::PATCHPOINT ||

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[nikic]

I don't think this is common enough to warrant a dedicated accessor.

[uweigand]

We probably should be more generic here and check for isMetaInstruction, which would also cover some of the existing special cases. However, INIT_UNDEF isn't currently even marked as isMeta - probably it should be, though.

[tltao]

We probably should be more generic here and check for isMetaInstruction, which would also cover some of the existing special cases. However, INIT_UNDEF isn't currently even marked as isMeta - probably it should be, though.

I believe @nikic tried this in the original PR #106744, but ultimately decided against it as it caused more changes. Perhaps a compromise can be to fix it with MI.getOpcode() == TargetOpcode::INIT_UNDEF for now?

[nikic]

This looks fine to me, but should it also have a test?

[uweigand]

LGTM, thanks!