Cope with MCOperand null Insts

[urnathan]

I encountered a bolt segfault due to an MCOperand of type Inst with a null pointer. It seems bolt is intentionally creating such operands, so it would be good for the printer to not barf on them.

The bolt code is bolt/include/bolt/Core/MCPlusBuilder.h where the annotation machinery is. For example line 131 in setAnnotationOpValue:
Inst.addOperand(MCOperand::createInst(nullptr));

In my case it was annotating an X86 JCC instruction, and using --debug crashed.

[llvmbot]

@llvm/pr-subscribers-mc

Author: Nathan Sidwell (urnathan)

Changes

I encountered a bolt segfault due to an MCOperand of type Inst with a null pointer. It seems bolt is intentionally creating such operands, so it would be good for the printer to not barf on them.

The bolt code is bolt/include/bolt/Core/MCPlusBuilder.h where the annotation machinery is. For example line 131 in setAnnotationOpValue:
Inst.addOperand(MCOperand::createInst(nullptr));

In my case it was annotating an X86 JCC instruction, and using --debug crashed.

---

Full diff: https://github.com/llvm/llvm-project/pull/91794.diff

1 Files Affected:

• (modified) llvm/lib/MC/MCInst.cpp (+4-1)

diff --git a/llvm/lib/MC/MCInst.cpp b/llvm/lib/MC/MCInst.cpp
index 3cc50ff43513e..639619fe4e991 100644
--- a/llvm/lib/MC/MCInst.cpp
+++ b/llvm/lib/MC/MCInst.cpp
@@ -38,7 +38,10 @@ void MCOperand::print(raw_ostream &OS, const MCRegisterInfo *RegInfo) const {
     OS << "Expr:(" << *getExpr() << ")";
   } else if (isInst()) {
     OS << "Inst:(";
-    getInst()->print(OS, RegInfo);
+    if (const auto *Inst = getInst())
+      Inst->print(OS, RegInfo);
+    else
+      OS << "NULL";
     OS << ")";
   } else
     OS << "UNDEFINED";

[maksfb]

LGTM. Thanks.