[PATCH] D131337: Wrap `llvm_unreachable` macro in do-while loop

[Stefan Gränitz via Phabricator via llvm-commits]

sgraenitz created this revision.
sgraenitz added reviewers: mehdi_amini, dexonsmith, lhames.
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Macros that expand into multiple terms can cause interesting preprocessor hickups depending 
on the context they are used in. https://github.com/llvm/llvm-project/issues/56867 reported 
a miscompilation of `llvm_unreachable(msg)` inside a `LLVM_DEBUG({ ... })` block. We were 
able to fix it by wrapping the expansion in a `do {} while(false)`.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D131337

Files:
  llvm/include/llvm/Support/ErrorHandling.h


Index: llvm/include/llvm/Support/ErrorHandling.h
===================================================================
--- llvm/include/llvm/Support/ErrorHandling.h
+++ llvm/include/llvm/Support/ErrorHandling.h
@@ -147,7 +147,9 @@
 #elif LLVM_UNREACHABLE_OPTIMIZE
 #define llvm_unreachable(msg) LLVM_BUILTIN_UNREACHABLE
 #else
-#define llvm_unreachable(msg) LLVM_BUILTIN_TRAP, LLVM_BUILTIN_UNREACHABLE
+#define llvm_unreachable(msg) \
+  do { LLVM_BUILTIN_TRAP; LLVM_BUILTIN_UNREACHABLE; \
+  } while (false)
 #endif
 
 #endif


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