[PATCH] D101217: Add LLVM_ATTRIBUTE_USED to fix problems which could be exposed by aggressive global pointer variable removal

[Fangrui Song via Phabricator via llvm-commits]

MaskRay created this revision.
MaskRay added reviewers: evgeny777, jyknight, lattner, reames, saugustine.
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Note to BuryPointer.cpp:GraveYard. 'unused' cannot prevent (1) dead store
elimination and (2) removal of the global pointer variable (D69428 <https://reviews.llvm.org/D69428>) but 'used' can.

Discovered when comparing link maps between HEAD+D69428 <https://reviews.llvm.org/D69428> and HEAD.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D101217

Files:
  llvm/lib/Support/BuryPointer.cpp
  llvm/lib/Support/Unix/Signals.inc


Index: llvm/lib/Support/Unix/Signals.inc
===================================================================
--- llvm/lib/Support/Unix/Signals.inc
+++ llvm/lib/Support/Unix/Signals.inc
@@ -255,7 +255,7 @@
 // stack if we remove our signal handlers; that can't be done reliably if
 // someone else is also trying to do the same thing.
 static stack_t OldAltStack;
-static void* NewAltStackPointer;
+LLVM_ATTRIBUTE_USED static void *NewAltStackPointer;
 
 static void CreateSigAltStack() {
   const size_t AltStackSize = MINSIGSTKSZ + 64 * 1024;
Index: llvm/lib/Support/BuryPointer.cpp
===================================================================
--- llvm/lib/Support/BuryPointer.cpp
+++ llvm/lib/Support/BuryPointer.cpp
@@ -19,7 +19,7 @@
   // will not be properly buried and a leak detector will report a leak, which
   // is what we want in such case.
   static const size_t kGraveYardMaxSize = 16;
-  LLVM_ATTRIBUTE_UNUSED static const void *GraveYard[kGraveYardMaxSize];
+  LLVM_ATTRIBUTE_USED static const void *GraveYard[kGraveYardMaxSize];
   static std::atomic<unsigned> GraveYardSize;
   unsigned Idx = GraveYardSize++;
   if (Idx >= kGraveYardMaxSize)


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