Merge pull request #16309 from JuliaLang/yyc/threads/signal_fence

Use inlineasm as signal fence on ARM and AArch64

src/cgutils.cpp

@@ -1762,10 +1762,19 @@ static Value *emit_exc_in_transit(jl_codectx_t *ctx)
 
 static void emit_signal_fence(void)
 {
-#ifdef LLVM39
- builder.CreateFence(AtomicOrdering::SequentiallyConsistent, SingleThread);
+#if defined(_CPU_ARM_) || defined(_CPU_AARCH64_)
+ // LLVM generates very inefficient code (and might include function call)
+ // for signal fence. Fallback to the poor man signal fence with
+ // inline asm instead.
+ // https://llvm.org/bugs/show_bug.cgi?id=27545
+ builder.CreateCall(InlineAsm::get(FunctionType::get(T_void, false), "",
+ "~{memory}", true));
 #else
+# ifdef LLVM39
+ builder.CreateFence(AtomicOrdering::SequentiallyConsistent, SingleThread);
+# else
  builder.CreateFence(SequentiallyConsistent, SingleThread);
+# endif
 #endif
 }
 

src/codegen.cpp

@@ -102,6 +102,9 @@
 #include <llvm/ExecutionEngine/JITMemoryManager.h>
 #include <llvm/ExecutionEngine/Interpreter.h>
 #endif
+#if defined(_CPU_ARM_) || defined(_CPU_AARCH64_)
+# include <llvm/IR/InlineAsm.h>
+#endif
 
 using namespace llvm;