Thread.InitializeCurrentThread should be marked as cold code #49520
Description
Thread.InitializeCurrentThread is only called once for the Thread lifetime, however the method it is used in CurrentThread is called lots and every async method has its own call to it (to get ExecutionContext etc)
runtime/src/libraries/System.Private.CoreLib/src/System/Threading/Thread.cs
Lines 328 to 335 in bdd6d35
Currently the asm generated is a conditional jmp forward for it already being set e.g. from AsyncMethodBuilderCore:Start(byref) which is bad for static branch prediction.
G_M49992_IG03:
call [CORINFO_HELP_READYTORUN_STATIC_BASE]
mov rax, gword ptr [rax+24]
test rax, rax
jne SHORT G_M49992_IG05
;; bbWeight=1 PerfScore 6.25
G_M49992_IG04:
call [Thread:InitializeCurrentThread():Thread]
;; bbWeight=0.25 PerfScore 0.75
G_M49992_IG05:
mov ...Reversing the condition in CurrentThread
Thread? currentThread = t_currentThread;
if (currentThread is not null)
{
return currentThread;
}
return InitializeCurrentThread();While it generates a conditional jmp forward for InitializeCurrentThread it also then adds a jmp for the regular path:
G_M49992_IG03:
call [CORINFO_HELP_READYTORUN_STATIC_BASE]
mov rax, gword ptr [rax+24]
test rax, rax
je SHORT G_M49992_IG05
;; bbWeight=1 PerfScore 6.25
G_M49992_IG04:
jmp SHORT G_M49992_IG06
;; bbWeight=0.50 PerfScore 1.00
G_M49992_IG05:
call [Thread:InitializeCurrentThread():Thread]
;; bbWeight=0.50 PerfScore 1.50
G_M49992_IG06:
mov ...Marking it as a cold method should resolve this by moving the call to InitializeCurrentThread to the end of the method so the regular path didn't have to jump over it?
/cc @EgorBo
category:performance
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