Hello, Short Question: I have a question about how GCC flushes register values to memory in locks. Long Question: I am implementing hardware transactional memory system and I need my code to touch every read and write set between two code points. As far as I know, GCC automatically detects lock start and lock end so it reads data freshly from the memory and flush everything before lock end. I do not need the actual spin lock but I need GCC's fresh read and flush write mechanism on hardware transactional memory program compilation. In fact, I cannot use any system calls for this solution because my hardware simulator won't accept system calls. So please answer my question without using system calls. Problem: Let's consider following simple lock program. // example1.c LOCK(&mutex); g_var++; UNLOCK(&mutex); As far as I know, GCC would read fresh value of g_var and flush down g_var to the memory before UNLOCK(). Now I have this hardware transactional memory program. // example2.c TM_BEGIN(); g_var++; TM_END(); Those TM_BEGIN() and TM_END() macros are nothing but reserved assembly instruction telling the hardware to isolate and atomicize accesses between TM_BEGIN() and TM_END(). The problem is that GCC doesn't recognize the critical section as critical section and it does not read fresh nor flush before TM_END(). I could have used volatile keyword on g_var. But this next example would be disaster for volatile-based code. // example3.c TM_BEGIN(); for (int i = 0; i < 1000*1000; i++) g_var++; TM_END(); Doesn't this mean 1 million memory access instead of 1 memory read and 1 memory write at the end? I could have coded in assembly myself to force this fresh read and flush on exit, but there are so many code lines to deal with. Also, I could have used optimization level -O1 or lower to not worry about this, but the code becomes so slow and it's not the optimization people will use for the real software. So having GCC's read fresh and flush on exit as a separate function or macro is critical on my research. I tried searching, but I don't know how you call these features so searching didn't help me much. Could you help me on this? Thanks for reading this email and thanks in advance. -- View this message in context: http://www.nabble.com/Question-about-flushing-registers-to-memory-in-locks-tp25613161p25613161.html Sent from the gcc - Help mailing list archive at Nabble.com.
