c = pMem->flags;
sqlite3VdbeMemRelease(pMem);
pMem->flags = MEM_Str|MEM_Term|(c&(MEM_AffMask|MEM_Subtype));
[1]https://github.com/smparkes/sqlite/blob/8caf9219240123fbe6cf...
from the post by Dr. Richard Hipp "From the -S output, it looks like Clang-11.0.0 is compiling these three lines as if there were written as:"
sqlite3VdbeMemRelease(pMem);
pMem->flags = MEM_Str|MEM_Term|(pMem->flags&(MEM_AffMask|MEM_Subtype));>> Clang seems to be assuming that the sqlite3VdbeMemRelease() function does not change the value of pMem->flags.
But for some reason, it's thinking it can just reread the flags from the structure after that function, which has a non-const pointer
void sqlite3VdbeMemRelease(Mem *p);
I'll be waiting for the excuses of the "C standard evangelists" and the extreme optimization people on how the SQLite developers are wrong on this case and how it's funny to pull the rug under them.
The pointer being const would not give the compiler any more guarantees that would allow it to reorder the read.
[edit] I see what you're asking. The point is that the compiler changes:
c = pMem->flags;
sqlite3VdbeMemRelease(pMem);
sqlite3VdbeMemRelease(pMem);
c = pMem->flags;