The pass used to be enabled by default with CodeGenOpt::Less (-O1).
This is too aggressive, considering the pass indiscriminately merges
all globals together.
Currently, performance doesn't always improve, and, on code that uses
few globals (e.g., the odd file- or function- static), more often than
not is degraded by the optimization. Lengthy discussion can be found
on llvmdev (AArch64-focused; ARM has similar problems):
http://lists.cs.uiuc.edu/pipermail/llvmdev/2015-February/082800.html
Also, it makes tooling and debuggers less useful when dealing with
globals and data sections.
GlobalMerge needs to better identify those cases that benefit, and this
will be done separately. In the meantime, move the pass to run with
-O3 rather than -O1, on both ARM and AArch64.
llvm-svn: 233024
A global variable without an explicit alignment specified should be assumed to
be ABI-aligned according to its type, like on other platforms. This allows us
to use better memory operations when accessing it.
rdar://18533701
llvm-svn: 223180
This patch is to move GlobalMerge pass from Transform/Scalar
to CodeGen, because GlobalMerge depends on TargetMachine.
In the mean time, the macro INITIALIZE_TM_PASS is also moved
to CodeGen/Passes.h. With this fix we can avoid making
libScalarOpts depend on libCodeGen.
llvm-svn: 210951
Ahmed Bougacha