Hi,
I just wanted to answer myself.
It seems that there are two thresholds that need to be met if a function
is to be specialized within a particular context:
1. --param=hot-bb-count-ws-permille=. This option controls the hotness
threshold of basic blocks and is needed for function specialization
during LTO. If a callsite is not in a hot basic block, it seems that the
callsite will not be specialized for a particular parameter.
2. --param=ipa-cp-eval-threshold=. This option controls a heuristic that
lets constant propagation happen if a function is a good candidate for
cloning. This parameter is used for both: function specialization within
a particular context and for all contexts.
On 10/07/2020 13:19, Erick Ochoa wrote:
Forgot to mention that these functions take a function pointer as a
parameter and as a result, the specialized functions are able to replace
the indirect function call with a direct function call.
On 10/07/2020 13:17, Erick Ochoa wrote:
Hello,
I'm working on an optimization and I encountered this interesting
behaviour. There are a couple of functions that are specialized when
the program is not compiled with PGO (-fprofile-generate and
-fprofile-use)
However, when the program is compiled with PGO the compiler does not
specialize the function calls.
I printing the program just after materializing all clones.
I am running this version of GCC:
Author: GCC Administrator <gccad...@gcc.gnu.org>
Date: Fri Jul 10 00:16:28 2020 +0000
Daily bump.
I can imagine that the profiling information was used to determine
that specializing these functions is a bad tradeoff between binary
size and speed. But I do not know this for sure. How can I find out
why these functions were not specialized? (I.e. is there a threshold
that wasn't met, and if so, where is it located and what's its value?)
Thanks!
