Reland 877a9f9abec61f06e39f1cd872e37b828139c2d1 since D138654 (parent)
has been fixed with 9ebaf4fef4aac89d4eff08e48185d61bc893f14e and with
8f1e11c5a7d70f96943a72649daa69f152d73e90.
Differential Revision: https://reviews.llvm.org/D126455
This reverts commit 877a9f9abec61f06e39f1cd872e37b828139c2d1.
It depends on the parent revision 42c2dc401742266da3e0251b6c1ca491f4779963
which needs to be reverted as it broke some buildbots, so reverting both.
The aim of this patch is to minimize the compilation time overhead of
running Function Specialization. It is about 40% slower to run as a
standalone pass (IPSCCP + FuncSpec vs IPSCCP with FuncSpec) according
to my measurements. I compiled the llvm testsuite with NewPM-O3 + LTO
and measured single threaded [user + system] time of IPSCCP and FuncSpec
by passing the '-time-passes' option to lld. Then I compared the two
configurations in terms of Instruction Count of the total compilation
(not of the individual passes) as in https://llvm-compile-time-tracker.com.
Geomean for non-LTO builds is -0.25% and LTO is -0.5% approximately.
You can find more info below:
https://discourse.llvm.org/t/rfc-should-we-enable-function-specialization/61518
Differential Revision: https://reviews.llvm.org/D126455
[fixed test to work with reverse iteration]
The `FunctionSpecialization` pass has support for specialising
functions, which are called with literal arguments. This functionality
is disabled by default and is enabled with the option
`-function-specialization-for-literal-constant` . There are a few
issues with the implementation, though:
* even with the default, the pass will still specialise based on
floating-point literals
* even when it's enabled, the pass will specialise only for the `i1`
type (or `i2` if all of the possible 4 values occur, or `i3` if all
of the possible 8 values occur, etc)
The reason for this is incorrect check of the lattice value of the
function formal parameter. The lattice value is `overdefined` when the
constant range of the possible arguments is the full set, and this is
the reason for the specialisation to trigger. However, if the set of
the possible arguments is not the full set, that must not prevent the
specialisation.
This patch changes the pass to NOT consider a formal parameter when
specialising a function if the lattice value for that parameter is:
* unknown or undef
* a constant
* a constant range with a single element
on the basis that specialisation is pointless for those cases.
Is also changes the criteria for picking up an actual argument to
specialise if the argument is:
* a LLVM IR constant
* has `constant` lattice value
has `constantrange` lattice value with a single element.
Reviewed By: ChuanqiXu
Differential Revision: https://reviews.llvm.org/D135893
Change-Id: Iea273423176082ec51339aa66a5fe9fea83557ee
The `FunctionSpecialization` pass has support for specialising
functions, which are called with literal arguments. This functionality
is disabled by default and is enabled with the option
`-function-specialization-for-literal-constant` . There are a few
issues with the implementation, though:
* even with the default, the pass will still specialise based on
floating-point literals
* even when it's enabled, the pass will specialise only for the `i1`
type (or `i2` if all of the possible 4 values occur, or `i3` if all
of the possible 8 values occur, etc)
The reason for this is incorrect check of the lattice value of the
function formal parameter. The lattice value is `overdefined` when the
constant range of the possible arguments is the full set, and this is
the reason for the specialisation to trigger. However, if the set of
the possible arguments is not the full set, that must not prevent the
specialisation.
This patch changes the pass to NOT consider a formal parameter when
specialising a function if the lattice value for that parameter is:
* unknown or undef
* a constant
* a constant range with a single element
on the basis that specialisation is pointless for those cases.
Is also changes the criteria for picking up an actual argument to
specialise if the argument is:
* a LLVM IR constant
* has `constant` lattice value
has `constantrange` lattice value with a single element.
Reviewed By: ChuanqiXu
Differential Revision: https://reviews.llvm.org/D135893
