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Peter Zijlstra noticed that with CONFIG_PROFILE_ALL_BRANCHES, the "if" macro converts the conditional to an array index. This can cause GCC to create horrible code. When there are nested ifs, the generated code uses register values to encode branching decisions. Josh Poimboeuf found that replacing the define "if" macro from using the condition as an array index and incrementing the branch statics with an if statement itself, reduced the asm complexity and shrinks the generated code quite a bit. But this can be simplified even further by replacing the internal if statement with a ternary operator. Link: https://lkml.kernel.org/r/20190307174802.46fmpysxyo35hh43@treble Link: http://lkml.kernel.org/r/CAHk-=wiALN3jRuzARpwThN62iKd476Xj-uom+YnLZ4=eqcz7xQ@mail.gmail.com Reported-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reported-by: Josh Poimboeuf <jpoimboe@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.