Vanderson Martins do Rosario <vanderson...@gmail.com> writes:
> Hi everyone, > > I’m sending this email to present myself and a project that I’m planning to > submit to QEMU/GSoC this year. As I see that this project could result in > useful improvements and tools to the community, I would love to have > feedback from the community and perhaps make it even more useful. > <snip> > > Project: Improving Measurement of Tiny Code Generation Quality. > Mentor: Alex Bennée > > I/ Introduction > > In most applications, the majority of the execution time is spent in a very > small portion of code. Regions of a code which have high-frequency > execution are called hot while all other regions are called cold. As a > direct consequence, emulators also spent most of their execution time > emulating these hot regions and, so, dynamic compilers and translators need > to pay extra attention to them. To guarantee that these hot regions are > compiled/translated generating high-quality code is fundamental to achieve > a final high-performance emulation. Thus, one of the most important steps > in tuning an emulator performance is to identify which are the hot regions > and to measure their translation quality. > > QEMU is not different and it offers the ‘-d’ options which can dump the > imputed assembly (guest binary) with ‘-d in_asm’, the generated TCG > Intermediate Representation (IR, TCG ops) with ‘-d op_opt‘ and the final > host assembly (target binary) with ‘-d out_asm’. We actually have two stages: -d op These are the TCG ops as generated while decoding instructions. Some of the higher level generators may generate different sequences if they can detect a simple optimisation. For example tcg_gen_addi_i32 will fold an addi reg,#0 to a simple move. -d op_opt These are the TCG ops after the optimisation pass (tcg_optimize). This is where the code generator will attempt to improve the code for the whole block by propagating constants and copies and folding constant expressions. -- Alex Bennée
