Pdf issues I found

[jsjtxietian]

Hi thanks for the great work!

Here are some issues I found when reading the pdf version of this excellent book:

• Low resolution Figure 5.5, The roofline performance model has low resolution and thus a little blur, see the screenshot of the official pdf:

• This link in Chap11 PGO is outdated: https://github.com/google/llvm-propeller/blob/plo-dev/Propeller_RFC.pdf
• This Image covered the line above as shown below:

• The link https://sites.google.com/site/intelptmicrotutorial/ is outdated, but web archive has it saved.

[dendibakh]

Thanks for reporting! I fixed them. Will add them to the errata and push it to the printed version as well. There are a few other low-res images I fixed.