[llvm] [BOLT][NFC] Use brstack in guides and user outputs (PR #163950)

[Amir Ayupov via llvm-commits]

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@@ -5,7 +5,7 @@
 
 Many Linux applications spend a significant amount of their execution time in the kernel. Thus, when we consider code optimization for system performance, it is essential to improve the CPU utilization not only in the user-space applications and libraries but also in the kernel. BOLT has demonstrated double-digit gains while being applied to user-space programs. This guide shows how to apply BOLT to the x86-64 Linux kernel and enhance your system's performance. In our experiments, BOLT boosted database TPS by 2 percent when applied to the kernel compiled with the highest level optimizations, including PGO and LTO. The database spent ~40% of the time in the kernel and was quite sensitive to kernel performance.
 
-BOLT optimizes code layout based on a low-level execution profile collected with the Linux `perf` tool. The best quality profile should include branch history, such as Intel's last branch records (LBR). BOLT runs on a linked binary and reorders the code while combining frequently executed blocks of instructions in a manner best suited for the hardware. Other than branch instructions, most of the code is left unchanged. Additionally, BOLT updates all metadata associated with the modified code, including DWARF debug information and Linux ORC unwind information.
+BOLT optimizes code layout based on a low-level execution profile collected with the Linux `perf` tool. The best quality profile should include branch stack history (brstack), such as Intel's last branch records (LBR) or AArch64's Branch Record Buffer Extension (BRBE). BOLT runs on a linked binary and reorders the code while combining frequently executed blocks of instructions in a manner best suited for the hardware. Other than branch instructions, most of the code is left unchanged. Additionally, BOLT updates all metadata associated with the modified code, including DWARF debug information and Linux ORC unwind information.
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aaupov wrote:

```suggestion
BOLT optimizes code layout based on a low-level execution profile collected with the Linux `perf` tool. The best quality profile should include branch history (brstack), such as Intel's last branch records (LBR) or AArch64's Branch Record Buffer Extension (BRBE). BOLT runs on a linked binary and reorders the code while combining frequently executed blocks of instructions in a manner best suited for the hardware. Other than branch instructions, most of the code is left unchanged. Additionally, BOLT updates all metadata associated with the modified code, including DWARF debug information and Linux ORC unwind information.
```

https://github.com/llvm/llvm-project/pull/163950