*: Fix build and readme in llvm17 (#9656)

ref #6233

Fix README instruction for MacOS
Fix build unit test failure in LLVM17 + MacOS

Signed-off-by: Wish <[email protected]>

Co-authored-by: ti-chi-bot[bot] <108142056+ti-chi-bot[bot]@users.noreply.github.com>
Co-authored-by: JaySon <[email protected]>
Co-authored-by: Liqi Geng <[email protected]>

README.md

@@ -65,6 +65,13 @@ sudo ./llvm.sh 17 all
 sudo apt install -y cmake ninja-build zlib1g-dev libcurl4-openssl-dev ccache
 ```
 
+Then, expose the LLVM17 toolchain as the default one in order to use it later in compile:
+
+```shell
+export CC="/usr/bin/clang-17"
+export CXX="/usr/bin/clang++-17"
+```
+
 **Note for Ubuntu 18.04 and Ubuntu 20.04:**
 
 The default installed cmake may be not recent enough. You can install a newer cmake from the [Kitware APT Repository](https://apt.kitware.com):
@@ -125,9 +132,14 @@ xcode-select --install
 brew install ninja cmake [email protected] ccache
 
 brew install llvm@17
+```
+
+Then, expose the LLVM17 toolchain as the default one in order to use it later in compile:
 
-# check llvm version
-clang --version # should be 17.0.0 or higher
+```shell
+export PATH="$(brew --prefix)/opt/llvm@17/bin:$PATH"
+export CC="$(brew --prefix)/opt/llvm@17/bin/clang"
+export CXX="$(brew --prefix)/opt/llvm@17/bin/clang++"
 ```
 
 </details>
@@ -148,34 +160,16 @@ To build TiFlash for development:
 cmake --workflow --preset dev
 ```
 
-Note: In Linux, usually you need to explicitly specify to use LLVM.
-
-```shell
-export CC="/usr/bin/clang-17"
-export CXX="/usr/bin/clang++-17"
-```
-
-In MacOS, if you install llvm clang, you need to explicitly specify to use llvm clang.
+Or if you don't like the preset:
 
-Add the following lines to your shell environment, e.g. `~/.bash_profile`.
-```shell
-export PATH="$(brew --prefix)/opt/llvm/bin:$PATH"
-export CC="$(brew --prefix)/opt/llvm/bin/clang"
-export CXX="$(brew --prefix)/opt/llvm/bin/clang++"
-```
-
-Or use `CMAKE_C_COMPILER` and `CMAKE_CXX_COMPILER` to specify the compiler, like this:
 ```shell
+# In the TiFlash repository root:
 mkdir cmake-build-debug
 cd cmake-build-debug
-
-cmake .. -GNinja -DCMAKE_BUILD_TYPE=DEBUG -DCMAKE_C_COMPILER="$(brew --prefix)/opt/llvm/bin/clang" -DCMAKE_CXX_COMPILER="$(brew --prefix)/opt/llvm/bin/clang++"
-
+cmake .. -GNinja -DCMAKE_BUILD_TYPE=DEBUG
 ninja tiflash
 ```
 
-After building, you can get TiFlash binary in `dbms/src/Server/tiflash` in the `cmake-build-debug` directory.
-
 ### Build Options
 
 TiFlash has several CMake build options to tweak for development purposes. These options SHOULD NOT be changed for production usage, as they may introduce unexpected build errors and unpredictable runtime behaviors.

dbms/src/Storages/DeltaMerge/tests/gtest_segment_bitmap.cpp

@@ -125,7 +125,7 @@ class SegmentBitmapFilterTest : public SegmentTestBasic
             SegmentTestBasic::writeSegment(SEG_ID, end - begin, begin);
             if (unit.pack_size)
             {
-                db_context->getSettingsRef().set("dt_segment_stable_pack_rows", *(unit.pack_size));
+                db_context->getSettingsRef().dt_segment_stable_pack_rows = *(unit.pack_size);
                 reloadDMContext();
                 ASSERT_EQ(dm_context->stable_pack_rows, *(unit.pack_size));
             }