Merge commit 'b385428e3d' into subtree-update_cg_gcc_2024-03-05

compiler/rustc_codegen_gcc/doc/debugging-gcc-lto.md

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+# How to debug GCC LTO
+
+Run do the command with `-v -save-temps` and then extract the `lto1` line from the output and run that under the debugger.

compiler/rustc_codegen_gcc/doc/debugging-libgccjit.md

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+# Debugging libgccjit
+
+Sometimes, libgccjit will crash and output an error like this:
+
+```
+during RTL pass: expand
+libgccjit.so: error: in expmed_mode_index, at expmed.h:249
+0x7f0da2e61a35 expmed_mode_index
+	../../../gcc/gcc/expmed.h:249
+0x7f0da2e61aa4 expmed_op_cost_ptr
+	../../../gcc/gcc/expmed.h:271
+0x7f0da2e620dc sdiv_cost_ptr
+	../../../gcc/gcc/expmed.h:540
+0x7f0da2e62129 sdiv_cost
+	../../../gcc/gcc/expmed.h:558
+0x7f0da2e73c12 expand_divmod(int, tree_code, machine_mode, rtx_def*, rtx_def*, rtx_def*, int)
+	../../../gcc/gcc/expmed.c:4335
+0x7f0da2ea1423 expand_expr_real_2(separate_ops*, rtx_def*, machine_mode, expand_modifier)
+	../../../gcc/gcc/expr.c:9240
+0x7f0da2cd1a1e expand_gimple_stmt_1
+	../../../gcc/gcc/cfgexpand.c:3796
+0x7f0da2cd1c30 expand_gimple_stmt
+	../../../gcc/gcc/cfgexpand.c:3857
+0x7f0da2cd90a9 expand_gimple_basic_block
+	../../../gcc/gcc/cfgexpand.c:5898
+0x7f0da2cdade8 execute
+	../../../gcc/gcc/cfgexpand.c:6582
+```
+
+To see the code which causes this error, call the following function:
+
+```c
+gcc_jit_context_dump_to_file(ctxt, "/tmp/output.c", 1 /* update_locations */)
+```
+
+This will create a C-like file and add the locations into the IR pointing to this C file.
+Then, rerun the program and it will output the location in the second line:
+
+```
+libgccjit.so: /tmp/something.c:61322:0: error: in expmed_mode_index, at expmed.h:249
+```
+
+Or add a breakpoint to `add_error` in gdb and print the line number using:
+
+```
+p loc->m_line
+p loc->m_filename->m_buffer
+```
+
+To print a debug representation of a tree:
+
+```c
+debug_tree(expr);
+```
+
+(defined in print-tree.h)
+
+To print a debug representation of a gimple struct:
+
+```c
+debug_gimple_stmt(gimple_struct)
+```
+
+To get the `rustc` command to run in `gdb`, add the `--verbose` flag to `cargo build`.
+
+To have the correct file paths in `gdb` instead of `/usr/src/debug/gcc/libstdc++-v3/libsupc++/eh_personality.cc`:
+
+Maybe by calling the following at the beginning of gdb:
+
+```
+set substitute-path /usr/src/debug/gcc /path/to/gcc-repo/gcc
+```
+
+TODO(antoyo): but that's not what I remember I was doing.

compiler/rustc_codegen_gcc/doc/errors.md

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+# Common errors
+
+This file lists errors that were encountered and how to fix them.
+
+### `failed to build archive` error
+
+When you get this error:
+
+```
+error: failed to build archive: failed to open object file: No such file or directory (os error 2)
+```
+
+That can be caused by the fact that you try to compile with `lto = "fat"`, but you didn't compile the sysroot with LTO.
+(Not sure if that's the reason since I cannot reproduce anymore. Maybe it happened when forgetting setting `FAT_LTO`.)
+
+### ld: cannot find crtbegin.o
+
+When compiling an executable with libgccijt, if setting the `*LIBRARY_PATH` variables to the install directory, you will get the following errors:
+
+```
+ld: cannot find crtbegin.o: No such file or directory
+ld: cannot find -lgcc: No such file or directory
+ld: cannot find -lgcc: No such file or directory
+libgccjit.so: error: error invoking gcc driver
+```
+
+To fix this, set the variables to `gcc-build/build/gcc`.

compiler/rustc_codegen_gcc/doc/subtree.md

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+# git subtree sync
+
+`rustc_codegen_gcc` is a subtree of the rust compiler. As such, it needs to be
+sync from time to time to ensure changes that happened on their side are also
+included on our side.
+
+### How to install a forked git-subtree
+
+Using git-subtree with `rustc` requires a patched git to make it work.
+The PR that is needed is [here](https://github.com/gitgitgadget/git/pull/493).
+Use the following instructions to install it:
+
+```bash
+git clone git@github.com:tqc/git.git
+cd git
+git checkout tqc/subtree
+make
+make install
+cd contrib/subtree
+make
+cp git-subtree ~/bin
+```
+
+### Syncing with rust compiler
+
+Do a sync with this command:
+
+```bash
+PATH="$HOME/bin:$PATH" ~/bin/git-subtree push -P compiler/rustc_codegen_gcc/ ../rustc_codegen_gcc/ sync_branch_name
+cd ../rustc_codegen_gcc
+git checkout master
+git pull
+git checkout sync_branch_name
+git merge master
+```
+
+To send the changes to the rust repo:
+
+```bash
+cd ../rust
+git pull origin master
+git checkout -b subtree-update_cg_gcc_YYYY-MM-DD
+PATH="$HOME/bin:$PATH" ~/bin/git-subtree pull --prefix=compiler/rustc_codegen_gcc/ https://github.com/rust-lang/rustc_codegen_gcc.git master
+git push
+
+# Immediately merge the merge commit into cg_gcc to prevent merge conflicts when syncing from rust-lang/rust later.
+PATH="$HOME/bin:$PATH" ~/bin/git-subtree push -P compiler/rustc_codegen_gcc/ ../rustc_codegen_gcc/ sync_branch_name
+```
+
+TODO: write a script that does the above.
+
+https://rust-lang.zulipchat.com/#narrow/stream/301329-t-devtools/topic/subtree.20madness/near/258877725

compiler/rustc_codegen_gcc/doc/tips.md

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+# Tips
+
+The following shows how to do different random small things we encountered and thought could
+be useful.
+
+### How to send arguments to the GCC linker
+
+```
+CG_RUSTFLAGS="-Clink-args=-save-temps -v" ../y.sh cargo build
+```
+
+### How to see the personality functions in the asm dump
+
+```
+CG_RUSTFLAGS="-Clink-arg=-save-temps -v -Clink-arg=-dA" ../y.sh cargo build
+```
+
+### How to see the LLVM IR for a sysroot crate
+
+```
+cargo build -v --target x86_64-unknown-linux-gnu -Zbuild-std
+# Take the command from the output and add --emit=llvm-ir
+```
+
+### To prevent the linker from unmangling symbols
+
+Run with:
+
+```
+COLLECT_NO_DEMANGLE=1
+```
+
+### How to use a custom-build rustc
+
+ * Build the stage2 compiler (`rustup toolchain link debug-current build/x86_64-unknown-linux-gnu/stage2`).
+ * Clean and rebuild the codegen with `debug-current` in the file `rust-toolchain`.
+
+### How to use [mem-trace](https://github.com/antoyo/mem-trace)
+
+`rustc` needs to be built without `jemalloc` so that `mem-trace` can overload `malloc` since `jemalloc` is linked statically, so a `LD_PRELOAD`-ed library won't a chance to intercept the calls to `malloc`.
+
+### How to generate GIMPLE
+
+If you need to check what gccjit is generating (GIMPLE), then take a look at how to
+generate it in [gimple.md](./doc/gimple.md).
+
+### How to build a cross-compiling libgccjit
+
+#### Building libgccjit
+
+ * Follow the instructions on [this repo](https://github.com/cross-cg-gcc-tools/cross-gcc).
+
+#### Configuring rustc_codegen_gcc
+
+ * Run `./y.sh prepare --cross` so that the sysroot is patched for the cross-compiling case.
+ * Set the path to the cross-compiling libgccjit in `gcc-path` (in `config.toml`).
+ * Make sure you have the linker for your target (for instance `m68k-unknown-linux-gnu-gcc`) in your `$PATH`. Currently, the linker name is hardcoded as being `$TARGET-gcc`. Specify the target when building the sysroot: `./y.sh build --target-triple m68k-unknown-linux-gnu`.
+ * Build your project by specifying the target: `OVERWRITE_TARGET_TRIPLE=m68k-unknown-linux-gnu ../y.sh cargo build --target m68k-unknown-linux-gnu`.
+
+If the target is not yet supported by the Rust compiler, create a [target specification file](https://docs.rust-embedded.org/embedonomicon/custom-target.html) (note that the `arch` specified in this file must be supported by the rust compiler).
+Then, you can use it the following way:
+
+ * Add the target specification file using `--target` as an **absolute** path to build the sysroot: `./y.sh build --target-triple m68k-unknown-linux-gnu --target $(pwd)/m68k-unknown-linux-gnu.json`
+ * Build your project by specifying the target specification file: `OVERWRITE_TARGET_TRIPLE=m68k-unknown-linux-gnu ../y.sh cargo build --target path/to/m68k-unknown-linux-gnu.json`.
+
+If you get the following error:
+
+```
+/usr/bin/ld: unrecognised emulation mode: m68kelf
+```
+
+Make sure you set `gcc-path` (in `config.toml`) to the install directory.