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112 lines
3.1 KiB
Markdown
112 lines
3.1 KiB
Markdown
# GIMPLE
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You can see the full documentation about what GIMPLE is [here](https://gcc.gnu.org/onlinedocs/gccint/GIMPLE.html). In this document we will explain how to generate it.
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First, we'll copy the content from `gcc/gcc/testsuite/jit.dg/test-const-attribute.c` into a
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file named `local.c` and remove the content we're not interested into:
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```diff
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- /* { dg-do compile { target x86_64-*-* } } */
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...
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- /* We don't want set_options() in harness.h to set -O3 to see that the const
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- attribute affects the optimizations. */
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- #define TEST_ESCHEWS_SET_OPTIONS
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- static void set_options (gcc_jit_context *ctxt, const char *argv0)
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- {
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- // Set "-O3".
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- gcc_jit_context_set_int_option(ctxt, GCC_JIT_INT_OPTION_OPTIMIZATION_LEVEL, 3);
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- }
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-
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- #define TEST_COMPILING_TO_FILE
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- #define OUTPUT_KIND GCC_JIT_OUTPUT_KIND_ASSEMBLER
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- #define OUTPUT_FILENAME "output-of-test-const-attribute.c.s"
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- #include "harness.h"
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...
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- /* { dg-final { jit-verify-output-file-was-created "" } } */
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- /* Check that the loop was optimized away */
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- /* { dg-final { jit-verify-assembler-output-not "jne" } } */
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```
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Then we'll add a `main` function which will call the `create_code` function but
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also add the calls we need to generate the GIMPLE:
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```C
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int main() {
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gcc_jit_context *ctxt = gcc_jit_context_acquire();
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// To set `-O3`, update it depending on your needs.
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gcc_jit_context_set_int_option(ctxt, GCC_JIT_INT_OPTION_OPTIMIZATION_LEVEL, 3);
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// Very important option to generate the gimple format.
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gcc_jit_context_set_bool_option(ctxt, GCC_JIT_BOOL_OPTION_DUMP_INITIAL_GIMPLE, 1);
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create_code(ctxt, NULL);
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gcc_jit_context_compile(ctxt);
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// If you want to compile to assembly (or any other format) directly, you can
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// use the following call instead:
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// gcc_jit_context_compile_to_file(ctxt, GCC_JIT_OUTPUT_KIND_ASSEMBLER, "out.s");
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return 0;
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}
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```
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Then we can compile it by using:
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```console
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gcc local.c -I `pwd`/gcc/gcc/jit/ -L `pwd`/gcc-build/gcc -lgccjit -o out
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```
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And finally when you run it:
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```console
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LD_LIBRARY_PATH=`pwd`/gcc-build/gcc LIBRARY_PATH=`pwd`/gcc-build/gcc ./out
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```
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It should display:
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```c
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__attribute__((const))
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int xxx ()
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{
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int D.3394;
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int sum;
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int x;
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<D.3377>:
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x = 45;
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sum = 0;
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goto loop_cond;
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loop_cond:
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x = x >> 1;
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if (x != 0) goto after_loop; else goto loop_body;
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loop_body:
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_1 = foo (x);
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_2 = _1 * 2;
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x = x + _2;
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goto loop_cond;
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after_loop:
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D.3394 = sum;
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return D.3394;
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}
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```
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An alternative way to generate the GIMPLE is to replace:
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```c
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gcc_jit_context_set_bool_option(ctxt, GCC_JIT_BOOL_OPTION_DUMP_INITIAL_GIMPLE, 1);
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```
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with:
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```c
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gcc_jit_context_add_command_line_option(ctxt, "-fdump-tree-gimple");
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```
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(although you can have both at the same time too). Then you can compile it like previously. Only one difference: before executing it, I recommend to run:
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```console
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rm -rf /tmp/libgccjit-*
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```
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to make it easier for you to know which folder to look into.
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Once the execution is done, you should now have a file with path looking like `/tmp/libgccjit-9OFqkD/fake.c.006t.gimple` which contains the GIMPLE format.
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