SH4 in Compiler Explorer - Revision history

GyroVorbis: /* Configuration */

2025-08-27T17:31:21Z

Configuration

← Older revision		Revision as of 17:31, 27 August 2025
Line 14:		Line 14:
	* <code>-mfsca</code>: enables emission of the fsca instruction for sine and cosine approximations (not available in GCC 4.7.4)		* <code>-mfsca</code>: enables emission of the fsca instruction for sine and cosine approximations (not available in GCC 4.7.4)
	* <code>-matomic-model=soft-imask</code>: enables support for C11 and C++11 atomics by disabling then reenabling interrupts around atomic variable operations		* <code>-matomic-model=soft-imask</code>: enables support for C11 and C++11 atomics by disabling then reenabling interrupts around atomic variable operations
	* <code>-mtas</code> Backs C11's atomic_flag type by emitting the tas.b instruction, which atomically tests and sets the flag's value, also causing a purge of the cache line it lies within.		* <code>-mtas</code>: Backs C11's atomic_flag type by emitting the tas.b instruction, which atomically tests and sets the flag's value, also causing a purge of the cache line it lies within.
	* <code>-ftls-model=local-exec</code>: enables the model used by KOS for supporting variables declared with the "thread_local" keyword		* <code>-ftls-model=local-exec</code>: enables the model used by KOS for supporting variables declared with the "thread_local" keyword

GyroVorbis: Templates for GCC 15.2.0

2025-08-27T17:30:34Z

Templates for GCC 15.2.0

← Older revision		Revision as of 17:30, 27 August 2025
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	** [https://godbolt.org/z/WWsaaEqWW C23 Hello World]		** [https://godbolt.org/z/WWsaaEqWW C23 Hello World]
	** [https://godbolt.org/z/raP67zWcY C++26 Hello World]		** [https://godbolt.org/z/raP67zWcY C++26 Hello World]
			* GCC 15.2.0
			** [https://godbolt.org/z/TGYr875vs C23 Hello World]
			** [https://godbolt.org/z/7ET55a9sh C++26 Hello World]

	Pre-configured template for ARM GCC8.5, Dreamcast's "AICA" sound chip:		Pre-configured template for ARM GCC8.5, Dreamcast's "AICA" sound chip:

GyroVorbis: Added -mtas flag.

2025-08-27T17:28:06Z

Added -mtas flag.

← Older revision		Revision as of 17:28, 27 August 2025
Line 14:		Line 14:
	* <code>-mfsca</code>: enables emission of the fsca instruction for sine and cosine approximations (not available in GCC 4.7.4)		* <code>-mfsca</code>: enables emission of the fsca instruction for sine and cosine approximations (not available in GCC 4.7.4)
	* <code>-matomic-model=soft-imask</code>: enables support for C11 and C++11 atomics by disabling then reenabling interrupts around atomic variable operations		* <code>-matomic-model=soft-imask</code>: enables support for C11 and C++11 atomics by disabling then reenabling interrupts around atomic variable operations
			* <code>-mtas</code> Backs C11's atomic_flag type by emitting the tas.b instruction, which atomically tests and sets the flag's value, also causing a purge of the cache line it lies within.
	* <code>-ftls-model=local-exec</code>: enables the model used by KOS for supporting variables declared with the "thread_local" keyword		* <code>-ftls-model=local-exec</code>: enables the model used by KOS for supporting variables declared with the "thread_local" keyword

GyroVorbis: Added GCC15.1.0 templates

2025-04-26T14:17:13Z

Added GCC15.1.0 templates

← Older revision		Revision as of 14:17, 26 April 2025
Line 39:		Line 39:
	** [https://godbolt.org/z/a54qTYon4 C23 Hello World]		** [https://godbolt.org/z/a54qTYon4 C23 Hello World]
	** [https://godbolt.org/z/5njMrrh8z C++26 Hello World]		** [https://godbolt.org/z/5njMrrh8z C++26 Hello World]
			* GCC 15.1.0
			** [https://godbolt.org/z/WWsaaEqWW C23 Hello World]
			** [https://godbolt.org/z/raP67zWcY C++26 Hello World]

	Pre-configured template for ARM GCC8.5, Dreamcast's "AICA" sound chip:		Pre-configured template for ARM GCC8.5, Dreamcast's "AICA" sound chip:

GyroVorbis at 15:18, 29 January 2025

2025-01-29T15:18:13Z

@@ Line 7: / Line 7: @@
 * <code>-ml</code>: compile code for the processor in little-endian mode
 * FPU Mode:
 ** <code>-m4-single-only</code>: generate code for the SH4 with a floating-point unit that only supports single-precision floating point arithmetic
 * <code>-ffast-math</code>: breaks strict IEEE compliance and allows for faster floating point approximations
 * <code>-O3</code>: optimization level 3
@@ Line 36: / Line 36: @@
 ** [https://godbolt.org/z/7ha8oj4vd C23 Hello World]
 ** [https://godbolt.org/z/eW8Yd8sG9 C++26 Hello World]
 Pre-configured template for ARM GCC8.5, Dreamcast's "AICA" sound chip:
@@ Line 42: / Line 45: @@
 = Tips and Notes =
 * It has been noted that while <code>-O3</code> is claimed to be the highest optimization level according to recent GCC documentation, some code differences can still be seen under certain circumstances when using <code>-O4</code> and beyond.
-* The compiler seems to ignore both <code>-mfsrra</code> and <code>-mfsca</code> without the <code>-ffast-math</code> and <code>-m4-single-only</code> options.
+* The compiler seems to ignore both <code>-mfsrra</code> and <code>-mfsca</code> without the <code>-ffast-math</code> option.
-* It is highly recommended that C code is written to use <code>-mfsrra</code> (1.0/sqrt(N)) and <code>-mfsca</code> (builtin sin/cos) over using inline assembly directly, as this seems to give the compiler more context for code optimization around these instructions.
+* With the proper flags enabled for fast-math, the compiler is smart enough to leverage the following from pure C code, almost certainly better than you can do with small intrinsic-style inline ASM calls, provided you're using the proper single-precision versions of any <code><math.h></code> routines:
-* The <code>__builtin_prefetch</code> intrinsic does seem to generate a single "pref" instruction and should be preferred over inline assembly.
+**
-* The compiler does not seem smart enough to utilize the FIPR (inner/dot product), FMAC (multiply and accumulate), or FTRV (transform vector) instructions regardless of how embarrassingly vectorizable the supplied C code seems to be, so linear algebra routines are forced to use inline assembly to fully leverage the SH4's SIMD instructions.
+<center>
 * Typically smaller code sizes and more tightly optimized code are seen with newer versions of GCC versus the older ones; however, this is not always the case.
 * Evidently, even without a branch predictor, the C++20 <code><nowiki>[[likely]]</nowiki></code> and <code><nowiki>[[unlikely]]</nowiki></code> attributes as well as the GCC intrinsic <code>__builtin_expect()</code> can have a fairly profound impact on code generation and optimization for conditionals and branches. More information can be found [https://dcemulation.org/phpBB/viewtopic.php?t=106029 here].

GyroVorbis: Created page with "Thanks to the effort of Matt Godbolt (who hilariously enough is a former Dreamcast developer himself), the SuperH GCC toolchain is now available for use with [https://godbolt.org Compiler Explorer], along with all of the SH4-specific compiler flags and options typically used when targeting the Dreamcast. This gives us an invaluable tool for getting quick and immediate feedback on how well a given C or C++ source segment tends to translate into SH4 assembly, offering a li..."

2025-01-08T03:42:00Z

Created page with "Thanks to the effort of Matt Godbolt (who hilariously enough is a former Dreamcast developer himself), the SuperH GCC toolchain is now available for use with [https://godbolt.org Compiler Explorer], along with all of the SH4-specific compiler flags and options typically used when targeting the Dreamcast. This gives us an invaluable tool for getting quick and immediate feedback on how well a given C or C++ source segment tends to translate into SH4 assembly, offering a li..."

New page

Thanks to the effort of Matt Godbolt (who hilariously enough is a former Dreamcast developer himself), the SuperH GCC toolchain is now available for use with [https://godbolt.org Compiler Explorer], along with all of the SH4-specific compiler flags and options typically used when targeting the Dreamcast. This gives us an invaluable tool for getting quick and immediate feedback on how well a given C or C++ source segment tends to translate into SH4 assembly, offering a little sandbox for testing and optimizing code targeting the Dreamcast.

[[File:GCC Compiler Benchmarks.png|thumb|Benchmarking various GCC versions and flags]]

= Configuration =
To arrive at a configuration mirroring a Dreamcast development environment, first select one of the GCC compiler versions for the SH architecture. Secondly, the following compiler options should be used as the baseline configuration:
* <code>-ml</code>: compile code for the processor in little-endian mode
* FPU Mode:
** <code>-m4-single-only</code>: generate code for the SH4 with a floating-point unit that only supports single-precision floating point arithmetic
** <code>-m4-single</code>: generate code for the SH4 with a floating-point unit that supports both single and double-precision floating point arithmetic that defaults to single-precision mode upon function entry
* <code>-ffast-math</code>: breaks strict IEEE compliance and allows for faster floating point approximations
* <code>-O3</code>: optimization level 3
* <code>-mfsrra</code>: enables emission of the fsrra instruction for reciprocal square root approximations (not available in GCC 4.7.4)
* <code>-mfsca</code>: enables emission of the fsca instruction for sine and cosine approximations (not available in GCC 4.7.4)
* <code>-matomic-model=soft-imask</code>: enables support for C11 and C++11 atomics by disabling then reenabling interrupts around atomic variable operations
* <code>-ftls-model=local-exec</code>: enables the model used by KOS for supporting variables declared with the "thread_local" keyword

= Convenience Templates =
The following are pre-configured templates you can use as sample Dreamcast build configurations:
* GCC4.9.4:
** [https://godbolt.org/z/9MKzeMfMj C11 Hello World]
** [https://godbolt.org/z/qGzoeo4sj C++14 Hello World]
* GCC9.5.0:
** [https://godbolt.org/z/rvW3s3594 C17 Hello World]
** [https://godbolt.org/z/qYfE5G6Mx C++17 Hello World]
* GCC12.2.0:
** [https://godbolt.org/z/94TKvxazn C17 Hello World]
** [https://godbolt.org/z/61jqhE3zn C++20 Hello World]
* GCC13.1.0:
** [https://godbolt.org/z/Kb9bKe8ro C2X Hello World]
** [https://godbolt.org/z/51dv4ePsG C++23 Hello World]
* GCC13.2.0:
** [https://godbolt.org/z/rafvMdWGb C2X Hello World]
** [https://godbolt.org/z/MeG3rqna7 C++23 Hello World]
* GCC 14.1.0
** [https://godbolt.org/z/7ha8oj4vd C23 Hello World]
** [https://godbolt.org/z/eW8Yd8sG9 C++26 Hello World]

Pre-configured template for ARM GCC8.5, Dreamcast's "AICA" sound chip:
* [https://godbolt.org/z/895dWG9qf C Hello World]

= Tips and Notes =
* It has been noted that while <code>-O3</code> is claimed to be the highest optimization level according to recent GCC documentation, some code differences can still be seen under certain circumstances when using <code>-O4</code> and beyond.
* The compiler seems to ignore both <code>-mfsrra</code> and <code>-mfsca</code> without the <code>-ffast-math</code> and <code>-m4-single-only</code> options.
* It is highly recommended that C code is written to use <code>-mfsrra</code> (1.0/sqrt(N)) and <code>-mfsca</code> (builtin sin/cos) over using inline assembly directly, as this seems to give the compiler more context for code optimization around these instructions.
* The <code>__builtin_prefetch</code> intrinsic does seem to generate a single "pref" instruction and should be preferred over inline assembly.
* The compiler does not seem smart enough to utilize the FIPR (inner/dot product), FMAC (multiply and accumulate), or FTRV (transform vector) instructions regardless of how embarrassingly vectorizable the supplied C code seems to be, so linear algebra routines are forced to use inline assembly to fully leverage the SH4's SIMD instructions.
* Typically smaller code sizes and more tightly optimized code are seen with newer versions of GCC versus the older ones; however, this is not always the case.
* Evidently, even without a branch predictor, the C++20 <code><nowiki>[[likely]]</nowiki></code> and <code><nowiki>[[unlikely]]</nowiki></code> attributes as well as the GCC intrinsic <code>__builtin_expect()</code> can have a fairly profound impact on code generation and optimization for conditionals and branches. More information can be found [https://dcemulation.org/phpBB/viewtopic.php?t=106029 here].
* <code>-fipa-pta</code> allows the compiler to analyze pointer and reference usage beyond the scope of the current compiling function, which very often results in pretty decent performance increases at the cost of increased compile times and RAM usage.
* <code>-flto</code> allows GCC to perform optimizations over the entire program and all translation units as a single entity during the linking phase, for the cost of increased compile times and RAM usage. This frequently results in more performant code.
* An in-depth benchmark comparing the run-time performance and compiled binary size output of every toolchain version officially supported by KOS with various optimization levels can be found [https://dcemulation.org/phpBB/viewtopic.php?t=106068 here].