Hello! You may call me Ilvir. I got an issue while building U-Boot for MIPS platform, because of __builtin_mips_cache needs optimization flags (like -O2) while non-literal int passed in it ("int op" at example below).
Example code: static inline void mips_cache(int op, const volatile void *addr) { #if __GCC_HAVE_BUILTIN_MIPS_CACHE __builtin_mips_cache(op, addr); #endif } void f() { const void *addr = (const void*)0xB800200; mips_cache(op, addr); } Running compilation without optimization flag: ilvir:~/test/mips_cache$ mips-linux-gnu-gcc -S -march=mips32r2 mips_cache.c mips_cache.c: In function ‘mips_cache’: mips_cache.c:3:9: error: invalid argument to built-in function 3 | __builtin_mips_cache(op, addr); | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ And with: ilvir:~/test/mips_cache$ mips-linux-gnu-gcc -O2 -S -march=mips32r2 mips_cache.c compiles well. Well passed compilation output: ilvir:~/test/mips_cache$ cat mips_cache.s .file 1 "mips_cache.c" .section .mdebug.abi32 .previous .nan legacy .module fp=xx .module nooddspreg .module arch=mips32r2 .abicalls .text .align 2 .globl f .set nomips16 .set nomicromips .ent f .type f, @function f: .frame $sp,0,$31 # vars= 0, regs= 0/0, args= 0, gp= 0 .mask 0x00000000,0 .fmask 0x00000000,0 .set noreorder .set nomacro li $2,192937984 # 0xb800000 jr $31 cache 0x4,512($2) .set macro .set reorder .end f .size f, .-f .ident "GCC: (Debian 12.2.0-14) 12.2.0" .section .note.GNU-stack,"",@progbits Preprocessor output: ilvir:~/test/mips_cache$ mips-linux-gnu-gcc -E -march=mips32r2 mips_cache.c # 0 "mips_cache.c" # 0 "<built-in>" # 0 "<command-line>" # 1 "/usr/mips-linux-gnu/include/stdc-predef.h" 1 3 # 0 "<command-line>" 2 # 1 "mips_cache.c" static inline void mips_cache(int op, const volatile void *addr) { __builtin_mips_cache(op, addr); } void f() { unsigned int op = 0x04; const void *addr = (const void*)0xB800200; mips_cache(op, addr); } Compiler: ilvir:~/test/mips_cache$ mips-linux-gnu-gcc -v Using built-in specs. COLLECT_GCC=mips-linux-gnu-gcc COLLECT_LTO_WRAPPER=/usr/lib/gcc-cross/mips-linux-gnu/12/lto-wrapper Target: mips-linux-gnu Configured with: ../src/configure -v --with-pkgversion='Debian 12.2.0-14' --with-bugurl=file:///usr/share/doc/gcc-12/README.Bugs --enable-languages=c,ada,c++,go,d,fortran,objc,obj-c++,m2 --prefix=/usr --with-gcc-major-version-only --program-suffix=-12 --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new --enable-gnu-unique-object --disable-libitm --disable-libsanitizer --disable-libquadmath --disable-libquadmath-support --enable-plugin --enable-default-pie --with-system-zlib --enable-libphobos-checking=release --without-target-system-zlib --enable-multiarch --disable-werror --enable-multilib --with-arch-32=mips32r2 --with-fp-32=xx --with-lxc1-sxc1=no --enable-targets=all --with-arch-64=mips64r2 --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=mips-linux-gnu --program-prefix=mips-linux-gnu- --includedir=/usr/mips-linux-gnu/include Thread model: posix Supported LTO compression algorithms: zlib zstd gcc version 12.2.0 (Debian 12.2.0-14) It will be very helpful if you tell me the importance of using optimization flags when compiling the built-in given above. Is it really necessary to use optimization flags there? Does the compiler operate right? Thank you!