Hello, I found that a built-in function "__builtin_riscv_zicbop_cbo_prefetchi" is terribly broken so that this is practically unusable. It emits the "prefetch.i" machine instruction HINT but with no usable arguments.
Contents of a.c: > void function_to_be_called(void); > > void sample(void) > { > __builtin_riscv_zicbop_cbo_prefetchi(&function_to_be_called); > function_to_be_called(); > } Compiling with the 'Zicbop' extension fails. > $ riscv64-unknown-elf-gcc -O2 -march=rv64i_zicbop -mabi=lp64 -c a.c > a.c: In function 'sample': > a.c:5:42: warning: passing argument 1 of > '__builtin_riscv_zicbop_cbo_prefetchi' makes integer from pointer without a > cast [-Wint-conversion] > 5 | __builtin_riscv_zicbop_cbo_prefetchi(&function_to_be_called); > | ^~~~~~~~~~~~~~~~~~~~~~ > | | > | void (*)(void) > a.c:5:42: note: expected 'long int' but argument is of type 'void (*)(void)' > a.c:5:5: error: invalid argument to built-in function > 5 | __builtin_riscv_zicbop_cbo_prefetchi(&function_to_be_called); > | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ seems the prototype of this built-in function is... > int __builtin_riscv_zicbop_cbo_prefetchi(int); // RV32 > long __builtin_riscv_zicbop_cbo_prefetchi(long); // RV64 I started to have a bad feeling about this. Looking at the test case, following code compiles (sort of). > void sample(void) > { > __builtin_riscv_zicbop_cbo_prefetchi(1); /* integer constant: 0-4 > (inclusive) */ > } WHAT IS THIS PREFETCHING!? The answer was obvious (tested with GCC 13.2.0). > $ riscv64-unknown-elf-gcc -O2 -march=rv64i_zicbop -mabi=lp64 -S a.c > $ cat a.s > .file "a.c" > .option nopic > .attribute arch, "rv64i2p1_zicbop1p0" > .attribute unaligned_access, 0 > .attribute stack_align, 16 > .text > .align 2 > .globl sample > .type sample, @function > sample: > li a5,0 > prefetch.i 0(a5) > ret > .size sample, .-sample > .ident "GCC: (gc891d8dc23e1) 13.2.0" ... none (NULL). Even the prefetching constant (1) is ignored. It makes no sense whatsoever. This patch set is definitely compatibility- breaking but necessary to make "prefetch.i" work. This patch set makes following built-in function. > void __builtin_riscv_zicbop_prefetch_i(void*); Did you notice that I renamed the function? There are three reasons: 1. We needed to break the compatibility anyway. 2. To avoid functionality problems. Co-existing functional and non-functional __builtin_riscv_zicbop_cbo_prefetchi built-in felt like a nightmare. 3. Although this is also a cache block operation, the instruction "prefetch.i" does not have the name "cbo" in it (unlike "__builtin_riscv_zicbom_cbo_clean" corresponding "cbo.clean"). Let's make a working sample (a.c): > void function_to_be_called(void); > > void sample(void) > { > __builtin_riscv_zicbop_prefetch_i(&function_to_be_called); > function_to_be_called(); > } And take look at the output assembly and its relocations. > $ riscv64-unknown-elf-gcc -O2 -march=rv64i_zicbop -mabi=lp64 -S a.c > $ cat a.s > .file "a.c" > .option nopic > .attribute arch, "rv64i2p1_zicbop1p0" > .attribute unaligned_access, 0 > .attribute stack_align, 16 > .text > .align 2 > .globl sample > .type sample, @function > sample: > lui a5,%hi(function_to_be_called) > addi a5,a5,%lo(function_to_be_called) > prefetch.i 0(a5) > tail function_to_be_called > .size sample, .-sample > .ident "GCC: (GNU) 14.0.0 20230810 (experimental)" I hope this issue is fixed soon. Sincerely, Tsukasa Tsukasa OI (1): RISC-V: Make "prefetch.i" built-in usable gcc/config/riscv/riscv-cmo.def | 4 ++-- gcc/config/riscv/riscv.md | 5 ++--- gcc/doc/extend.texi | 7 +++++++ gcc/testsuite/gcc.target/riscv/cmo-zicbop-1.c | 8 +++++--- gcc/testsuite/gcc.target/riscv/cmo-zicbop-2.c | 10 ++++++---- 5 files changed, 22 insertions(+), 12 deletions(-) base-commit: 9b099a83b45b8fcdfc07d518e05d36ea741b2227 -- 2.41.0