atrosinenko added inline comments.
================ Comment at: compiler-rt/lib/builtins/fp_lib.h:49 -static __inline int rep_clz(rep_t a) { return __builtin_clz(a); } +static __inline int rep_clz(rep_t a) { return clzsi(a); } ---------------- MaskRay wrote: > Why is this needed? First of all, I will compile the examples with gcc because right now I most probably don't have a TI sysroot for MSP430 compatible with the mainline clang and testing with my locally patched llvm+clang seems even less correct than with gcc. The problem is that the definition, according to the [gcc documentation](https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html) is `int __builtin_clz (unsigned int x)`. This builtin is defined with the "default size" `int` argument, not `uint32_t` or `int32_t`. Yes, there are `int`s in the specifications that are not exactly `int` but something "expected to be int" actually expressed via machine modes. But here it looks like it is actually an int: ```lang=cpp,name=clzsi_test.c #include <stdio.h> #include <stdint.h> typedef uint32_t rep_t; static int rep_clz(rep_t a) { return __builtin_clz(a); } int main() { printf("sizeof(int) = %d\n", (int)sizeof(int)); printf("first: %d\n", rep_clz(0x1000)); printf("second: %d\n", rep_clz(0x10000)); printf("third: %d\n", rep_clz(0x100000)); } ``` When compiled and launched on x86_64 Linux host, it prints the expected results: ``` $ gcc -Wall clzsi_test.c -o clzsi_test && ./clzsi_test sizeof(int) = 4 first: 19 second: 15 third: 11 ``` Let's compile and run it with ``` $ $sysroot/bin/msp430-elf-gcc --version msp430-elf-gcc (Mitto Systems Limited - msp430-gcc 8.3.1.25) 8.3.1 Copyright (C) 2018 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. ``` Then we get the following (the `-msim` option is necessary to run the compiled binary with `msp430-elf-run` simulator): ``` $ $sysroot/bin/msp430-elf-gcc -msim -Wall clzsi_test.c -o clzsi_test && $sysroot/bin/msp430-elf-run ./clzsi_test sizeof(int) = 2 first: 3 second: 16 third: 16 ``` So, these are expected results for `clz(i16 arg)` (with the third line being an UB at all) but not the results expected for `rep_t`-sized argument. //(When I comment out the third `printf`, other output that now is expected to be UB-free remains unchanged)// When I change `rep_clz` to use `__builtin_clzl`, the output on MSP430 simulator differs from the host one just in the `sizeof...` line, as expected. ``` sizeof(int) = 2 first: 19 second: 15 third: 11 ``` Of course, now it will output not the expected values on x86_64, so using `clzsi` instead of a hardcoded name. Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D81408/new/ https://reviews.llvm.org/D81408 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits