multiplication, i32, i64, __muldi3, __mulsi3

[alexanderFell]

Hey all,
I am hoping, someone can point me out what I am doing wrong. I would like to compile the following program:

#include <stdlib.h>
int main(int argc, char** argv) {
short a = atoi(argv[1]);
short b = atoi(argv[2]);
return a * b;
}

I am trying to compile it and it results in
riscv64-unknown-linux-gnu-clang++ --sysroot=../../sysroot/ multiplier.cpp -S -o multiplier.S
riscv64-unknown-linux-gnu-g++ multiplier.S -o multiplier.riscv --static
/tmp/ccLOnAlk.o: In function 'main':
multiplier.cpp:(.text+0x68): undefined reference to '__mulsi3'
collect2: error: ld returned 1 exit status
Makefile:26: recipe for target 'multiplier.riscv' failed
make: *** [multiplier.riscv] Error 1

multiplier.S:
.text
.file "multiplier1.cpp"
.globl main
.p2align 2
.type main,@function
main:
addi x2, x2, -64
sd x1, 56(x2)
sd x8, 48(x2)
add x8, x2, x0
addiw x5, x10, 0
addi x10, x11, 0
sw x0, 44(x8)
sw x5, 40(x8)
sd x11, 32(x8)
ld x11, 8(x11)
lui x6, %hi(atoi)
addi x6, x6, %lo(atoi)
sd x10, 16(x8)
addi x10, x11, 0
sd x6, 8(x8)
jalr x1, x6, 0
sh x10, 30(x8)
ld x6, 32(x8)
ld x10, 16(x6)
ld x6, 8(x8)
jalr x1, x6, 0
sh x10, 28(x8)
lh x5, 30(x8)
lh x7, 28(x8)
addiw x10, x5, 0
addiw x11, x7, 0
jal x1, __mulsi3
add x2, x8, x0
ld x8, 48(x2)
ld x1, 56(x2)
addi x2, x2, 64
ret
Lfunc_end0:
.size main, Lfunc_end0-main

The issue here is the __mulsi3 call, which seems to be missing in the following riscv toolchain. If I change the type of a and b to long (anything with a word size that is larger than int) __mulsi3 is replaced by __muldi3, which is defined by the RISCV toolchain and consists of a software multiplication.

I am pretty sure I made a mistake and I forgot a flag somewhere telling clang to use a hardware multiplier (mul, mulw,...), but I have no idea, what the flag should look like (I am new to llvm and riscv). I saw in RISCVInstrInfoM.td that it requires "HasM" but I do not know, where to put it.

Thanks a lot in advance,
Alex

[alexanderFell]

Okay I tried the whole day, 5 minutes after submitting this issue, I figured it out:
It seems, clang didn't know, that I have a multiplier (as suspected), so changing the clang++ invocation like to:

riscv64-unknown-linux-gnu-clang++ --sysroot=../../sysroot/ multiplier.cpp -S -mriscv=RV64IAM -o multiplier.S

did the trick. Sorry for the noise created.

[byllgrim]

Sorry for the noise created.

I'm happy for this noise, as it helped me just now.