Link time optimization breaks build: no match insn: amcas_db_d $r12,$r25,$r15

[asheplyakov]

When link time optimization is enabled the code fails to build with a lot of assembler errors like:

{standard input}:607403: Error: no match insn: amcas_d  $r12,$r15,$r16  
{standard input}:611922: Error: no match insn: amcas_db_d       $r12,$r13,$r23
{standard input}:612148: Error: no match insn: amcas_db_d       $r13,$r25,$r14
{standard input}:612188: Error: no match insn: amcas_db_d       $r12,$r25,$r15
{standard input}:614413: Error: no match insn: amcas_d  $r12,$r15,$r18  
{standard input}:621115: Error: no match insn: amcas_d  $r12,$r15,$r18  
{standard input}:622330: Error: no match insn: amcas_db_d       $r12,$r4,$r13
{standard input}:622673: Error: no match insn: amcas_db_d       $r12,$r4,$r13
{standard input}:623031: Error: no match insn: amcas_d  $r12,$r15,$r16  
{standard input}:627166: Error: no match insn: amcas_d  $r12,$r15,$r18  
{standard input}:632288: Error: no match insn: amcas_db_d       $r12,$r13,$r15

The problem is that the compiler is free to reorder (or even eliminate) top-level asm statements,
hence amcas_d macro (defined in src/hotspot/os_cpu/linux_loongarch/amcas_asm.h) might be missing when processing inline assembly in src/hotspot/os_cpu/linux_loongarch/atomic_linux_loongarch.hpp.

To avoid the problem one can include macros definition from inline assembly, i.e. with .include \"amcas_asm.h\", and set proper assembler flags so the assembler can locate amcas_asm.h file (like -Wa,-I -Wa,src/hotspot/os_cpu/linux_loongarch or similar)

[theaoqi]

Hi @asheplyakov, thanks for reporting this issue. We will follow up. It’s the Chinese New Year holiday right now, so it might take some time.

[sunny868]

@asheplyakov How can I reproduce this problem? What is the compilation environment you are using?

[asheplyakov]

@asheplyakov How can I reproduce this problem?

Just enable link time optimization:

bash configure --with-extra-cflags='-O2 -flto=auto' --with-extra-cxxflags='-O2 -flto=auto' --with-extra-ldflags='-O2 -flto=auto'
make images

What is the compilation environment you are using?

• GCC 13.2 with LoongArch SIMD patches
• Binutils 2.41
  (From current ALT Linux sisyphus_loongarch64)