https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93532
--- Comment #12 from Jim Wilson <wilson at gcc dot gnu.org> --- A bisection on mainline between the gcc-8 and gcc-9 releases shows that this testcase was fixed by a combine patch for PR87600 that stops combining hard regs with pseudos to reduce register pressure. The commentary refers to ira and lra problems. A combine patch won't be as safe as a RISC-V backend patch though. I tried testing the riscv HARD_REGNO_CALLER_SAVE_MODE patch with buildroot but it turns out that it is downloading a pre-built compiler instead of building one. So dropping in the patch doesn't do anything. I will have to figure out what is going on there. Trying the riscv patch with mainline on the testcase, I see that I get better rematerialization without the confusing subregs, and I also get smaller stack frames since we are saving SFmode now to the stack instead of DFmode now. Otherwise, I don't see any significant changes to the code. I tried a make check with the riscv patch on mainline, and got an unexpected g++ testsuite failure, so I will have to look into that.
