Implement N32 floating-point regs #78
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AngheloAlf
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Feb 25, 2025
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| if (!n32) { | ||
| // In O32, only even registers can be used as double registers | ||
| assert(reg % 2 == 0); | ||
| } |
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This isn't true, you can use odd registers on o32. That's how doubles are implemented on mips1
Example code from Rocket robot on wheels:
/* B18C 8000A58C 3C018000 */ lui $at, %hi(D_80000630)
/* B190 8000A590 C4210630 */ lwc1 $f1, %lo(D_80000630)($at)
/* B194 8000A594 C4200634 */ lwc1 $f0, %lo(D_80000630 + 0x4)($at)
/* B198 8000A598 4620A083 */ div.d $f2, $f20, $f0
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that code uses $f2, $f20 and $f0 as double registers which are all even. The lwc1 would be handled by wr() above
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Oh, I missed that part. Nice catch
AngheloAlf
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Feb 26, 2025
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| if (!n32) { | ||
| // In O32, only even registers can be used as double registers | ||
| assert(reg % 2 == 0); | ||
| } |
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Oh, I missed that part. Nice catch
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N32 has a full set of 32 FPRs ("FR=1") instead of having odd regs be aliases for the upper halves of even ones. I checked that this PR generates the same code for O32, but the N32 bits are not well-tested because compilers don't do a lot of FP math
And recomp.cpp now has a
--n32flag (similar to--conservative) to analyze N32 code instead of O32