Return overwrite #2

New Issue

TheCurle · 2020-09-11T02:19:59Z

TheCurle commented

2020-09-11 02:19:59 +00:00

Consider the following ASM snippet generated by build 10:

movq	$10, %r8
movq	%r8, %rcx
call	OtherFunctionThatReturns40
movq	%rax, %r9 <--
movq	$10, %r9 <--
addq	%r9, %r9 <--
movq	%r9, %rcx 
call	PrintInteger

See the three highlighted lines.
As it currently stands, the register used to output a variable is deallocated as soon as it is populated, allowing the compiler to use the register immediately upon the next assignment.
This leads to things like Print(Function() + 10) behaving like Print(10 + 10).

This could be fixed by just not deallocating the register after it's used, but there would need to be other systems in place to garbage check the register.

Consider the following ASM snippet generated by build 10: movq $10, %r8 movq %r8, %rcx call OtherFunctionThatReturns40 movq %rax, %r9 <-- movq $10, %r9 <-- addq %r9, %r9 <-- movq %r9, %rcx call PrintInteger See the three highlighted lines. As it currently stands, the register used to output a variable is deallocated as soon as it is populated, allowing the compiler to use the register immediately upon the next assignment. This leads to things like `Print(Function() + 10)` behaving like `Print(10 + 10)`. This could be fixed by just not deallocating the register after it's used, but there would need to be other systems in place to garbage check the register.

TheCurle added the

bug

invalid

labels 2020-09-11 02:26:21 +00:00

TheCurle referenced this issue from a commit

2020-09-11 02:31:53 +00:00

Fix stupid bug. Closes #2

TheCurle closed this issue

2020-09-11 02:31:53 +00:00

TheCurle commented

2020-09-11 02:33:14 +00:00

I'm actually embarrassed about this one. After spending a day or two working on other things, i realised that i was actually trying to deallocate the register used to input the value. Instead i was deallocating the one used to output, hence... stupid bug.

Onto bigger fish!

I'm actually embarrassed about this one. After spending a day or two working on other things, i realised that i was actually trying to deallocate the register used to *input* the value. Instead i was deallocating the one used to *output*, hence... stupid bug. Onto bigger fish!

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