Re: transpiling to low level C

On 16/12/2024 04:02, BGB wrote:

On 12/15/2024 5:22 PM, Thiago Adams wrote:

Em 12/15/2024 7:22 PM, Lawrence D'Oliveiro escreveu:

On Sun, 15 Dec 2024 07:44:34 -0300, Thiago Adams wrote:
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I also think LLVM is too big.

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How about QBE, then <https://c9x.me/compile/>.

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QBE is just for linux and it does not generate code directly. C is everywhere.
But I am reading QBE docs to see what is necessary in a IL.
>

 I agree that both LLVM and GCC are too big.
 I am not sure the minimum size of a usable C compiler, my current estimate is probably somewhere in the area of 50-100 kLOC.
 

My hope is 10-30K lines. But remember this is a simpler version of C. This is the objective. It also may work in one pass, without building a lot of data structures for the AST.

My current compiler is a bit bigger than this, and my own past attempt to implement a C compiler in under 30k lines had failed.
 My current compiler use to be smaller, but multiple backends and similar did make it bigger:
   SH-2, SH-4, BJX1 (older)
   BJX2, RISC-V (current)
   If I were to estimate a feature set for a 3AC IL:
   Basic UNARY and BINARY operators;
     Also COMPARE and similar;
   Load and Store Index operators;
     With support for an immediate index;
   GOTO
   IF-GOTO
   CALL (with a list of argument variables and a target variable).
 One doesn't need any higher-level control flow constructs.
 Any built-in support for "switch()" can be optional (the main reason to have so is that it can make switch a little faster, but isn't required).
 Earlier on, my compiler didn't have any backend support for this, and would instead decompose the switch into "if/else/goto" logic. You can then use recursive binary subdivision to implement the list of case labels (or linear probes if N is small).
 BGBCC still uses binary subdivide if the case-labels don't satisfy the constraints for a branch-table (Say, needs to be 16..256 case labels with a density over 75%).
 

Yes, switch is something I can remove.
C2Y is adding range in case. (https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3370.htm)