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Refine the top-level documentation
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@jserv
jserv committed Sep 23, 2023
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Expand Up @@ -9,15 +9,14 @@ a self-compiling compiler for a subset of the C language.

### Features

* Generate executable Linux ELF binaries for ARMv7-A and RV32IM;
* Provide a minimal C standard library for basic I/O on GNU/Linux;
* The cross-compiler is written in ANSI C, arguably running on most platforms;
* Self-contained C language front-end and machine code generator;
* Two-pass compilation: on the first pass, it checks the syntax and destructs
complex statements to basic operations, while on the second pass, it actually
translates the basic operations into Arm/RISC-V machine code.
* Register allocation: compatible with different architecture that the number of
available registers could be different (needs at least 7 available registers for now)
* Generate executable Linux ELF binaries for ARMv7-A and RV32IM.
* Provide a minimal C standard library for basic I/O on GNU/Linux.
* The cross-compiler is written in ANSI C, making it compatible with most platforms.
* Offer a self-contained C language front-end and machine code generator.
* Utilize a two-pass compilation process: the first pass checks syntax and breaks down complex statements into basic operations,
while the second pass translates these operations into Arm/RISC-V machine code.
* Implement register allocation compatible with various architectures,
although the number of available registers may differ (currently requires at least 7 available registers).

## Compatibility

Expand Down Expand Up @@ -139,42 +138,43 @@ $ out/shecc --dump-ir -o fib tests/fib.c
```

Line-by-line explanation between C source and IR:
```asm
```c
C Source IR Explanation
-----------------------+-------------------------------------------+-------------------------------------------------------------------------------------------------
int fib(int n) def int @fib(int %n) Indicate a function definition
{ {
if (n == 0) const %.t1001, $0 Load constant 0 into a temporary variable ".t1001"
%.t1002 = eq %n, %.t1001 Test "n" equals ".t1001" or not, and write the result in temporary variable ".t1002"
br %.t1002, .label.1177, .label.1178 If ".t1002" equals zero, goto false label ".label.1178", otherwise, goto true label ".label.1177"
.label.1177
return 0; const %.t1003, $0 Load constant 0 into a temporary variable ".t1003"
ret %.t1003 Return ".t1003"
j .label.1179 Jump to endif label ".label.1179"
.label.1178
else if (n == 1) const %.t1004, $1 Load constant 1 into a temporary variable ".t1004"
%.t1005 = eq %n, %.t1004 Test "n" equals ".t1004" or not, and write the result in temporary variable ".t1005"
br %.t1005, .label.1183, .label.1184 If ".t1005" equals zero, goto false label ".label.1184". Otherwise, goto true label ".label.1183"
.label.1183
return 1; const %.t1006, $1 Load constant 1 into a temporary variable ".t1006"
ret %.t1006 Return ".t1006"
.label.1184
.label.1179
return
fib(n - 1) const %.t1007, $1 Load constant 1 into a temporary variable ".t1007"
%.t1008 = sub %n, %.t1007 Subtract ".t1007" from "n", and store the result in temporary variable ".t1008"
push %.t1008 Prepare parameter for function call
call @fib, 1 Call function "fib" with one parameter
+ retval %.t1009 Store return value in temporary variable ".t1009"
fib(n - 2); const %.t1010, $2 Load constant 2 into a temporary variable ".t1010"
%.t1011 = sub %n, %.t1010 Subtract ".t1010" from "n", and store the result in temporary variable ".t1011"
push %.t1011 Prepare parameter for function call
call @fib, 1 Call function "fib" with one parameter
retval %.t1012 Store return value in temporary variable ".t1012"
%.t1013 = add %.t1009, %.t1012 Add ".t1009" and ".t1012", and store the result in temporary variable ".t1013"
ret %.t1013 Return ".t1013"
} }
------------------+---------------------------------------+----------------------------------------------------------------------------------

int fib(int n) def int @fib(int %n) Indicate a function definition
{ {
if (n == 0) const %.t1001, $0 Load constant 0 into a temporary variable ".t1001"
%.t1002 = eq %n, %.t1001 Test "n" equals ".t1001" or not, and write the result in temporary variable ".t1002"
br %.t1002, .label.1177, .label.1178 If ".t1002" equals zero, goto false label ".label.1178", otherwise,
goto true label ".label.1177"
.label.1177
return 0; const %.t1003, $0 Load constant 0 into a temporary variable ".t1003"
ret %.t1003 Return ".t1003"
j .label.1184 Jump to endif label ".label.1184"
.label.1178
else if (n == 1) const %.t1004, $1 Load constant 1 into a temporary variable ".t1004"
%.t1005 = eq %n, %.t1004 Test "n" equals ".t1004" or not, and write the result in temporary variable ".t1005"
br %.t1005, .label.1183, .label.1184 If ".t1005" equals zero, goto false label ".label.1184". Otherwise,
goto true label ".label.1183"
.label.1183
return 1; const %.t1006, $1 Load constant 1 into a temporary variable ".t1006"
ret %.t1006 Return ".t1006"
.label.1184
return
fib(n - 1) const %.t1007, $1 Load constant 1 into a temporary variable ".t1007"
%.t1008 = sub %n, %.t1007 Subtract ".t1007" from "n", and store the result in temporary variable ".t1008"
push %.t1008 Prepare parameter for function call
call @fib, 1 Call function "fib" with one parameter
+ retval %.t1009 Store return value in temporary variable ".t1009"
fib(n - 2); const %.t1010, $2 Load constant 2 into a temporary variable ".t1010"
%.t1011 = sub %n, %.t1010 Subtract ".t1010" from "n", and store the result in temporary variable ".t1011"
push %.t1011 Prepare parameter for function call
call @fib, 1 Call function "fib" with one parameter
retval %.t1012 Store return value in temporary variable ".t1012"
%.t1013 = add %.t1009, %.t1012 Add ".t1009" and ".t1012", and store the result in temporary variable ".t1013"
ret %.t1013 Return ".t1013"
} }
```
## Known Issues
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