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Writing a Compiler Using LLVM: Building a BigNum Calculator

This tutorial walks through how to implement a compiler using LLVM for a scientific calculator. An introduction to LLVM and it's tool chain is available here.

Build and Run

Compile and run LLVM from the source and add the bin folder into $PATH.

Using System Default

Reference: https://andreasfertig.blog/2021/02/clang-and-gcc-on-macos-catalina-finding-the-include-paths/

$ export SDKROOT="`xcrun --show-sdk-path`"
$ clang++ -std=c++20  src/*.cpp `llvm-config --cxxflags --ldflags --system-libs --libs core` -g -o bignum1 
$ ./bignum1 "2 + 7" | llc -filetype=obj -o=bignum1.o 
$ clang -o bignum bignum1.o src/rtcalc.c
$ ./bignum
result: 9

Passing Header and Library Paths Externally

This produced missing headers although header and library locations are passed externally. Just record here for reference.

$ clang++ \
		-I/Users/kumarasiri/work/intbricks/llvm-project-llvmorg-14.0.0/install/include/c++/v1 \
		-I/Library/Developer/CommandLineTools/SDKs/MacOSX13.1.sdk/usr/include/ \
		-I/Users/kumarasiri/work/intbricks/llvm-project-llvmorg-14.0.0/install/include \
		-L/Library/Developer/CommandLineTools/SDKs/MacOSX13.1.sdk/usr/lib \
		-L/Users/kumarasiri/work/intbricks/llvm-project-llvmorg-14.0.0/install/lib \
		 -std=c++20  src/*.cpp `llvm-config --cxxflags --ldflags --system-libs --libs core` -g -o bignum1
$ ./bignum1 "2 + 7" | llc -filetype=obj -o=bignum1.o
$ clang -o bignum bignum1.o src/rtcalc.c
$ ./bignum 
result: 9

./bignum1 "2 + 3" | llc -filetype=obj -o=bignum1.o
$LLVM_DIR/bin/clang -cc1 src/rtcalc.c -o bignum1.o bignum
./bignum

Unary Operators

Name Operator Description
Index generator iota B Vector of the first B integers
Random number generator ?B Random number between 0 and B

Binary operators

A, B can be scalars or vectors, or multi-dimensional vectors (matrices).

Name Operator Description
Add A + B Sum A and B
Subtract A - B A subtract B
Multiply A * B A multiplied by B
Shift n << A Shift A by n times

Examples

Expression Result
23 23
23 + 45 68
1e10 10000000000
1e100 1e100
2 ** 64 1.8446744e+19
2 ** 640 4.562441e+192
2.1 + 3.2 5.3
2.121212122121 + 3.1212121212 5.24242424332
1 2 3 4 5 6 [1 2 3 4 5 6] (Vector)
1 2 3 + 4 5 6 [5 7 9]
itoa 10 [1 2 3 4 5 6 7 8 9 10]
2 ** itoa 10 [2 4 8 16 32 64]
(2 ** itoa 100) == (1<<itoa 100)
5 rho 1 [1 1 1 1 1]
5 5 rho 1 5x5 matrix of values 1
5 5 itoa 1 5x5 matrix of 1..25
?100 Random number between 0 and 100
?10 rho 100 Vector of size (1x100) of random numbers below between 0 and 10
1 << 1 2 3 4 5 [2 4 8 16 32]
2 * log(10) 4.605170185988092
+/itoa 15 120 (add first 15 numbers together)
1 * 2 * 3 6 (3!)
*/itoa 3 6
2*itoa 2 + 3 2 4 6 8 10

Grammar

Statement      -> Expression
               
Expression     -> Operand
                | Operand BinaryOp Expression
               
Operand        -> ( Expression )
               | Operand
               | Number
               | Rational
               | Vector
               | Operand [ Expression ]
               | UnaryOperator Expression

BinaryOperator | +
               | -  
               | /  
               | *
               | **
               | e
               | rho
               | itoa
               | shift

UnaryOperator  | itoa
               | ?
               | <<

Parsing Rules

  • Unary operators apply to the rest of the line
  • Binary operators apply to the operand on left, rest of the line on right
  • Associative to the right

References