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Example - 2-D Random Walk

This is an example of compiling a very naieve implementation of a 2-D random walk. 

library(Rllvm)
InitializeNativeTarget()
mod = Module("2Drw")
ptrInt = pointerType(Int32Type)
fun = Function("rw2d", VoidType, c(x = ptrInt, y = ptrInt, len = Int32Type), mod)

entry = Block(fun, "entry")
cond = Block(fun, "loopCond")
body = Block(fun, "loopBody")
ret = Block(fun, "return")
h = Block(fun, "Horizontal")
v = Block(fun, "Vertical")
increment = Block(fun, "increment")

one = createIntegerConstant(1L)
minusOne = createIntegerConstant(-1L)

ir = IRBuilder(entry)

iv = ir$createLocalVariable(Int32Type, "i")
lena = ir$createLocalVariable(Int32Type, "lenp")
xa = ir$createLocalVariable(ptrInt, "xp")
ya = ir$createLocalVariable(ptrInt, "yp")
delta = ir$createLocalVariable(Int32Type, "delta")
ir$createStore(fun$x, xa)
ir$createStore(fun$y, ya)
ir$createStore(fun$len, lena)
ir$createStore(one, iv)
ir$createBr(cond)

ir$setInsertPoint(cond)
a = ir$createLoad(iv)
b = ir$createLoad(lena)
ok = ir$createICmp(ICMP_SLT, a, b)
ir$createCondBr(ok, body, ret)

ir$setInsertPoint(ret)
ir$createRetVoid()

ir$setInsertPoint(body)
 # declare runif which takes a number but ignores it. 
runif = Function("runif", DoubleType, c(n = Int32Type), mod)

 # compute delta
u = ir$createCall(runif, one)
gt = ir$createFCmp(FCMP_UGE, u, createDoubleConstant(.5))
ir$createStore(ir$createSelect(gt, minusOne, one),  delta)

 # now determine whether to go horiz or vert.
u = ir$createCall(runif, one)
gt = ir$createFCmp(FCMP_UGE, u, createDoubleConstant(.5))

ir$createCondBr(gt, h, v)

ir$setInsertPoint(h)
a = ir$createLoad(iv)
b = ir$binOp(Sub, a, one)
r = ir$createLoad(xa)
idx = ir$createSExt(b, 64L)
x.prev = ir$createLoad(ir$createGEP(r, idx))
nw = ir$binOp(Add, x.prev, ir$createLoad(delta))
a = ir$createLoad(xa)
i = ir$createLoad(iv)
idx = ir$createSExt(i, 64L)
xi = ir$createGEP(a, idx)
ir$createStore(nw, xi)

a = ir$createLoad(iv)
b = ir$binOp(Sub, a, one)
r = ir$createLoad(ya)
idx = ir$createSExt(b, 64L)
y.prev = ir$createLoad(ir$createGEP(r, idx))
a = ir$createLoad(ya)
i = ir$createLoad(iv)
idx = ir$createSExt(i, 64L)
yi = ir$createGEP(a, idx)
ir$createStore(y.prev, yi)

ir$createBr(increment)

ir$setInsertPoint(increment)
i = ir$createLoad(iv)
inc = ir$binOp(Add, i, 1L)
ir$createStore(inc, iv)
ir$createBr(cond)

ir$setInsertPoint(v)

a = ir$createLoad(iv)
b = ir$binOp(Sub, a, one)
r = ir$createLoad(ya)
idx = ir$createSExt(b, 64L)
y.prev = ir$createLoad(ir$createGEP(r, idx))
nw = ir$binOp(Add, y.prev, ir$createLoad(delta))
a = ir$createLoad(ya)
i = ir$createLoad(iv)
idx = ir$createSExt(i, 64L)
yi = ir$createGEP(a, idx)
ir$createStore(nw, yi)


a = ir$createLoad(iv)
b = ir$binOp(Sub, a, one)
r = ir$createLoad(xa)
idx = ir$createSExt(b, 64L)
x.prev = ir$createLoad(ir$createGEP(r, idx))
a = ir$createLoad(xa)
i = ir$createLoad(iv)
idx = ir$createSExt(i, 64L)
xi = ir$createGEP(a, idx)
ir$createStore(x.prev, xi)



ir$createBr(increment)
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