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RFC: Simplify bounds checks for multi-dimensional array accesses #18064

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Aug 23, 2016
Merged

RFC: Simplify bounds checks for multi-dimensional array accesses #18064

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32 changes: 26 additions & 6 deletions src/cgutils.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1247,6 +1247,14 @@ static void assign_arrayvar(jl_arrayvar_t &av, const jl_cgval_t &ainfo, jl_codec
builder.CreateStore(emit_arraysize(ainfo, i+1, ctx), av.sizes[i]);
}

// Returns the size of the array represented by `tinfo` for the given dimension `dim` if
// `dim` is a valid dimension, otherwise returns constant one.
static Value *emit_arraysize_for_unsafe_dim(const jl_cgval_t &tinfo, jl_value_t *ex, size_t dim,
size_t nd, jl_codectx_t *ctx)
{
return dim > nd ? ConstantInt::get(T_size, 1) : emit_arraysize(tinfo, ex, dim, ctx);
}

static Value *emit_array_nd_index(const jl_cgval_t &ainfo, jl_value_t *ex, size_t nd, jl_value_t **args,
size_t nidxs, jl_codectx_t *ctx)
{
Expand All @@ -1267,12 +1275,12 @@ static Value *emit_array_nd_index(const jl_cgval_t &ainfo, jl_value_t *ex, size_
for(size_t k=0; k < nidxs; k++) {
idxs[k] = emit_unbox(T_size, emit_expr(args[k], ctx), NULL);
}
Value *ii;
for(size_t k=0; k < nidxs; k++) {
Value *ii = builder.CreateSub(idxs[k], ConstantInt::get(T_size, 1));
ii = builder.CreateSub(idxs[k], ConstantInt::get(T_size, 1));
i = builder.CreateAdd(i, builder.CreateMul(ii, stride));
if (k < nidxs-1) {
Value *d =
k >= nd ? ConstantInt::get(T_size, 1) : emit_arraysize(ainfo, ex, k+1, ctx);
Value *d = emit_arraysize_for_unsafe_dim(ainfo, ex, k+1, nd, ctx);
#if CHECK_BOUNDS==1
if (bc) {
BasicBlock *okBB = BasicBlock::Create(jl_LLVMContext, "ib");
Expand All @@ -1287,9 +1295,21 @@ static Value *emit_array_nd_index(const jl_cgval_t &ainfo, jl_value_t *ex, size_
}
#if CHECK_BOUNDS==1
if (bc) {
Value *alen = emit_arraylen(ainfo, ex, ctx);
// if !(i < alen) goto error
builder.CreateCondBr(builder.CreateICmpULT(i, alen), endBB, failBB);
// We have already emitted a bounds check for each index except for
// the last one which we therefore have to do here.
bool linear_indexing = nidxs < nd;
if (linear_indexing) {
// Compare the linearized index `i` against the linearized size of
// the accessed array, i.e. `if !(i < alen) goto error`.
Value *alen = emit_arraylen(ainfo, ex, ctx);
builder.CreateCondBr(builder.CreateICmpULT(i, alen), endBB, failBB);
} else {
// Compare the last index of the access against the last dimension of
// the accessed array, i.e. `if !(last_index < last_dimension) goto error`.
Value *last_index = ii;
Value *last_dimension = emit_arraysize_for_unsafe_dim(ainfo, ex, nidxs, nd, ctx);
builder.CreateCondBr(builder.CreateICmpULT(last_index, last_dimension), endBB, failBB);
}

ctx->f->getBasicBlockList().push_back(failBB);
builder.SetInsertPoint(failBB);
Expand Down