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Address Erik's feedback
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@lwaern-intel
lwaern-intel committed Nov 7, 2023
1 parent d9e78d1 commit 08bda7f
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Showing 3 changed files with 32 additions and 28 deletions.
4 changes: 2 additions & 2 deletions py/dml/codegen.py
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Original file line number Diff line number Diff line change
Expand Up @@ -3055,7 +3055,7 @@ def stmt_select(stmt, location, scope):
if_chain = last_stmt
else:
if_chain = codegen_statement(else_ast, location, scope)
if iterations > 50 and isinstance(lst, List):
if iterations > WBIGUNROLL.limit and isinstance(lst, List):
report(WBIGUNROLL(stmt.site,
'#'*(stmt.site.dml_version() != (1, 2))
+ 'select',
Expand Down Expand Up @@ -3186,7 +3186,7 @@ def foreach_constant_list(site, itername, lst, statement, location, scope):
stmt)
spec.append(mkCompound(site, decls + [stmt]))

if len(spec) > 50 and isinstance(lst, List):
if len(spec) > WBIGUNROLL.limit and isinstance(lst, List):
report(WBIGUNROLL(site,
'#'*(site.dml_version() != (1, 2)) + 'foreach',
len(spec)))
Expand Down
9 changes: 5 additions & 4 deletions py/dml/messages.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2012,16 +2012,17 @@ class WHOOKSEND(DMLWarning):
+ "information about the differences between 'send' and 'send_now'")

class WBIGUNROLL(DMLWarning):
"""
limit = 64
__doc__ = f"""
A `#select` or `#foreach` statement was specified which caused DMLC to
study the body and generate duplicated C code for it a large number of
times (more than 50 times.) This can dramatically increase both DMLC and
GCC compile times and code size, if not crash DMLC outright.
times (more than {limit} times.) This can dramatically increase both DMLC
and GCC compile times and code size, if not crash DMLC outright.
To address this, you have two options:
* Ensure most iterations can be entirely eliminated at compile-time by
DMLC. For `#select`, this can be done by ensuring that the `where` check
will be a constant (typically a constant equality) for most if not all
will be a constant value (e.g. a constant equality) for most if not all
items of the specified list. For `#foreach`, encase the body in an `#if`
check that is false for most items of the specified list.
* Don't use `#select` or `#foreach`. Represent the specified compile-time
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47 changes: 25 additions & 22 deletions test/1.2/errors/T_WBIGUNROLL.dml
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Original file line number Diff line number Diff line change
Expand Up @@ -11,61 +11,64 @@ device test;

data int zero = 0;

parameter zeroes_50 = [$zero, $zero, $zero, $zero, $zero, $zero, $zero, $zero,
parameter zeroes_64 = [$zero, $zero, $zero, $zero, $zero, $zero, $zero, $zero,
$zero, $zero, $zero, $zero, $zero, $zero, $zero, $zero,
$zero, $zero, $zero, $zero, $zero, $zero, $zero, $zero,
$zero, $zero, $zero, $zero, $zero, $zero, $zero, $zero,
$zero, $zero, $zero, $zero, $zero, $zero, $zero, $zero,
$zero, $zero, $zero, $zero, $zero, $zero, $zero, $zero,
$zero, $zero];
$zero, $zero, $zero, $zero, $zero, $zero, $zero, $zero,
$zero, $zero, $zero, $zero, $zero, $zero, $zero, $zero];

// Fiftieth zero is constant
parameter zeroes_51 = [$zero, $zero, $zero, $zero, $zero, $zero, $zero, $zero,
// Sixtyfourth zero is constant
parameter zeroes_65 = [$zero, $zero, $zero, $zero, $zero, $zero, $zero, $zero,
$zero, $zero, $zero, $zero, $zero, $zero, $zero, $zero,
$zero, $zero, $zero, $zero, $zero, $zero, $zero, $zero,
$zero, $zero, $zero, $zero, $zero, $zero, $zero, $zero,
$zero, $zero, $zero, $zero, $zero, $zero, $zero, $zero,
$zero, $zero, $zero, $zero, $zero, $zero, $zero, $zero,
$zero, $zero, $zero, $zero, $zero, $zero, $zero, $zero,
$zero, 0, $zero];
$zero, $zero, $zero, $zero, $zero, $zero, $zero, 0,
$zero];

bank b {
register regs[i in 0..50] size 4 @ undefined;
register regs[i in 0..64] size 4 @ undefined;
}

method init {
local int i;
local int nonconstant;

// no warning
foreach x in ($zeroes_50) assert true;
foreach x in ($zeroes_64) assert true;
// The else branch is not considered an iteration
select x in ($zeroes_50) where (x == i) {
select x in ($zeroes_64) where (x == nonconstant) {
assert true;
} else assert true;

/// WARNING WBIGUNROLL
foreach x in ($zeroes_51) assert true;
foreach x in ($zeroes_65) assert true;
/// WARNING WBIGUNROLL
select x in ($zeroes_51) where (x == i) {
select x in ($zeroes_65) where (x == nonconstant) {
assert true;
} else assert true;

// no warning
foreach x in ($zeroes_51) {
// As fiftieth bit is constant 0, DML 1.2 semantics eliminates this if
// entirely, and subsequently causes that iteration to be omitted from
// codegen entirely; reducing the total count to 50
foreach x in ($zeroes_65) {
// As sixtyfourth bit is constant 0, DML 1.2 semantics eliminates this
// if, and subsequently causes that iteration to be omitted from
// codegen entirely; reducing the total count to 64
if (x != 0) assert true;
}

// As fiftieth bit is constant 0, select can cut short at it, reducing the
// total number of iterations to 50
select x in ($zeroes_50) where (x == 0) {
// As sixtyfourth bit is constant 0, select can cut short at it, reducing
// the total number of iterations to 64
select x in ($zeroes_65) where (x == 0) {
assert true;
} else assert true;

// As fiftieth bit is constant 0, select can omit the check and thus
// iteration for it, reducing the total number of iterations to 50
select x in ($zeroes_50) where (x == 1) {
// As sixtyfourth bit is constant 0, select can omit the check and thus
// iteration for it, reducing the total number of iterations to 64
select x in ($zeroes_65) where (x != 0) {
assert true;
} else assert true;

Expand All @@ -74,7 +77,7 @@ method init {
// syntax, not the object lists generated by DMLC
// no warning
foreach x in ($b.unmapped_registers) assert true;
select x in ($b.unmapped_registers) where (i == 0) {
select x in ($b.unmapped_registers) where (x == nonconstant) {
assert true;
} else assert true;
}

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