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C++ IR: Fix performance of large array value init

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There were two problems here.

1. The inline predicates `isInitialized` and `isValueInitialized` on
   `ArrayAggregateLiteral` caused their callers to materialize every
   `int` that was a valid index into the array. This was slow on huge
   value-initialized arrays.
2. The `isInitialized` predicate was used in the `TInstructionTag` IPA
   type, creating a numbered tuple for each integer in it. This seemed
   to be entirely unnecessary since the `TranslatedElement`s using those
   tags were already indexed appropriately.
This commit is contained in:
Jonas Jensen
2019-07-04 14:27:09 +02:00
parent 0b06cb866b
commit d378da33e8
8 changed files with 121 additions and 35 deletions
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7
cpp/ql/src/semmle/code/cpp/exprs/Literal.qll
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@@ -255,9 +255,10 @@ class ArrayAggregateLiteral extends AggregateLiteral {
* list, either explicitly with an expression, or implicitly value
* initialized.
*/
pragma[inline]
bindingset[elementIndex]
predicate isInitialized(int elementIndex) {
elementIndex in [0..arrayType.getArraySize() - 1]
elementIndex >= 0 and
elementIndex < arrayType.getArraySize()
}
/**
@@ -268,7 +269,7 @@ class ArrayAggregateLiteral extends AggregateLiteral {
* of an object to `false`, `0`, `nullptr`, or by calling the default
* constructor, as appropriate to the type.
*/
pragma[inline]
bindingset[elementIndex]
predicate isValueInitialized(int elementIndex) {
isInitialized(elementIndex) and
not exists(getElementExpr(elementIndex))

35
cpp/ql/src/semmle/code/cpp/ir/implementation/raw/internal/InstructionTag.qll
View File

@@ -9,12 +9,6 @@ private predicate fieldIsInitialized(Field field) {
)
}
private predicate elementIsInitialized(int elementIndex) {
exists(ArrayAggregateLiteral initList |
initList.isInitialized(elementIndex)
)
}
newtype TInstructionTag =
OnlyInstructionTag() or // Single instruction (not including implicit Load)
InitializeThisTag() or
@@ -73,18 +67,10 @@ newtype TInstructionTag =
InitializerFieldDefaultValueStoreTag(Field field) {
fieldIsInitialized(field)
} or
InitializerElementIndexTag(int elementIndex) {
elementIsInitialized(elementIndex)
} or
InitializerElementAddressTag(int elementIndex) {
elementIsInitialized(elementIndex)
} or
InitializerElementDefaultValueTag(int elementIndex) {
elementIsInitialized(elementIndex)
} or
InitializerElementDefaultValueStoreTag(int elementIndex) {
elementIsInitialized(elementIndex)
} or
InitializerElementIndexTag() or
InitializerElementAddressTag() or
InitializerElementDefaultValueTag() or
InitializerElementDefaultValueStoreTag() or
AsmTag() or
AsmInputTag(int elementIndex) {
exists(AsmStmt asm |
@@ -159,15 +145,10 @@ string getInstructionTagId(TInstructionTag tag) {
) and
result = tagName + "(" + index + ")"
) or
exists(int index, string tagName |
(
tag = InitializerElementIndexTag(index) and tagName = "InitElemIndex" or
tag = InitializerElementAddressTag(index) and tagName = "InitElemAddr" or
tag = InitializerElementDefaultValueTag(index) and tagName = "InitElemDefVal" or
tag = InitializerElementDefaultValueStoreTag(index) and tagName = "InitElemDefValStore"
) and
result = tagName + "(" + index + ")"
) or
tag = InitializerElementIndexTag() and result = "InitElemIndex" or
tag = InitializerElementAddressTag() and result = "InitElemAddr" or
tag = InitializerElementDefaultValueTag() and result = "InitElemDefVal" or
tag = InitializerElementDefaultValueStoreTag() and result = "InitElemDefValStore" or
tag = AsmTag() and result = "Asm" or
exists(int index |
tag = AsmInputTag(index) and result = "AsmInputTag(" + index + ")"

2
cpp/ql/src/semmle/code/cpp/ir/implementation/raw/internal/TranslatedElement.qll
View File

@@ -441,7 +441,7 @@ private predicate isFirstValueInitializedElementInRange(
initList.isValueInitialized(elementIndex) and
(
elementIndex = 0 or
not initList.isValueInitialized(elementIndex - 1)
exists(initList.getElementExpr(elementIndex - 1))
)
}

8
cpp/ql/src/semmle/code/cpp/ir/implementation/raw/internal/TranslatedInitialization.qll
View File

@@ -699,11 +699,11 @@ abstract class TranslatedElementInitialization extends TranslatedElement {
abstract int getElementIndex();
final InstructionTag getElementAddressTag() {
result = InitializerElementAddressTag(getElementIndex())
result = InitializerElementAddressTag()
}
final InstructionTag getElementIndexTag() {
result = InitializerElementIndexTag(getElementIndex())
result = InitializerElementIndexTag()
}
final ArrayAggregateLiteral getInitList() {
@@ -861,11 +861,11 @@ class TranslatedElementValueInitialization extends TranslatedElementInitializati
}
private InstructionTag getElementDefaultValueTag() {
result = InitializerElementDefaultValueTag(elementIndex)
result = InitializerElementDefaultValueTag()
}
private InstructionTag getElementDefaultValueStoreTag() {
result = InitializerElementDefaultValueStoreTag(elementIndex)
result = InitializerElementDefaultValueStoreTag()
}
private Type getDefaultValueType() {

50
cpp/ql/test/library-tests/ir/ir/PrintAST.expected
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@@ -6,6 +6,10 @@
#-----| params:
#-----| 0: [Parameter] p#0
#-----| Type = [RValueReferenceType] __va_list_tag &&
#-----| [Operator,TopLevelFunction] void operator delete(void*)
#-----| params:
#-----| 0: [Parameter] p#0
#-----| Type = [VoidPointerType] void *
#-----| [Operator,TopLevelFunction] void operator delete(void*, unsigned long)
#-----| params:
#-----| 0: [Parameter] p#0
@@ -8001,3 +8005,49 @@ ir.cpp:
# 1147| 2: [Handler] <handler>
# 1147| 0: [CatchBlock] { ... }
# 1149| 1: [ReturnStmt] return ...
perf-regression.cpp:
# 4| [CopyAssignmentOperator] Big& Big::operator=(Big const&)
# 4| params:
#-----| 0: [Parameter] p#0
#-----| Type = [LValueReferenceType] const Big &
# 4| [MoveAssignmentOperator] Big& Big::operator=(Big&&)
# 4| params:
#-----| 0: [Parameter] p#0
#-----| Type = [RValueReferenceType] Big &&
# 4| [CopyConstructor] void Big::Big(Big const&)
# 4| params:
#-----| 0: [Parameter] p#0
#-----| Type = [LValueReferenceType] const Big &
# 4| [MoveConstructor] void Big::Big(Big&&)
# 4| params:
#-----| 0: [Parameter] p#0
#-----| Type = [RValueReferenceType] Big &&
# 6| [Constructor] void Big::Big()
# 6| params:
# 6| initializations:
# 6| 0: [ConstructorFieldInit] constructor init of field buffer
# 6| Type = [ArrayType] char[1073741824]
# 6| ValueCategory = prvalue
# 6| 0: [ArrayAggregateLiteral] {...}
# 6| Type = [ArrayType] char[1073741824]
# 6| ValueCategory = prvalue
# 6| body: [Block] { ... }
# 6| 0: [ReturnStmt] return ...
# 9| [TopLevelFunction] int main()
# 9| params:
# 9| body: [Block] { ... }
# 10| 0: [DeclStmt] declaration
# 10| 0: [VariableDeclarationEntry] definition of big
# 10| Type = [PointerType] Big *
# 10| init: [Initializer] initializer for big
# 10| expr: [NewExpr] new
# 10| Type = [PointerType] Big *
# 10| ValueCategory = prvalue
# 10| 1: [ConstructorCall] call to Big
# 10| Type = [VoidType] void
# 10| ValueCategory = prvalue
# 12| 1: [ReturnStmt] return ...
# 12| 0: [Literal,Zero] 0
# 12| Type = [IntType] int
# 12| Value = [Literal,Zero] 0
# 12| ValueCategory = prvalue

13
cpp/ql/test/library-tests/ir/ir/perf-regression.cpp Normal file
View File

@@ -0,0 +1,13 @@
// This test ensures that we can efficiently generate IR for a large
// value-initialized array.
struct Big {
char buffer[1 << 30]; // 1 GiB
Big() : buffer() {} // This explicit init of `buffer` makes it value-initialized
};
int main() {
Big *big = new Big;
return 0;
}

40
cpp/ql/test/library-tests/ir/ir/raw_ir.expected
View File

@@ -5269,3 +5269,43 @@ ir.cpp:
# 1149| v13_0(void) = NoOp :
# 1133| v13_1(void) = ReturnVoid :
#-----| Goto -> Block 1
perf-regression.cpp:
# 6| void Big::Big()
# 6| Block 0
# 6| v0_0(void) = EnterFunction :
# 6| mu0_1(unknown) = AliasedDefinition :
# 6| mu0_2(unknown) = UnmodeledDefinition :
# 6| r0_3(glval<Big>) = InitializeThis :
# 6| r0_4(glval<char[1073741824]>) = FieldAddress[buffer] : r0_3
# 6| r0_5(int) = Constant[0] :
# 6| r0_6(glval<char>) = PointerAdd : r0_4, r0_5
# 6| r0_7(unknown[1073741824]) = Constant[0] :
# 6| mu0_8(unknown[1073741824]) = Store : &:r0_6, r0_7
# 6| v0_9(void) = NoOp :
# 6| v0_10(void) = ReturnVoid :
# 6| v0_11(void) = UnmodeledUse : mu*
# 6| v0_12(void) = ExitFunction :
# 9| int main()
# 9| Block 0
# 9| v0_0(void) = EnterFunction :
# 9| mu0_1(unknown) = AliasedDefinition :
# 9| mu0_2(unknown) = UnmodeledDefinition :
# 10| r0_3(glval<Big *>) = VariableAddress[big] :
# 10| r0_4(glval<unknown>) = FunctionAddress[operator new] :
# 10| r0_5(unsigned long) = Constant[1073741824] :
# 10| r0_6(void *) = Call : func:r0_4, 0:r0_5
# 10| mu0_7(unknown) = ^CallSideEffect : ~mu0_2
# 10| r0_8(Big *) = Convert : r0_6
# 10| r0_9(glval<unknown>) = FunctionAddress[Big] :
# 10| v0_10(void) = Call : func:r0_9, this:r0_8
# 10| mu0_11(unknown) = ^CallSideEffect : ~mu0_2
# 10| mu0_12(Big *) = Store : &:r0_3, r0_8
# 12| r0_13(glval<int>) = VariableAddress[#return] :
# 12| r0_14(int) = Constant[0] :
# 12| mu0_15(int) = Store : &:r0_13, r0_14
# 9| r0_16(glval<int>) = VariableAddress[#return] :
# 9| v0_17(void) = ReturnValue : &:r0_16, ~mu0_2
# 9| v0_18(void) = UnmodeledUse : mu*
# 9| v0_19(void) = ExitFunction :

1
cpp/ql/test/library-tests/literals/aggregate_literals/arrays_value_init.ql
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@@ -2,5 +2,6 @@ import cpp
from ArrayType a, ArrayAggregateLiteral al, int i
where a = al.getType()
and i = [0 .. al.getUnspecifiedType().(ArrayType).getArraySize()]
and al.isValueInitialized(i)
select al, a, i