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C++: Output CopyValue in the IR when there is a non-transparent conversion #19976

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C++: Output CopyValue in the IR when there is a non-transparent conversion #19976

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799f33e
C++: Add more postfix-crement tests
jketema Jul 4, 2025
e68d101
C++: Fix typo in comment
jketema Jul 4, 2025
b185cc8
C++: Factor out transparent conversions in their own predicate
jketema Jul 4, 2025
2908570
C++: Do not consider expression results discardable when there is a c…
jketema Jul 4, 2025
d010b6e
C++: Update expected test results
jketema Jul 4, 2025
463ae4b
C++: Address review comments
jketema Jul 4, 2025
d6d7c6d
Revert "C++: Factor out transparent conversions in their own predicate"
jketema Jul 4, 2025
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2 changes: 1 addition & 1 deletion cpp/ql/lib/semmle/code/cpp/ir/dataflow/internal/ExprNodes.qll
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Expand Up @@ -151,7 +151,7 @@ private module Cached {
)
or
// Similarly for `i++` and `++i` we pretend that the generated
// `StoreInstruction` is contains the result of the expression even though
// `StoreInstruction` contains the result of the expression even though
// this isn't totally aligned with the C/C++ standard.
exists(TranslatedCrementOperation tco |
store = tco.getInstruction(CrementStoreTag()) and
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19 changes: 10 additions & 9 deletions cpp/ql/lib/semmle/code/cpp/ir/implementation/raw/internal/TranslatedExpr.qll
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Expand Up @@ -909,17 +909,17 @@ class TranslatedTransparentUnaryOperation extends TranslatedTransparentExpr {
}
}

private predicate isTransparentConversion(Conversion expr) {
expr instanceof ParenthesisExpr or
expr instanceof ReferenceDereferenceExpr or
expr instanceof ReferenceToExpr or
expr instanceof C11GenericExpr
}

class TranslatedTransparentConversion extends TranslatedTransparentExpr {
override Conversion expr;

TranslatedTransparentConversion() {
(
expr instanceof ParenthesisExpr or
expr instanceof ReferenceDereferenceExpr or
expr instanceof ReferenceToExpr or
expr instanceof C11GenericExpr
)
}
TranslatedTransparentConversion() { isTransparentConversion(expr) }

override TranslatedExpr getOperand() { result = getTranslatedExpr(expr.getExpr()) }
}
Expand Down Expand Up @@ -4146,7 +4146,8 @@ predicate exprNeedsCopyIfNotLoaded(Expr expr) {
private predicate exprImmediatelyDiscarded(Expr expr) {
exists(ExprStmt s |
s = expr.getParent() and
not exists(StmtExpr se | s = se.getStmt().(BlockStmt).getLastStmt())
not exists(StmtExpr se | s = se.getStmt().(BlockStmt).getLastStmt()) and
not exists(Conversion c | c = expr.getConversion*() and not isTransparentConversion(c))
)
or
exists(CommaExpr c | c.getLeftOperand() = expr)
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12 changes: 10 additions & 2 deletions cpp/ql/test/library-tests/dataflow/asExpr/test.cpp
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Expand Up @@ -42,8 +42,16 @@ void test_aggregate_literal() {
void test_postfix_crement(int *p, int q) {
p++; // $ asExpr="... ++" asIndirectExpr="... ++" asExpr=p asIndirectExpr=p
q++; // $ asExpr="... ++" asExpr=q
(void)(p++); // $ numberOfNodes="... ++: 2" asExpr="... ++" numberOfIndirectNodes="... ++: 2" asIndirectExpr="... ++" MISSING: asExpr=p asIndirectExpr=p
(void)(q++); // $ numberOfNodes="... ++: 2" asExpr="... ++" MISSING: asExpr=q
(p++); // $ numberOfNodes="... ++: 2" numberOfIndirectNodes="... ++: 2" asExpr="... ++" asIndirectExpr="... ++"
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I'm a bit confused by this one. As far as I tell you've deleted the MISSING annotations and since CI still pass I guess they're still missing, no?

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I should also say: The other changes makes sense to me!

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I should have looked at the results better. I thought it would just work, because the IR looks identical to that of the two lines above it. If I also generate the CopyValue in this case, then things work.

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Fix 463ae4b Re-running DCA.

(q++); // $ numberOfNodes="... ++: 2" asExpr="... ++"
(void)(p++); // $ asExpr="p(... ++)" asIndirectExpr="p(*... ++)"
(void)(q++); // $ asExpr="q(... ++)"
(void)p++; // $ asExpr="p(... ++)" asIndirectExpr="p(*... ++)"
(void)q++; // $ asExpr="q(... ++)"
int *p1 = p++; // $ asExpr="... ++" asIndirectExpr="... ++" asExpr="p(... ++)" asIndirectExpr="p(*... ++)"
int q1 = q++; // $ asExpr="... ++" asExpr="q(... ++)"
(int*)(p++); // $ asExpr="... ++" asIndirectExpr="... ++" asExpr="p(... ++)" asIndirectExpr="p(*... ++)"
(int)(q++); // $ asExpr="... ++" asExpr="q(... ++)"
int *p2 = (int*)(p++); // $ asExpr="... ++" asIndirectExpr="... ++" asExpr="p(... ++)" asIndirectExpr="p(*... ++)"
int q2 = (int)(q++); // $ asExpr="... ++" asExpr="q(... ++)"
}
174 changes: 174 additions & 0 deletions cpp/ql/test/library-tests/ir/ir/PrintAST.expected
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Expand Up @@ -24262,6 +24262,180 @@ ir.cpp:
# 2725| getExpr().getFullyConverted(): [ReferenceDereferenceExpr] (reference dereference)
# 2725| Type = [PlainCharType] char
# 2725| ValueCategory = prvalue(load)
# 2728| [TopLevelFunction] void test_postfix_crement(int*, int)
# 2728| <params>:
# 2728| getParameter(0): [Parameter] p
# 2728| Type = [IntPointerType] int *
# 2728| getParameter(1): [Parameter] q
# 2728| Type = [IntType] int
# 2728| getEntryPoint(): [BlockStmt] { ... }
# 2729| getStmt(0): [ExprStmt] ExprStmt
# 2729| getExpr(): [PostfixIncrExpr] ... ++
# 2729| Type = [IntPointerType] int *
# 2729| ValueCategory = prvalue
# 2729| getOperand(): [VariableAccess] p
# 2729| Type = [IntPointerType] int *
# 2729| ValueCategory = lvalue
# 2730| getStmt(1): [ExprStmt] ExprStmt
# 2730| getExpr(): [PostfixIncrExpr] ... ++
# 2730| Type = [IntType] int
# 2730| ValueCategory = prvalue
# 2730| getOperand(): [VariableAccess] q
# 2730| Type = [IntType] int
# 2730| ValueCategory = lvalue
# 2731| getStmt(2): [ExprStmt] ExprStmt
# 2731| getExpr(): [PostfixIncrExpr] ... ++
# 2731| Type = [IntPointerType] int *
# 2731| ValueCategory = prvalue
# 2731| getOperand(): [VariableAccess] p
# 2731| Type = [IntPointerType] int *
# 2731| ValueCategory = lvalue
# 2731| getExpr().getFullyConverted(): [ParenthesisExpr] (...)
# 2731| Type = [IntPointerType] int *
# 2731| ValueCategory = prvalue
# 2732| getStmt(3): [ExprStmt] ExprStmt
# 2732| getExpr(): [PostfixIncrExpr] ... ++
# 2732| Type = [IntType] int
# 2732| ValueCategory = prvalue
# 2732| getOperand(): [VariableAccess] q
# 2732| Type = [IntType] int
# 2732| ValueCategory = lvalue
# 2732| getExpr().getFullyConverted(): [ParenthesisExpr] (...)
# 2732| Type = [IntType] int
# 2732| ValueCategory = prvalue
# 2733| getStmt(4): [ExprStmt] ExprStmt
# 2733| getExpr(): [PostfixIncrExpr] ... ++
# 2733| Type = [IntPointerType] int *
# 2733| ValueCategory = prvalue
# 2733| getOperand(): [VariableAccess] p
# 2733| Type = [IntPointerType] int *
# 2733| ValueCategory = lvalue
# 2733| getExpr().getFullyConverted(): [CStyleCast] (void)...
# 2733| Conversion = [VoidConversion] conversion to void
# 2733| Type = [VoidType] void
# 2733| ValueCategory = prvalue
# 2733| getExpr(): [ParenthesisExpr] (...)
# 2733| Type = [IntPointerType] int *
# 2733| ValueCategory = prvalue
# 2734| getStmt(5): [ExprStmt] ExprStmt
# 2734| getExpr(): [PostfixIncrExpr] ... ++
# 2734| Type = [IntType] int
# 2734| ValueCategory = prvalue
# 2734| getOperand(): [VariableAccess] q
# 2734| Type = [IntType] int
# 2734| ValueCategory = lvalue
# 2734| getExpr().getFullyConverted(): [CStyleCast] (void)...
# 2734| Conversion = [VoidConversion] conversion to void
# 2734| Type = [VoidType] void
# 2734| ValueCategory = prvalue
# 2734| getExpr(): [ParenthesisExpr] (...)
# 2734| Type = [IntType] int
# 2734| ValueCategory = prvalue
# 2735| getStmt(6): [ExprStmt] ExprStmt
# 2735| getExpr(): [PostfixIncrExpr] ... ++
# 2735| Type = [IntPointerType] int *
# 2735| ValueCategory = prvalue
# 2735| getOperand(): [VariableAccess] p
# 2735| Type = [IntPointerType] int *
# 2735| ValueCategory = lvalue
# 2735| getExpr().getFullyConverted(): [CStyleCast] (void)...
# 2735| Conversion = [VoidConversion] conversion to void
# 2735| Type = [VoidType] void
# 2735| ValueCategory = prvalue
# 2736| getStmt(7): [ExprStmt] ExprStmt
# 2736| getExpr(): [PostfixIncrExpr] ... ++
# 2736| Type = [IntType] int
# 2736| ValueCategory = prvalue
# 2736| getOperand(): [VariableAccess] q
# 2736| Type = [IntType] int
# 2736| ValueCategory = lvalue
# 2736| getExpr().getFullyConverted(): [CStyleCast] (void)...
# 2736| Conversion = [VoidConversion] conversion to void
# 2736| Type = [VoidType] void
# 2736| ValueCategory = prvalue
# 2737| getStmt(8): [DeclStmt] declaration
# 2737| getDeclarationEntry(0): [VariableDeclarationEntry] definition of p1
# 2737| Type = [IntPointerType] int *
# 2737| getVariable().getInitializer(): [Initializer] initializer for p1
# 2737| getExpr(): [PostfixIncrExpr] ... ++
# 2737| Type = [IntPointerType] int *
# 2737| ValueCategory = prvalue
# 2737| getOperand(): [VariableAccess] p
# 2737| Type = [IntPointerType] int *
# 2737| ValueCategory = lvalue
# 2738| getStmt(9): [DeclStmt] declaration
# 2738| getDeclarationEntry(0): [VariableDeclarationEntry] definition of q1
# 2738| Type = [IntType] int
# 2738| getVariable().getInitializer(): [Initializer] initializer for q1
# 2738| getExpr(): [PostfixIncrExpr] ... ++
# 2738| Type = [IntType] int
# 2738| ValueCategory = prvalue
# 2738| getOperand(): [VariableAccess] q
# 2738| Type = [IntType] int
# 2738| ValueCategory = lvalue
# 2739| getStmt(10): [ExprStmt] ExprStmt
# 2739| getExpr(): [PostfixIncrExpr] ... ++
# 2739| Type = [IntPointerType] int *
# 2739| ValueCategory = prvalue
# 2739| getOperand(): [VariableAccess] p
# 2739| Type = [IntPointerType] int *
# 2739| ValueCategory = lvalue
# 2739| getExpr().getFullyConverted(): [CStyleCast] (int *)...
# 2739| Conversion = [PointerConversion] pointer conversion
# 2739| Type = [IntPointerType] int *
# 2739| ValueCategory = prvalue
# 2739| getExpr(): [ParenthesisExpr] (...)
# 2739| Type = [IntPointerType] int *
# 2739| ValueCategory = prvalue
# 2740| getStmt(11): [ExprStmt] ExprStmt
# 2740| getExpr(): [PostfixIncrExpr] ... ++
# 2740| Type = [IntType] int
# 2740| ValueCategory = prvalue
# 2740| getOperand(): [VariableAccess] q
# 2740| Type = [IntType] int
# 2740| ValueCategory = lvalue
# 2740| getExpr().getFullyConverted(): [CStyleCast] (int)...
# 2740| Conversion = [IntegralConversion] integral conversion
# 2740| Type = [IntType] int
# 2740| ValueCategory = prvalue
# 2740| getExpr(): [ParenthesisExpr] (...)
# 2740| Type = [IntType] int
# 2740| ValueCategory = prvalue
# 2741| getStmt(12): [DeclStmt] declaration
# 2741| getDeclarationEntry(0): [VariableDeclarationEntry] definition of p2
# 2741| Type = [IntPointerType] int *
# 2741| getVariable().getInitializer(): [Initializer] initializer for p2
# 2741| getExpr(): [PostfixIncrExpr] ... ++
# 2741| Type = [IntPointerType] int *
# 2741| ValueCategory = prvalue
# 2741| getOperand(): [VariableAccess] p
# 2741| Type = [IntPointerType] int *
# 2741| ValueCategory = lvalue
# 2741| getExpr().getFullyConverted(): [CStyleCast] (int *)...
# 2741| Conversion = [PointerConversion] pointer conversion
# 2741| Type = [IntPointerType] int *
# 2741| ValueCategory = prvalue
# 2741| getExpr(): [ParenthesisExpr] (...)
# 2741| Type = [IntPointerType] int *
# 2741| ValueCategory = prvalue
# 2742| getStmt(13): [DeclStmt] declaration
# 2742| getDeclarationEntry(0): [VariableDeclarationEntry] definition of q2
# 2742| Type = [IntType] int
# 2742| getVariable().getInitializer(): [Initializer] initializer for q2
# 2742| getExpr(): [PostfixIncrExpr] ... ++
# 2742| Type = [IntType] int
# 2742| ValueCategory = prvalue
# 2742| getOperand(): [VariableAccess] q
# 2742| Type = [IntType] int
# 2742| ValueCategory = lvalue
# 2742| getExpr().getFullyConverted(): [CStyleCast] (int)...
# 2742| Conversion = [IntegralConversion] integral conversion
# 2742| Type = [IntType] int
# 2742| ValueCategory = prvalue
# 2742| getExpr(): [ParenthesisExpr] (...)
# 2742| Type = [IntType] int
# 2742| ValueCategory = prvalue
# 2743| getStmt(14): [ReturnStmt] return ...
ir23.cpp:
# 1| [TopLevelFunction] bool consteval_1()
# 1| <params>:
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