Skip to content

Fix for #1026: Enabling LifetimeEnds CFGElement crashes the compiler during CFG construction #1028

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
sulekhark merged 4 commits into from
Apr 16, 2021
Merged

Fix for #1026: Enabling LifetimeEnds CFGElement crashes the compiler during CFG construction #1028

Show file tree
Hide file tree
Changes from 3 commits
Commits
Show all changes
4 commits
Select commit Hold shift + click to select a range
8ff45c1
Fix for the crash during CFG construction when CFGLifetimeEnds elemen…
sulekhark Apr 12, 2021
0158977
Merge branch 'master' into lifetime_ends_cfg_elem
sulekhark Apr 12, 2021
5d33780
Merge branch 'master' into lifetime_ends_cfg_elem
sulekhark Apr 13, 2021
ec2752a
Incorporated review comments.
sulekhark Apr 16, 2021
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
19 changes: 17 additions & 2 deletions clang/lib/Analysis/CFG.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -2085,9 +2085,24 @@ void CFGBuilder::prependAutomaticObjLifetimeWithTerminator(
if (!BuildOpts.AddLifetime)
return;
BumpVectorContext &C = cfg->getBumpVectorContext();

// Note that B is the LocalScope iterator associated with the backpatched
// jump and E is the LocalScope iterator associated with the jump target.
//
// To go from B to E, one first goes up the scopes from B
// to PofB, then sideways in one scope from PofB to PofE and then down
// the scopes from PofE to E.
// The lifetime of all objects between B and PofE end.
//
// Get E's ancestor that has the same LocalScope as one of B's ancestors.
LocalScope::const_iterator PofE = E.shared_parent(B);
int Dist = B.distance(PofE);
if (Dist <= 0)

@mgrang mgrang Apr 13, 2021

Copy link
Copy Markdown

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Can the distance be less than 0?

@sulekhark sulekhark Apr 13, 2021

Copy link
Copy Markdown
Contributor Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

While Dist cannot be less than 0 if the distance function is called as intended, it is possible to provide arguments to it such that the distance between two LocalScope iterators is less than zero. For example, this can happen if the control comes here for a "forward" jumping goto statement (which should not ideally happen). Moreover, this kind of check is there in two other places too and they have used a <= check (see lines 1770 - 1777).

return;

CFGBlock::iterator InsertPos =
Blk->beginLifetimeEndsInsert(Blk->end(), B.distance(E), C);
for (LocalScope::const_iterator I = B; I != E; ++I) {
Blk->beginLifetimeEndsInsert(Blk->end(), Dist, C);
for (LocalScope::const_iterator I = B; I != PofE; ++I) {
InsertPos =
Blk->insertLifetimeEnds(InsertPos, *I, Blk->getTerminatorStmt());
}
Expand Down
156 changes: 156 additions & 0 deletions clang/test/Analysis/lifetime-cfg-output.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -781,3 +781,159 @@ int backpatched_goto() {
goto label;
i++;
}

extern int bar(char *s, int n);

// CHECK: [B3 (ENTRY)]
// CHECK-NEXT: Succs (1): B2
// CHECK: [B1]
// CHECK-NEXT: label:
// CHECK-NEXT: 1: bar
// CHECK-NEXT: 2: [B1.1] (ImplicitCastExpr, FunctionToPointerDecay, int (*)(char *, int))
// CHECK-NEXT: 3: x
// CHECK-NEXT: 4: &[B1.3]
// CHECK-NEXT: 5: 1
// CHECK-NEXT: 6: [B1.2]([B1.4], [B1.5])
// CHECK-NEXT: 7: [B2.1] (Lifetime ends)
// CHECK-NEXT: T: goto label;
// CHECK-NEXT: Preds (2): B2 B1
// CHECK-NEXT: Succs (1): B1
// CHECK: [B2]
// CHECK-NEXT: 1: char x;
// CHECK-NEXT: Preds (1): B3
// CHECK-NEXT: Succs (1): B1
// CHECK: [B0 (EXIT)]

// test case from CodeGen/lifetime2.c
void backpatched_goto1() {
{
char x;
label:
bar(&x, 1);
}
goto label;
}


// CHECK: [B4 (ENTRY)]
// CHECK-NEXT: Succs (1): B3
// CHECK: [B1]
// CHECK-NEXT: 1: [B2.2] (Lifetime ends)
// CHECK-NEXT: Succs (1): B0
// CHECK: [B2]
// CHECK-NEXT: 1: (CXXConstructExpr, struct B)
// CHECK-NEXT: 2: B c;
// CHECK-NEXT: 3: [B2.2] (Lifetime ends)
// CHECK-NEXT: T: goto label;
// CHECK-NEXT: Preds (1): B3
// CHECK-NEXT: Succs (1): B3
// CHECK: [B3]
// CHECK-NEXT: label:
// CHECK-NEXT: 1: (CXXConstructExpr, struct B)
// CHECK-NEXT: 2: B b;
// CHECK-NEXT: 3: [B3.2] (Lifetime ends)
// CHECK-NEXT: 4: 1
// CHECK-NEXT: 5: [B3.4] (ImplicitCastExpr, IntegralToBoolean, _Bool)
// CHECK-NEXT: T: if [B3.5]
// CHECK-NEXT: Preds (2): B2 B4
// CHECK-NEXT: Succs (2): B2 B0(Unreachable)
// CHECK: [B0 (EXIT)]
// CHECK-NEXT: Preds (2): B1 B3(Unreachable)

int backpatched_goto2() {
{
label:
B b;
}
if (1){
B c;
goto label;
}
}


// The two test cases below illustrate the need to traverse up
// the tree of nested scopes to find the nearest common ancestor.

// CHECK: [B4 (ENTRY)]
// CHECK-NEXT: Succs (1): B3
// CHECK: [B1]
// CHECK-NEXT: 1: [B2.9] (Lifetime ends)
// CHECK-NEXT: Succs (1): B0
// CHECK: [B2]
// CHECK-NEXT: label:
// CHECK-NEXT: 1: bar
// CHECK-NEXT: 2: [B2.1] (ImplicitCastExpr, FunctionToPointerDecay, int (*)(char *, int))
// CHECK-NEXT: 3: x
// CHECK-NEXT: 4: &[B2.3]
// CHECK-NEXT: 5: 1
// CHECK-NEXT: 6: [B2.2]([B2.4], [B2.5])
// CHECK-NEXT: 7: [B3.1] (Lifetime ends)
// CHECK-NEXT: 8: (CXXConstructExpr, struct B)
// CHECK-NEXT: 9: B b;
// CHECK-NEXT: 10: [B2.9] (Lifetime ends)
// CHECK-NEXT: T: goto label;
// CHECK-NEXT: Preds (2): B3 B2
// CHECK-NEXT: Succs (1): B2
// CHECK: [B3]
// CHECK-NEXT: 1: char x;
// CHECK-NEXT: Preds (1): B4
// CHECK-NEXT: Succs (1): B2
// CHECK: [B0 (EXIT)]
// CHECK-NEXT: Preds (1): B1

void backpatched_goto3() {
{
char x;
label:
bar(&x, 1);
}
{
B b;
goto label;
}
}

// CHECK: [B4 (ENTRY)]
// CHECK-NEXT: Succs (1): B3
// CHECK: [B1]
// CHECK-NEXT: 1: [B2.11] (Lifetime ends)
// CHECK-NEXT: 2: [B2.9] (Lifetime ends)
// CHECK-NEXT: Succs (1): B0
// CHECK: [B2]
// CHECK-NEXT: label:
// CHECK-NEXT: 1: bar
// CHECK-NEXT: 2: [B2.1] (ImplicitCastExpr, FunctionToPointerDecay, int (*)(char *, int))
// CHECK-NEXT: 3: x
// CHECK-NEXT: 4: &[B2.3]
// CHECK-NEXT: 5: 1
// CHECK-NEXT: 6: [B2.2]([B2.4], [B2.5])
// CHECK-NEXT: 7: [B3.1] (Lifetime ends)
// CHECK-NEXT: 8: (CXXConstructExpr, struct B)
// CHECK-NEXT: 9: B c;
// CHECK-NEXT: 10: (CXXConstructExpr, struct B)
// CHECK-NEXT: 11: B b;
// CHECK-NEXT: 12: [B2.11] (Lifetime ends)
// CHECK-NEXT: 13: [B2.9] (Lifetime ends)
// CHECK-NEXT: T: goto label;
// CHECK-NEXT: Preds (2): B3 B2
// CHECK-NEXT: Succs (1): B2
// CHECK: [B3]
// CHECK-NEXT: 1: char x;
// CHECK-NEXT: Preds (1): B4
// CHECK-NEXT: Succs (1): B2
// CHECK: [B0 (EXIT)]
// CHECK-NEXT: Preds (1): B1

void backpatched_goto4() {
{
char x;
label:
bar(&x, 1);
}
B c;
{
B b;
goto label;
}
}