[CodeGen] Suppress emission of lifetime markers if a label has been seen
in the current lexical scope.
clang currently emits the lifetime.start marker of a variable when the
variable comes into scope even though a variable's lifetime starts at
the entry of the block with which it is associated, according to the C
standard. This normally doesn't cause any problems, but in the rare case
where a goto jumps backwards past the variable declaration to an earlier
point in the block (see the test case added to lifetime2.c), it can
cause mis-compilation.
To prevent such mis-compiles, this commit conservatively disables
emitting lifetime variables when a label has been seen in the current
block.
This problem was discussed on cfe-dev here:
http://lists.llvm.org/pipermail/cfe-dev/2016-July/050066.html
rdar://problem/30153946
Differential Revision: https://reviews.llvm.org/D27680
llvm-svn: 293106
diff --git a/clang/lib/CodeGen/CGDecl.cpp b/clang/lib/CodeGen/CGDecl.cpp
index 0a88b23..b7c1743 100644
--- a/clang/lib/CodeGen/CGDecl.cpp
+++ b/clang/lib/CodeGen/CGDecl.cpp
@@ -1022,11 +1022,21 @@
// Emit a lifetime intrinsic if meaningful. There's no point in doing this
// if we don't have a valid insertion point (?).
if (HaveInsertPoint() && !IsMSCatchParam) {
- // goto or switch-case statements can break lifetime into several
- // regions which need more efforts to handle them correctly. PR28267
- // This is rare case, but it's better just omit intrinsics than have
- // them incorrectly placed.
- if (!Bypasses.IsBypassed(&D)) {
+ // If there's a jump into the lifetime of this variable, its lifetime
+ // gets broken up into several regions in IR, which requires more work
+ // to handle correctly. For now, just omit the intrinsics; this is a
+ // rare case, and it's better to just be conservatively correct.
+ // PR28267.
+ //
+ // We have to do this in all language modes if there's a jump past the
+ // declaration. We also have to do it in C if there's a jump to an
+ // earlier point in the current block because non-VLA lifetimes begin as
+ // soon as the containing block is entered, not when its variables
+ // actually come into scope; suppressing the lifetime annotations
+ // completely in this case is unnecessarily pessimistic, but again, this
+ // is rare.
+ if (!Bypasses.IsBypassed(&D) &&
+ !(!getLangOpts().CPlusPlus && hasLabelBeenSeenInCurrentScope())) {
uint64_t size = CGM.getDataLayout().getTypeAllocSize(allocaTy);
emission.SizeForLifetimeMarkers =
EmitLifetimeStart(size, address.getPointer());