From C11 and C++11 onwards, a forward-progress requirement has been
introduced for both languages. In the case of C, loops with non-constant
conditionals that do not have any observable side-effects (as defined by
6.8.5p6) can be assumed by the implementation to terminate, and in the
case of C++, this assumption extends to all functions. The clang
frontend will emit the `mustprogress` function attribute for C++
functions (D86233, D85393, D86841) and emit the loop metadata
`llvm.loop.mustprogress` for every loop in C11 or later that has a
non-constant conditional.
This patch modifies LoopDeletion so that only loops with
the `llvm.loop.mustprogress` metadata or loops contained in functions
that are required to make progress (`mustprogress` or `willreturn`) are
checked for observable side-effects. If these loops do not have an
observable side-effect, then we delete them.
Loops without observable side-effects that do not satisfy the above
conditions will not be deleted.
Reviewed By: jdoerfert
Differential Revision: https://reviews.llvm.org/D86844
-print-after IR printing generally can not print the IR unit (Loop or SCC)
which has just been invalidated by the pass. However, when working in -print-module-scope
mode even if Loop was invalidated there is still a valid module that we can print.
Since we can not access invalidated IR unit from AfterPassInvalidated instrumentation
point we can remember the module to be printed *before* pass. This change introduces
BeforePass instrumentation that stores all the information required for module printing
into the stack and then after pass (in AfterPassInvalidated) just print whatever
has been placed on stack.
Reviewed By: philip.pfaffe
Differential Revision: https://reviews.llvm.org/D55278
llvm-svn: 349896
IR-printing AfterPass instrumentation might be called on a loop
that has just been invalidated. We should skip printing it to
avoid spurious asserts.
Reviewed By: chandlerc, philip.pfaffe
Differential Revision: https://reviews.llvm.org/D54740
llvm-svn: 348887
Atmn Patel