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Author SHA1 Message Date
Ilya Leoshkevich d58f112ce0 Prevent FENTRY_CALL reordering
FEntryInserter prepends FENTRY_CALL to the first basic block. In case
there are other instructions, PostRA Machine Instruction Scheduler can
move FENTRY_CALL call around. This actually occurs on SystemZ (see the
testcase). This is bad for the following reasons:

* FENTRY_CALL clobbers registers.
* Linux Kernel depends on whatever FENTRY_CALL expands to to be the very
  first instruction in the function.

Fix by adding isCall attribute to FENTRY_CALL, which prevents reordering
by making it a scheduling boundary for PostRA Machine Instruction
Scheduler.

Reviewed By: niravd

Differential Revision: https://reviews.llvm.org/D91218
2020-12-09 00:59:01 +01:00