This allows -polly-optree to move instructions that depend on
synthesizable values.
The difficulty for synthesizable values is that their value depends on
the location. When it is moved over a loop header, and the SCEV
expression depends on the loop induction variable (SCEVAddRecExpr), it
would use the current induction variable instead of the last one.
At the moment we cannot forward PHI nodes such that crossing the header
of loops referenced by SCEVAddRecExpr is not possible (assuming the loop
header has at least two incoming blocks: for entering the loop and the
backedge, such any instruction to be forwarded must have a phi between
use and definition).
A remaining issue is when the forwarded value is used after the loop,
but is only synthesizable inside the loop. This happens e.g. if
ScalarEvolution is unable to determine the number of loop iterations or
the initial loop value. We do not forward in this situation.
Differential Revision: https://reviews.llvm.org/D36102
llvm-svn: 309609
Read-only values (values defined before the SCoP) require special
handing with -polly-analyze-read-only-scalars=true (which is the
default). If active, each use of a value requires a read access.
When a copied value uses a read-only value, we must also ensure that
such a MemoryAccess is available or is created.
Differential Revision: https://reviews.llvm.org/D35764
llvm-svn: 308876
Hoisted loads can be trivially supported because there are no
MemoryAccess to be modified, the loaded value is just available
at code generation.
llvm-svn: 308826
This pass 'forwards' operand trees into statements that use them in
order to avoid scalar dependencies.
This minimal implementation handles only the case of speculatable
instructions. We will successively add support for:
- Hoisted loads
- Read-only values
- Synthesizable values
- Loads
- PHIs
- Forwarding only parts of the tree
Differential Revision: https://reviews.llvm.org/D35754
llvm-svn: 308825
Michael Kruse