When deleting operations in DCE, the algorithm uses a post-order walk of
the IR to ensure that value uses were erased before value defs. Graph
regions do not have the same structural invariants as SSA CFG, and this
post order walk could delete value defs before uses.  This problem is
guaranteed to occur when there is a cycle in the use-def graph.

This change stops DCE from visiting the operations and blocks in any
meaningful order.  Instead, we rely on explicitly dropping all uses of a
value before deleting it.

Reviewed By: mehdi_amini, rriddle

Differential Revision: https://reviews.llvm.org/D98919

This does not split transformations, yet. Those will be done as future clean ups.

Differential Revision: https://reviews.llvm.org/D96272

This option avoids to accidentally reuse variable across -LABEL match,
it can be explicitly opted-in by prefixing the variable name with $

Differential Revision: https://reviews.llvm.org/D81531

This revision adds support for merging identical blocks, or those with the same operations that branch to the same successors. Operands that mismatch between the different blocks are replaced with new block arguments added to the merged block.

Differential Revision: https://reviews.llvm.org/D79134

Differential Revision: https://reviews.llvm.org/D76903

Summary:
This revision removes all of the functionality related to successor operands on the core Operation class. This greatly simplifies a lot of handling of operands, as well as successors. For example, DialectConversion no longer needs a special "matchAndRewrite" for branching terminator operations.(Note, the existing method was also broken for operations with variadic successors!!)

This also enables terminator operations to define their own relationships with successor arguments, instead of the hardcoded "pass-through" behavior that exists today.

Differential Revision: https://reviews.llvm.org/D75318

This moves the different canonicalizations of regions into one place and invokes them in the fixed-point iteration of the canonicalizer.

PiperOrigin-RevId: 281617072

This is a simple multi-level DCE pass that operates pretty generically on
the IR. Its key feature compared to the existing peephole dead op folding
that happens during canonicalization is being able to delete recursively
dead cycles of the use-def graph, including block arguments.

PiperOrigin-RevId: 281568202