phiopt: Use remove_phi_node for efficiency
Replaces `gsi_remove` with `remove_phi_node` in the phiopt pass for better memory management of PHI nodes.
The phiopt optimization pass in GCC has been refactored to use remove_phi_node instead of gsi_remove when processing PHI nodes. This change ensures that PHI nodes are immediately freed or made available for reuse, rather than remaining in memory until the next garbage collection cycle. This improves the efficiency of the phiopt pass.
In Details
This commit replaces calls to gsi_remove with remove_phi_node in factor_out_conditional_operation and factor_out_conditional_load within the phiopt pass. The former leaves the PHI node allocated, leading to delayed garbage collection. remove_phi_node, when called with false (indicating the PHI node's result is still used), correctly removes the PHI node from the GSI graph while ensuring its resources are managed efficiently.
- PHI node
- A node in Static Single Assignment (SSA) form that represents the merging of values from different control flow paths. It determines which value to use based on which path was taken to reach the node.
- SSA form
- Static Single Assignment form is an intermediate representation property where each variable is assigned a value exactly once. This simplifies many compiler optimizations.
- phiopt
- An optimization pass in GCC that focuses on simplifying and optimizing PHI nodes in the SSA representation.
- gsi_remove
- A function in GCC's internal representation often used to remove an instruction or node from the instruction stream without necessarily freeing its associated data structures immediately.
- remove_phi_node
- A specific function in GCC's SSA infrastructure designed to correctly remove a PHI node from the graph, managing its associated memory and data structures.