Vettel dc1fadef23 [MCP] Enhance MCP copy Instruction removal for special case(reapply) (#74239) ...

Machine Copy Propagation Pass may lose some opportunities to further
remove the redundant copy instructions during the ForwardCopyPropagateBlock
procedure. When we Clobber a "Def" register, we also need to remove the record 
from the copy maps that indicates "Src" defined "Def" to ensure the correct semantics
of the ClobberRegister function.  This patch reapplies #70778 and addresses the corner 
case bug  #73512 specific to the AMDGPU backend. Additionally, it refines the criteria 
for removing empty records from the copy maps, thereby enhancing overall safety.

For more information, please see the C++ test case generated code in 
"vector.body" after the MCP Pass: https://gcc.godbolt.org/z/nK4oMaWv5.

2023-12-26 16:22:42 +08:00

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