[llvm] [CodeGen][AMDGPU] Replace isBasicBlockPrologue with a MachineInstr::BBProlog flag (PR #225433)

[Gabriel Baraldi via llvm-commits]

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@@ -210,13 +210,22 @@ MachineBasicBlock::iterator MachineBasicBlock::getFirstNonPHI() {
   return I;
 }
 
+void MachineBasicBlock::inheritBBProlog(iterator Begin, iterator End) {
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gbaraldi wrote:

I added a new version of this that mostly checks and then sets explicitly 

https://github.com/llvm/llvm-project/pull/225433