[llvm] [AMDGPU]: Add implicit-def to the BB prolog (PR #112872)

[Christudasan Devadasan via llvm-commits]

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@@ -8918,6 +8918,7 @@ bool SIInstrInfo::isBasicBlockPrologue(const MachineInstr &MI,
   uint16_t Opcode = MI.getOpcode();
   return IsNullOrVectorRegister &&
          (isSGPRSpill(Opcode) || isWWMRegSpillOpcode(Opcode) ||
+          Opcode == AMDGPU::IMPLICIT_DEF ||
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cdevadas wrote:

I had the same thought initially. But we add implicit-def for other different cases and they can break the BB prolog too.
They are hard to track if such edge cases occur. This fix looks much better in that way. 

https://github.com/llvm/llvm-project/pull/112872