[llvm] [AMDGPU][MC] Disallow null as saddr in flat instructions (PR #101730)

[Matt Arsenault via llvm-commits]

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@@ -6205,6 +6205,12 @@ void SIInstrInfo::legalizeOperandsFLAT(MachineRegisterInfo &MRI,
     return;
 
   Register ToSGPR = readlaneVGPRToSGPR(SAddr->getReg(), MI, MRI);
+
+  const TargetRegisterClass *DeclaredRC =
+      getRegClass(MI.getDesc(), SAddr->getOperandNo(),
+                  MRI.getTargetRegisterInfo(), *MI.getParent()->getParent());
+
+  MRI.setRegClass(ToSGPR, DeclaredRC);
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arsenm wrote:

Something like this, (but you can just use RI directly as a member of SIInstrInfo)

Also it's easier to review changes when you post them as real revisions 

https://github.com/llvm/llvm-project/pull/101730