[AMDGPU] Make overlaps with ScratchRSrcReg fatal errors

[critson]

Summary

Overlaps of these will always result in bad code.

[rampitec]

It seem to cause real test failures.

[critson]

In D81821#2092230, @rampitec wrote:

It seem to cause real test failures.

Currently investigating.
I was, for some reason, naive enough to think this would be fine.
Since the live-in overlap part is new, it'll be that.

[arsenm]

llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp

331

This should go in the verifier instead

331

There was a patch to add a target verifier hook for function level features, but I'm not sure it was ever committed

[critson]

Remove LiveIn parts.
I have concluded that they are wrong, or at least too complicated for a simple test.
In small functions parts of the ScratchRSrcReg may be formed from registers that
are live-ins, and these will work fine.

[arsenm]

llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp

339

This is only really an improvement for hand written MIR, and should go in the verifier?

[critson]

llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp

339

This can occur at compile time on LLVM IR with an -sgpr-limit set.

[arsenm]

llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp

339

Do you mean the attributes to directly limit the number of SGPRs? These should not be used anymore, and this is one of the reasons why.

llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp

BitVector SIRegisterInfo::getReservedRegs(const MachineFunction &MF) const {
   const SIMachineFunctionInfo *MFI = MF.getInfo<SIMachineFunctionInfo>();
 
   unsigned ScratchRSrcReg = MFI->getScratchRSrcReg();
   if (ScratchRSrcReg != AMDGPU::NoRegister) {
     // Reserve 4 SGPRs for the scratch buffer resource descriptor in case we need
     // to spill.
     // TODO: May need to reserve a VGPR if doing LDS spilling.
     reserveRegisterTuples(Reserved, ScratchRSrcReg);
   }
 
   // We have to assume the SP is needed in case there are calls in the function,
   // which is detected after the function is lowered. If we aren't really going
   // to need SP, don't bother reserving it.
   MCRegister StackPtrReg = MFI->getStackPtrOffsetReg();
 
   if (StackPtrReg) {
+    if (isSubRegister(ScratchRSrcReg, StackPtrReg))
+      report_fatal_error("scratch resource registers overlap stack pointer");
     reserveRegisterTuples(Reserved, StackPtrReg);
-    assert(!isSubRegister(ScratchRSrcReg, StackPtrReg));
   }
 
   MCRegister FrameReg = MFI->getFrameOffsetReg();
   if (FrameReg) {
+    if (isSubRegister(ScratchRSrcReg, FrameReg))
+      report_fatal_error("scratch resource registers overlap frame offset");
     reserveRegisterTuples(Reserved, FrameReg);
-    assert(!isSubRegister(ScratchRSrcReg, FrameReg));
   }
 
   if (hasBasePointer(MF)) {
     MCRegister BasePtrReg = getBaseRegister();
+    if (isSubRegister(ScratchRSrcReg, BasePtrReg))
+      report_fatal_error("scratch resource registers overlap base pointer");
     reserveRegisterTuples(Reserved, BasePtrReg);
-    assert(!isSubRegister(ScratchRSrcReg, BasePtrReg));
   }
 
   for (MCRegister Reg : MFI->WWMReservedRegs) {
     reserveRegisterTuples(Reserved, Reg);
   }
 
   // FIXME: Stop using reserved registers for this.
   for (MCPhysReg Reg : MFI->getAGPRSpillVGPRs())