AMDGPU: Fix treating unknown mem operands as uniform (#168980)

The test changes are mostly GlobalISel specific regressions.
GlobalISel is still relying on isUniformMMO, but it doesn't really
have an excuse for doing so. These should be avoidable with new
regbankselect.

There is an additional regression for addrspacecast for cov4. We
probably ought to be using a separate PseudoSourceValue for the
access of the queue pointer.

Author: arsenm

llvm/lib/Target/AMDGPU/AMDGPUISelDAGToDAG.cpp

@@ -4451,16 +4451,14 @@ bool AMDGPUDAGToDAGISel::isUniformLoad(const SDNode *N) const {
   const auto *Ld = cast<LoadSDNode>(N);
   const MachineMemOperand *MMO = Ld->getMemOperand();
 
-  if (Ld->isDivergent()) {
-    // FIXME: We ought to able able to take the direct isDivergent result. We
-    // cannot rely on the MMO for a uniformity check, and should stop using
-    // it. This is a hack for 2 ways that the IR divergence analysis is superior
-    // to the DAG divergence: Recognizing shift-of-workitem-id as always
-    // uniform, and isSingleLaneExecution. These should be handled in the DAG
-    // version, and then this can be dropped.
-    if (!MMO->getValue() || !AMDGPU::isUniformMMO(MMO))
-      return false;
-  }
+  // FIXME: We ought to able able to take the direct isDivergent result. We
+  // cannot rely on the MMO for a uniformity check, and should stop using
+  // it. This is a hack for 2 ways that the IR divergence analysis is superior
+  // to the DAG divergence: Recognizing shift-of-workitem-id as always
+  // uniform, and isSingleLaneExecution. These should be handled in the DAG
+  // version, and then this can be dropped.
+  if (Ld->isDivergent() && !AMDGPU::isUniformMMO(MMO))
+    return false;
 
   return MMO->getSize().hasValue() &&
          Ld->getAlign() >=

llvm/lib/Target/AMDGPU/AMDGPUInstrInfo.cpp

@@ -35,15 +35,13 @@ bool AMDGPU::isUniformMMO(const MachineMemOperand *MMO) {
              PSV->isJumpTable();
     }
 
-    // FIXME: null value is should be treated as unknown, not as uniform.
-    return true;
+    // Unknown value.
+    return false;
   }
 
   // UndefValue means this is a load of a kernel input.  These are uniform.
   // Sometimes LDS instructions have constant pointers.
-  // If Ptr is null, then that means this mem operand contains a
-  // PseudoSourceValue like GOT.
-  if (!Ptr || isa<UndefValue, Constant, GlobalValue>(Ptr))
+  if (isa<UndefValue, Constant, GlobalValue>(Ptr))
     return true;
 
   if (MMO->getAddrSpace() == AMDGPUAS::CONSTANT_ADDRESS_32BIT)

llvm/lib/Target/AMDGPU/AMDGPULegalizerInfo.cpp

@@ -2362,7 +2362,7 @@ Register AMDGPULegalizerInfo::getSegmentAperture(
   if (!loadInputValue(QueuePtr, B, AMDGPUFunctionArgInfo::QUEUE_PTR))
     return Register();
 
-  // TODO: can we be smarter about machine pointer info?
+  // TODO: Use custom PseudoSourceValue
   MachinePointerInfo PtrInfo(AMDGPUAS::CONSTANT_ADDRESS);
 
   // Offset into amd_queue_t for group_segment_aperture_base_hi /