AMDGPU: Fix treating unknown mem operands as uniform

llvm/lib/Target/AMDGPU/AMDGPUISelDAGToDAG.cpp

@@ -4422,16 +4422,14 @@ 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

@@ -2363,7 +2363,7 @@ 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 /