nv50_ir_ra: Remove an assign to lval->compMask

This code previously stored two rather different masks in compMask:
 1. from merge/splits (calculated in makeCompound), and
 2. in the join root for whatever register was assigned

Since we were already calculating the second type as intfMask where it
is used in checkInterference(), change that function to unconditionally
use intfMask and only use compMask for the first type.

This is functionally equavalent and keeps the types of masks separate.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24541>

src/gallium/drivers/nouveau/codegen/nv50_ir_ra.cpp

@@ -1303,7 +1303,7 @@ GCRA::checkInterference(const RIG_Node *node, Graph::EdgeIterator& ei)
    LValue *vA = node->getValue();
    LValue *vB = intf->getValue();
 
-   const uint8_t intfMask = ((1 << intf->colors) - 1) << (intf->reg & 7);
+   const uint8_t intfMask = intf->getCompMask();
 
    if (vA->compound | vB->compound) {
       // NOTE: this only works for >aligned< register tuples !
@@ -1320,11 +1320,9 @@ GCRA::checkInterference(const RIG_Node *node, Graph::EdgeIterator& ei)
 
          uint8_t mask = vD->compound ? vD->compMask : ~0;
          if (vd->compound) {
-            assert(vB->compound);
-            mask &= vd->compMask & vB->compMask;
-         } else {
-            mask &= intfMask;
+            mask &= vd->compMask;
          }
+         mask &= intfMask;
 
          INFO_DBG(prog->dbgFlags, REG_ALLOC,
                   "(%%%i)%02x X (%%%i)%02x & %02x: $r%i.%02x\n",
@@ -1383,7 +1381,6 @@ GCRA::selectRegisters()
       bool ret = regs.assign(node->reg, node->f, node->colors, node->maxReg);
       if (ret) {
          INFO_DBG(prog->dbgFlags, REG_ALLOC, "assigned reg %i\n", node->reg);
-         lval->compMask = node->getCompMask();
       } else {
          INFO_DBG(prog->dbgFlags, REG_ALLOC, "must spill: %%%i (size %u)\n",
                   lval->id, lval->reg.size);