This trace follows the actual state transitions behind the companion Instruction Pipelines and Dependency Hazards. It describes a common execution path; implementation details can vary, so keep the contract separate from the mechanism.
Step 1: Fetch and decode instruction
A processor pipeline overlaps stages of multiple instructions, much like an assembly line. Pipelining aims to increase instruction throughput; it does not necessarily reduce the latency of one instruction. The benefit depends on keeping stages supplied with independent work and resolving control decisions quickly.
Step 2: Check operand dependencies
If instruction B needs a value that instruction A has not produced yet, B has a data dependency. Forwarding may deliver a result directly between stages; otherwise the processor may insert a stall. A branch creates a control dependency, so the pipeline may speculate on a path and later discard work if the prediction was wrong.
Step 3: Forward a value or stall
If a consumer needs a value not yet produced, forwarding may satisfy it or the pipeline must wait; a mispredicted branch discards speculative work from the wrong path.
At this point, record the state that changed and check the invariant before advancing. If the operation repeats, make clear which values persist and which are recomputed.
Step 4: Resolve control flow
Pipeline diagrams are simplified models: real processors can issue multiple instructions, execute out of order, and retire results in program order. Dependencies constrain parallelism even when many functional units are available. A cache miss can leave dependent instructions waiting for data.
Step 5: Retire the result in order
Consider a sequence where each instruction adds the result of the previous one. Why does a wide processor not necessarily execute the whole sequence at once? What change could expose independent work?
The trace is complete when the result satisfies the stated contract. Compare this model with the concrete runtime or system you are studying before making a performance claim.