LLVM: llvm::InstrStage Struct Reference (original) (raw)

These values represent a non-pipelined step in the execution of an instruction. More...

These values represent a non-pipelined step in the execution of an instruction.

Cycles represents the number of discrete time slots needed to complete the stage. Units represent the choice of functional units that can be used to complete the stage. Eg. IntUnit1, IntUnit2. NextCycles indicates how many cycles should elapse from the start of this stage to the start of the next stage in the itinerary. A value of -1 indicates that the next stage should start immediately after the current one. For example:

{ 1, x, -1 } indicates that the stage occupies FU x for 1 cycle and that the next stage starts immediately after this one.

{ 2, x|y, 1 } indicates that the stage occupies either FU x or FU y for 2 consecutive cycles and that the next stage starts one cycle after this stage starts. That is, the stage requirements overlap in time.

{ 1, x, 0 } indicates that the stage occupies FU x for 1 cycle and that the next stage starts in this same cycle. This can be used to indicate that the instruction requires multiple stages at the same time.

FU reservation can be of two different kinds:

• FUs which instruction actually requires
• FUs which instruction just reserves. Reserved unit is not available for execution of other instruction. However, several instructions can reserve the same unit several times. Such two types of units reservation is used to model instruction domain change stalls, FUs using the same resource (e.g. same register file), etc.

Definition at line 59 of file MCInstrItineraries.h.