§ 4.6.4. Prediction Recovery

Recovery compares the next PC actually chosen by Execute with the prediction saved for that instruction. Comparing only taken/not-taken is insufficient: the predicted address itself may be wrong, and a taken branch to PC+4 needs no correction.

Component	Description	Structural	Behavioral
RV32IBranchRecovery	Full-address comparison and accepted-resolution qualification	Yes	Yes
RV32IPredictionPath	Predictor, saved next-PC values, recovery and PC selection	Yes	Yes

BranchRecovery

IO pins

Pin	Direction	Width	Description
VALID, PRETERMINAL	Input	1 each	Execute slot validity and early-terminal status
ADVANCE, KILL	Input	1 each	EX/MEM will capture; an older terminal/fault instead kills this slot
IS_BRANCH, RST	Input	1 each	Conditional-branch kind; reset
PREDICTED_PC, FALLTHROUGH_PC, TARGET_PC	Input	32 each	Saved prediction and the two candidate next addresses
TAKEN	Input	1	Select TARGET_PC for a taken branch or jump, otherwise FALLTHROUGH_PC
MISPREDICT	Output	1	Eligible valid instruction has unequal addresses
RESOLVE	Output	1	Eligible instruction actually leaves Execute without being killed
UPDATE	Output	1	RESOLVE and IS_BRANCH; train once at this edge
RECOVERY, BRANCH_MISS	Output	1 each	Qualified next-PC correction; conditional-branch subset

Behavior and C++ example

MISPREDICT is a request to the coordinator, so it is deliberately not gated by ADVANCE. The coordinator may hold it while an older memory request waits. RESOLVE, UPDATE and the observation pulses are gated by actual advancement and older-instruction priority. This avoids both a combinational dependency loop and repeated table training during a stall.

struct Recovery {bool mispredict,resolve,update,recovery,branch_miss;};
inline Recovery recover(bool valid,bool preterminal,bool advance,bool kill,bool branch,bool reset,
                        uint32_t predicted_pc,uint32_t fallthrough_pc,uint32_t target_pc,bool taken) {
    const bool eligible=valid&&!preterminal&&!reset;
    const bool different=taken ? predicted_pc!=target_pc : predicted_pc!=fallthrough_pc;
    const bool resolve=eligible&&advance&&!kill;
    return {eligible&&different,resolve,resolve&&branch,resolve&&different,resolve&&branch&&different};
}

Implementation

Two structural XOR/reduction networks compare the saved prediction with fallthrough and target in parallel. TAKEN selects the one-bit mismatch. Thus branch resolution does not first wait for a 32-bit next-PC mux and then a comparison. Qualification gates generate the outputs. The behavioral implementation selects the same address predicate. This component stores nothing. If target equals fallthrough, a direction difference alone causes no recovery.

Examples

The table exhausts 256 combinations of validity, terminal status, advancement, kill, instruction kind, reset, selected-address difference and taken direction, followed by two target-equals-fallthrough cases.

All 258 recorded rows of RV32IBranchRecoveryTest, in checkpoint order. Outputs are test expectations verified against the simulation. Time is the absolute settled checkpoint time in simulator units, not milliseconds or CPU cycles.

Default scenario profile: prediction-preview-preview / structural (c00b720a1b70c77a). Changing fidelity or the circuit can change these times.

Checkpointzero-based number · timeline label	Timesimulator units	ADVANCEInput · 1 bit	FALLTHROUGH_PCInput · 32 bit	IS_BRANCHInput · 1 bit	KILLInput · 1 bit	PREDICTED_PCInput · 32 bit	PRETERMINALInput · 1 bit	RSTInput · 1 bit	TAKENInput · 1 bit	TARGET_PCInput · 32 bit	VALIDInput · 1 bit	BRANCH_MISSExpected output · 1 bit	MISPREDICTExpected output · 1 bit	RECOVERYExpected output · 1 bit	RESOLVEExpected output · 1 bit	UPDATEExpected output · 1 bit
#0case-0	10	0	0x00000100	0	0	0x00000100	0	0	0	0x00000200	0	0	0	0	0	0
#1case-1	14	0	0x00000100	0	0	0x00000100	0	0	0	0x00000200	1	0	0	0	0	0
#2case-2	18	0	0x00000100	0	0	0x00000100	1	0	0	0x00000200	0	0	0	0	0	0
#3case-3	20	0	0x00000100	0	0	0x00000100	1	0	0	0x00000200	1	0	0	0	0	0
#4case-4	23	1	0x00000100	0	0	0x00000100	0	0	0	0x00000200	0	0	0	0	0	0
#5case-5	29	1	0x00000100	0	0	0x00000100	0	0	0	0x00000200	1	0	0	0	1	0
#6case-6	35	1	0x00000100	0	0	0x00000100	1	0	0	0x00000200	0	0	0	0	0	0
#7case-7	37	1	0x00000100	0	0	0x00000100	1	0	0	0x00000200	1	0	0	0	0	0
#8case-8	40	0	0x00000100	0	1	0x00000100	0	0	0	0x00000200	0	0	0	0	0	0
#9case-9	44	0	0x00000100	0	1	0x00000100	0	0	0	0x00000200	1	0	0	0	0	0
#10case-10	48	0	0x00000100	0	1	0x00000100	1	0	0	0x00000200	0	0	0	0	0	0
#11case-11	50	0	0x00000100	0	1	0x00000100	1	0	0	0x00000200	1	0	0	0	0	0
#12case-12	53	1	0x00000100	0	1	0x00000100	0	0	0	0x00000200	0	0	0	0	0	0
#13case-13	58	1	0x00000100	0	1	0x00000100	0	0	0	0x00000200	1	0	0	0	0	0
#14case-14	63	1	0x00000100	0	1	0x00000100	1	0	0	0x00000200	0	0	0	0	0	0
#15case-15	65	1	0x00000100	0	1	0x00000100	1	0	0	0x00000200	1	0	0	0	0	0
#16case-16	68	0	0x00000100	1	0	0x00000100	0	0	0	0x00000200	0	0	0	0	0	0
#17case-17	72	0	0x00000100	1	0	0x00000100	0	0	0	0x00000200	1	0	0	0	0	0
#18case-18	76	0	0x00000100	1	0	0x00000100	1	0	0	0x00000200	0	0	0	0	0	0
#19case-19	78	0	0x00000100	1	0	0x00000100	1	0	0	0x00000200	1	0	0	0	0	0
#20case-20	81	1	0x00000100	1	0	0x00000100	0	0	0	0x00000200	0	0	0	0	0	0
#21case-21	87	1	0x00000100	1	0	0x00000100	0	0	0	0x00000200	1	0	0	0	1	1
#22case-22	93	1	0x00000100	1	0	0x00000100	1	0	0	0x00000200	0	0	0	0	0	0
#23case-23	95	1	0x00000100	1	0	0x00000100	1	0	0	0x00000200	1	0	0	0	0	0
#24case-24	98	0	0x00000100	1	1	0x00000100	0	0	0	0x00000200	0	0	0	0	0	0
#25case-25	102	0	0x00000100	1	1	0x00000100	0	0	0	0x00000200	1	0	0	0	0	0
#26case-26	106	0	0x00000100	1	1	0x00000100	1	0	0	0x00000200	0	0	0	0	0	0
#27case-27	108	0	0x00000100	1	1	0x00000100	1	0	0	0x00000200	1	0	0	0	0	0
#28case-28	111	1	0x00000100	1	1	0x00000100	0	0	0	0x00000200	0	0	0	0	0	0
#29case-29	116	1	0x00000100	1	1	0x00000100	0	0	0	0x00000200	1	0	0	0	0	0
#30case-30	121	1	0x00000100	1	1	0x00000100	1	0	0	0x00000200	0	0	0	0	0	0
#31case-31	123	1	0x00000100	1	1	0x00000100	1	0	0	0x00000200	1	0	0	0	0	0
#32case-32	126	0	0x00000100	0	0	0x00000100	0	1	0	0x00000200	0	0	0	0	0	0
#33case-33	129	0	0x00000100	0	0	0x00000100	0	1	0	0x00000200	1	0	0	0	0	0
#34case-34	132	0	0x00000100	0	0	0x00000100	1	1	0	0x00000200	0	0	0	0	0	0
#35case-35	134	0	0x00000100	0	0	0x00000100	1	1	0	0x00000200	1	0	0	0	0	0
#36case-36	137	1	0x00000100	0	0	0x00000100	0	1	0	0x00000200	0	0	0	0	0	0
#37case-37	140	1	0x00000100	0	0	0x00000100	0	1	0	0x00000200	1	0	0	0	0	0
#38case-38	143	1	0x00000100	0	0	0x00000100	1	1	0	0x00000200	0	0	0	0	0	0
#39case-39	145	1	0x00000100	0	0	0x00000100	1	1	0	0x00000200	1	0	0	0	0	0
#40case-40	148	0	0x00000100	0	1	0x00000100	0	1	0	0x00000200	0	0	0	0	0	0
#41case-41	151	0	0x00000100	0	1	0x00000100	0	1	0	0x00000200	1	0	0	0	0	0
#42case-42	154	0	0x00000100	0	1	0x00000100	1	1	0	0x00000200	0	0	0	0	0	0
#43case-43	156	0	0x00000100	0	1	0x00000100	1	1	0	0x00000200	1	0	0	0	0	0
#44case-44	159	1	0x00000100	0	1	0x00000100	0	1	0	0x00000200	0	0	0	0	0	0
#45case-45	162	1	0x00000100	0	1	0x00000100	0	1	0	0x00000200	1	0	0	0	0	0
#46case-46	165	1	0x00000100	0	1	0x00000100	1	1	0	0x00000200	0	0	0	0	0	0
#47case-47	167	1	0x00000100	0	1	0x00000100	1	1	0	0x00000200	1	0	0	0	0	0
#48case-48	170	0	0x00000100	1	0	0x00000100	0	1	0	0x00000200	0	0	0	0	0	0
#49case-49	173	0	0x00000100	1	0	0x00000100	0	1	0	0x00000200	1	0	0	0	0	0
#50case-50	176	0	0x00000100	1	0	0x00000100	1	1	0	0x00000200	0	0	0	0	0	0
#51case-51	178	0	0x00000100	1	0	0x00000100	1	1	0	0x00000200	1	0	0	0	0	0
#52case-52	181	1	0x00000100	1	0	0x00000100	0	1	0	0x00000200	0	0	0	0	0	0
#53case-53	184	1	0x00000100	1	0	0x00000100	0	1	0	0x00000200	1	0	0	0	0	0
#54case-54	187	1	0x00000100	1	0	0x00000100	1	1	0	0x00000200	0	0	0	0	0	0
#55case-55	189	1	0x00000100	1	0	0x00000100	1	1	0	0x00000200	1	0	0	0	0	0
#56case-56	192	0	0x00000100	1	1	0x00000100	0	1	0	0x00000200	0	0	0	0	0	0
#57case-57	195	0	0x00000100	1	1	0x00000100	0	1	0	0x00000200	1	0	0	0	0	0
#58case-58	198	0	0x00000100	1	1	0x00000100	1	1	0	0x00000200	0	0	0	0	0	0
#59case-59	200	0	0x00000100	1	1	0x00000100	1	1	0	0x00000200	1	0	0	0	0	0
#60case-60	203	1	0x00000100	1	1	0x00000100	0	1	0	0x00000200	0	0	0	0	0	0
#61case-61	206	1	0x00000100	1	1	0x00000100	0	1	0	0x00000200	1	0	0	0	0	0
#62case-62	209	1	0x00000100	1	1	0x00000100	1	1	0	0x00000200	0	0	0	0	0	0
#63case-63	211	1	0x00000100	1	1	0x00000100	1	1	0	0x00000200	1	0	0	0	0	0
#64case-64	222	0	0x80000100	0	0	0x00000100	0	0	0	0x00000200	0	0	0	0	0	0
#65case-65	226	0	0x80000100	0	0	0x00000100	0	0	0	0x00000200	1	0	1	0	0	0
#66case-66	230	0	0x80000100	0	0	0x00000100	1	0	0	0x00000200	0	0	0	0	0	0
#67case-67	232	0	0x80000100	0	0	0x00000100	1	0	0	0x00000200	1	0	0	0	0	0
#68case-68	235	1	0x80000100	0	0	0x00000100	0	0	0	0x00000200	0	0	0	0	0	0
#69case-69	242	1	0x80000100	0	0	0x00000100	0	0	0	0x00000200	1	0	1	1	1	0
#70case-70	249	1	0x80000100	0	0	0x00000100	1	0	0	0x00000200	0	0	0	0	0	0
#71case-71	251	1	0x80000100	0	0	0x00000100	1	0	0	0x00000200	1	0	0	0	0	0
#72case-72	254	0	0x80000100	0	1	0x00000100	0	0	0	0x00000200	0	0	0	0	0	0
#73case-73	258	0	0x80000100	0	1	0x00000100	0	0	0	0x00000200	1	0	1	0	0	0
#74case-74	262	0	0x80000100	0	1	0x00000100	1	0	0	0x00000200	0	0	0	0	0	0
#75case-75	264	0	0x80000100	0	1	0x00000100	1	0	0	0x00000200	1	0	0	0	0	0
#76case-76	267	1	0x80000100	0	1	0x00000100	0	0	0	0x00000200	0	0	0	0	0	0
#77case-77	272	1	0x80000100	0	1	0x00000100	0	0	0	0x00000200	1	0	1	0	0	0
#78case-78	277	1	0x80000100	0	1	0x00000100	1	0	0	0x00000200	0	0	0	0	0	0
#79case-79	279	1	0x80000100	0	1	0x00000100	1	0	0	0x00000200	1	0	0	0	0	0
#80case-80	282	0	0x80000100	1	0	0x00000100	0	0	0	0x00000200	0	0	0	0	0	0
#81case-81	286	0	0x80000100	1	0	0x00000100	0	0	0	0x00000200	1	0	1	0	0	0
#82case-82	290	0	0x80000100	1	0	0x00000100	1	0	0	0x00000200	0	0	0	0	0	0
#83case-83	292	0	0x80000100	1	0	0x00000100	1	0	0	0x00000200	1	0	0	0	0	0
#84case-84	295	1	0x80000100	1	0	0x00000100	0	0	0	0x00000200	0	0	0	0	0	0
#85case-85	302	1	0x80000100	1	0	0x00000100	0	0	0	0x00000200	1	1	1	1	1	1
#86case-86	309	1	0x80000100	1	0	0x00000100	1	0	0	0x00000200	0	0	0	0	0	0
#87case-87	311	1	0x80000100	1	0	0x00000100	1	0	0	0x00000200	1	0	0	0	0	0
#88case-88	314	0	0x80000100	1	1	0x00000100	0	0	0	0x00000200	0	0	0	0	0	0
#89case-89	318	0	0x80000100	1	1	0x00000100	0	0	0	0x00000200	1	0	1	0	0	0
#90case-90	322	0	0x80000100	1	1	0x00000100	1	0	0	0x00000200	0	0	0	0	0	0
#91case-91	324	0	0x80000100	1	1	0x00000100	1	0	0	0x00000200	1	0	0	0	0	0
#92case-92	327	1	0x80000100	1	1	0x00000100	0	0	0	0x00000200	0	0	0	0	0	0
#93case-93	332	1	0x80000100	1	1	0x00000100	0	0	0	0x00000200	1	0	1	0	0	0
#94case-94	337	1	0x80000100	1	1	0x00000100	1	0	0	0x00000200	0	0	0	0	0	0
#95case-95	339	1	0x80000100	1	1	0x00000100	1	0	0	0x00000200	1	0	0	0	0	0
#96case-96	342	0	0x80000100	0	0	0x00000100	0	1	0	0x00000200	0	0	0	0	0	0
#97case-97	345	0	0x80000100	0	0	0x00000100	0	1	0	0x00000200	1	0	0	0	0	0
#98case-98	348	0	0x80000100	0	0	0x00000100	1	1	0	0x00000200	0	0	0	0	0	0
#99case-99	350	0	0x80000100	0	0	0x00000100	1	1	0	0x00000200	1	0	0	0	0	0
#100case-100	353	1	0x80000100	0	0	0x00000100	0	1	0	0x00000200	0	0	0	0	0	0
#101case-101	356	1	0x80000100	0	0	0x00000100	0	1	0	0x00000200	1	0	0	0	0	0
#102case-102	359	1	0x80000100	0	0	0x00000100	1	1	0	0x00000200	0	0	0	0	0	0
#103case-103	361	1	0x80000100	0	0	0x00000100	1	1	0	0x00000200	1	0	0	0	0	0
#104case-104	364	0	0x80000100	0	1	0x00000100	0	1	0	0x00000200	0	0	0	0	0	0
#105case-105	367	0	0x80000100	0	1	0x00000100	0	1	0	0x00000200	1	0	0	0	0	0
#106case-106	370	0	0x80000100	0	1	0x00000100	1	1	0	0x00000200	0	0	0	0	0	0
#107case-107	372	0	0x80000100	0	1	0x00000100	1	1	0	0x00000200	1	0	0	0	0	0
#108case-108	375	1	0x80000100	0	1	0x00000100	0	1	0	0x00000200	0	0	0	0	0	0
#109case-109	378	1	0x80000100	0	1	0x00000100	0	1	0	0x00000200	1	0	0	0	0	0
#110case-110	381	1	0x80000100	0	1	0x00000100	1	1	0	0x00000200	0	0	0	0	0	0
#111case-111	383	1	0x80000100	0	1	0x00000100	1	1	0	0x00000200	1	0	0	0	0	0
#112case-112	386	0	0x80000100	1	0	0x00000100	0	1	0	0x00000200	0	0	0	0	0	0
#113case-113	389	0	0x80000100	1	0	0x00000100	0	1	0	0x00000200	1	0	0	0	0	0
#114case-114	392	0	0x80000100	1	0	0x00000100	1	1	0	0x00000200	0	0	0	0	0	0
#115case-115	394	0	0x80000100	1	0	0x00000100	1	1	0	0x00000200	1	0	0	0	0	0
#116case-116	397	1	0x80000100	1	0	0x00000100	0	1	0	0x00000200	0	0	0	0	0	0
#117case-117	400	1	0x80000100	1	0	0x00000100	0	1	0	0x00000200	1	0	0	0	0	0
#118case-118	403	1	0x80000100	1	0	0x00000100	1	1	0	0x00000200	0	0	0	0	0	0
#119case-119	405	1	0x80000100	1	0	0x00000100	1	1	0	0x00000200	1	0	0	0	0	0
#120case-120	408	0	0x80000100	1	1	0x00000100	0	1	0	0x00000200	0	0	0	0	0	0
#121case-121	411	0	0x80000100	1	1	0x00000100	0	1	0	0x00000200	1	0	0	0	0	0
#122case-122	414	0	0x80000100	1	1	0x00000100	1	1	0	0x00000200	0	0	0	0	0	0
#123case-123	416	0	0x80000100	1	1	0x00000100	1	1	0	0x00000200	1	0	0	0	0	0
#124case-124	419	1	0x80000100	1	1	0x00000100	0	1	0	0x00000200	0	0	0	0	0	0
#125case-125	422	1	0x80000100	1	1	0x00000100	0	1	0	0x00000200	1	0	0	0	0	0
#126case-126	425	1	0x80000100	1	1	0x00000100	1	1	0	0x00000200	0	0	0	0	0	0
#127case-127	427	1	0x80000100	1	1	0x00000100	1	1	0	0x00000200	1	0	0	0	0	0
#128case-128	438	0	0x00000200	0	0	0x00000100	0	0	1	0x00000100	0	0	0	0	0	0
#129case-129	442	0	0x00000200	0	0	0x00000100	0	0	1	0x00000100	1	0	0	0	0	0
#130case-130	446	0	0x00000200	0	0	0x00000100	1	0	1	0x00000100	0	0	0	0	0	0
#131case-131	448	0	0x00000200	0	0	0x00000100	1	0	1	0x00000100	1	0	0	0	0	0
#132case-132	451	1	0x00000200	0	0	0x00000100	0	0	1	0x00000100	0	0	0	0	0	0
#133case-133	457	1	0x00000200	0	0	0x00000100	0	0	1	0x00000100	1	0	0	0	1	0
#134case-134	463	1	0x00000200	0	0	0x00000100	1	0	1	0x00000100	0	0	0	0	0	0
#135case-135	465	1	0x00000200	0	0	0x00000100	1	0	1	0x00000100	1	0	0	0	0	0
#136case-136	468	0	0x00000200	0	1	0x00000100	0	0	1	0x00000100	0	0	0	0	0	0
#137case-137	472	0	0x00000200	0	1	0x00000100	0	0	1	0x00000100	1	0	0	0	0	0
#138case-138	476	0	0x00000200	0	1	0x00000100	1	0	1	0x00000100	0	0	0	0	0	0
#139case-139	478	0	0x00000200	0	1	0x00000100	1	0	1	0x00000100	1	0	0	0	0	0
#140case-140	481	1	0x00000200	0	1	0x00000100	0	0	1	0x00000100	0	0	0	0	0	0
#141case-141	486	1	0x00000200	0	1	0x00000100	0	0	1	0x00000100	1	0	0	0	0	0
#142case-142	491	1	0x00000200	0	1	0x00000100	1	0	1	0x00000100	0	0	0	0	0	0
#143case-143	493	1	0x00000200	0	1	0x00000100	1	0	1	0x00000100	1	0	0	0	0	0
#144case-144	496	0	0x00000200	1	0	0x00000100	0	0	1	0x00000100	0	0	0	0	0	0
#145case-145	500	0	0x00000200	1	0	0x00000100	0	0	1	0x00000100	1	0	0	0	0	0
#146case-146	504	0	0x00000200	1	0	0x00000100	1	0	1	0x00000100	0	0	0	0	0	0
#147case-147	506	0	0x00000200	1	0	0x00000100	1	0	1	0x00000100	1	0	0	0	0	0
#148case-148	509	1	0x00000200	1	0	0x00000100	0	0	1	0x00000100	0	0	0	0	0	0
#149case-149	515	1	0x00000200	1	0	0x00000100	0	0	1	0x00000100	1	0	0	0	1	1
#150case-150	521	1	0x00000200	1	0	0x00000100	1	0	1	0x00000100	0	0	0	0	0	0
#151case-151	523	1	0x00000200	1	0	0x00000100	1	0	1	0x00000100	1	0	0	0	0	0
#152case-152	526	0	0x00000200	1	1	0x00000100	0	0	1	0x00000100	0	0	0	0	0	0
#153case-153	530	0	0x00000200	1	1	0x00000100	0	0	1	0x00000100	1	0	0	0	0	0
#154case-154	534	0	0x00000200	1	1	0x00000100	1	0	1	0x00000100	0	0	0	0	0	0
#155case-155	536	0	0x00000200	1	1	0x00000100	1	0	1	0x00000100	1	0	0	0	0	0
#156case-156	539	1	0x00000200	1	1	0x00000100	0	0	1	0x00000100	0	0	0	0	0	0
#157case-157	544	1	0x00000200	1	1	0x00000100	0	0	1	0x00000100	1	0	0	0	0	0
#158case-158	549	1	0x00000200	1	1	0x00000100	1	0	1	0x00000100	0	0	0	0	0	0
#159case-159	551	1	0x00000200	1	1	0x00000100	1	0	1	0x00000100	1	0	0	0	0	0
#160case-160	554	0	0x00000200	0	0	0x00000100	0	1	1	0x00000100	0	0	0	0	0	0
#161case-161	557	0	0x00000200	0	0	0x00000100	0	1	1	0x00000100	1	0	0	0	0	0
#162case-162	560	0	0x00000200	0	0	0x00000100	1	1	1	0x00000100	0	0	0	0	0	0
#163case-163	562	0	0x00000200	0	0	0x00000100	1	1	1	0x00000100	1	0	0	0	0	0
#164case-164	565	1	0x00000200	0	0	0x00000100	0	1	1	0x00000100	0	0	0	0	0	0
#165case-165	568	1	0x00000200	0	0	0x00000100	0	1	1	0x00000100	1	0	0	0	0	0
#166case-166	571	1	0x00000200	0	0	0x00000100	1	1	1	0x00000100	0	0	0	0	0	0
#167case-167	573	1	0x00000200	0	0	0x00000100	1	1	1	0x00000100	1	0	0	0	0	0
#168case-168	576	0	0x00000200	0	1	0x00000100	0	1	1	0x00000100	0	0	0	0	0	0
#169case-169	579	0	0x00000200	0	1	0x00000100	0	1	1	0x00000100	1	0	0	0	0	0
#170case-170	582	0	0x00000200	0	1	0x00000100	1	1	1	0x00000100	0	0	0	0	0	0
#171case-171	584	0	0x00000200	0	1	0x00000100	1	1	1	0x00000100	1	0	0	0	0	0
#172case-172	587	1	0x00000200	0	1	0x00000100	0	1	1	0x00000100	0	0	0	0	0	0
#173case-173	590	1	0x00000200	0	1	0x00000100	0	1	1	0x00000100	1	0	0	0	0	0
#174case-174	593	1	0x00000200	0	1	0x00000100	1	1	1	0x00000100	0	0	0	0	0	0
#175case-175	595	1	0x00000200	0	1	0x00000100	1	1	1	0x00000100	1	0	0	0	0	0
#176case-176	598	0	0x00000200	1	0	0x00000100	0	1	1	0x00000100	0	0	0	0	0	0
#177case-177	601	0	0x00000200	1	0	0x00000100	0	1	1	0x00000100	1	0	0	0	0	0
#178case-178	604	0	0x00000200	1	0	0x00000100	1	1	1	0x00000100	0	0	0	0	0	0
#179case-179	606	0	0x00000200	1	0	0x00000100	1	1	1	0x00000100	1	0	0	0	0	0
#180case-180	609	1	0x00000200	1	0	0x00000100	0	1	1	0x00000100	0	0	0	0	0	0
#181case-181	612	1	0x00000200	1	0	0x00000100	0	1	1	0x00000100	1	0	0	0	0	0
#182case-182	615	1	0x00000200	1	0	0x00000100	1	1	1	0x00000100	0	0	0	0	0	0
#183case-183	617	1	0x00000200	1	0	0x00000100	1	1	1	0x00000100	1	0	0	0	0	0
#184case-184	620	0	0x00000200	1	1	0x00000100	0	1	1	0x00000100	0	0	0	0	0	0
#185case-185	623	0	0x00000200	1	1	0x00000100	0	1	1	0x00000100	1	0	0	0	0	0
#186case-186	626	0	0x00000200	1	1	0x00000100	1	1	1	0x00000100	0	0	0	0	0	0
#187case-187	628	0	0x00000200	1	1	0x00000100	1	1	1	0x00000100	1	0	0	0	0	0
#188case-188	631	1	0x00000200	1	1	0x00000100	0	1	1	0x00000100	0	0	0	0	0	0
#189case-189	634	1	0x00000200	1	1	0x00000100	0	1	1	0x00000100	1	0	0	0	0	0
#190case-190	637	1	0x00000200	1	1	0x00000100	1	1	1	0x00000100	0	0	0	0	0	0
#191case-191	639	1	0x00000200	1	1	0x00000100	1	1	1	0x00000100	1	0	0	0	0	0
#192case-192	650	0	0x00000200	0	0	0x00000100	0	0	1	0x80000100	0	0	0	0	0	0
#193case-193	654	0	0x00000200	0	0	0x00000100	0	0	1	0x80000100	1	0	1	0	0	0
#194case-194	658	0	0x00000200	0	0	0x00000100	1	0	1	0x80000100	0	0	0	0	0	0
#195case-195	660	0	0x00000200	0	0	0x00000100	1	0	1	0x80000100	1	0	0	0	0	0
#196case-196	663	1	0x00000200	0	0	0x00000100	0	0	1	0x80000100	0	0	0	0	0	0
#197case-197	670	1	0x00000200	0	0	0x00000100	0	0	1	0x80000100	1	0	1	1	1	0
#198case-198	677	1	0x00000200	0	0	0x00000100	1	0	1	0x80000100	0	0	0	0	0	0
#199case-199	679	1	0x00000200	0	0	0x00000100	1	0	1	0x80000100	1	0	0	0	0	0
#200case-200	682	0	0x00000200	0	1	0x00000100	0	0	1	0x80000100	0	0	0	0	0	0
#201case-201	686	0	0x00000200	0	1	0x00000100	0	0	1	0x80000100	1	0	1	0	0	0
#202case-202	690	0	0x00000200	0	1	0x00000100	1	0	1	0x80000100	0	0	0	0	0	0
#203case-203	692	0	0x00000200	0	1	0x00000100	1	0	1	0x80000100	1	0	0	0	0	0
#204case-204	695	1	0x00000200	0	1	0x00000100	0	0	1	0x80000100	0	0	0	0	0	0
#205case-205	700	1	0x00000200	0	1	0x00000100	0	0	1	0x80000100	1	0	1	0	0	0
#206case-206	705	1	0x00000200	0	1	0x00000100	1	0	1	0x80000100	0	0	0	0	0	0
#207case-207	707	1	0x00000200	0	1	0x00000100	1	0	1	0x80000100	1	0	0	0	0	0
#208case-208	710	0	0x00000200	1	0	0x00000100	0	0	1	0x80000100	0	0	0	0	0	0
#209case-209	714	0	0x00000200	1	0	0x00000100	0	0	1	0x80000100	1	0	1	0	0	0
#210case-210	718	0	0x00000200	1	0	0x00000100	1	0	1	0x80000100	0	0	0	0	0	0
#211case-211	720	0	0x00000200	1	0	0x00000100	1	0	1	0x80000100	1	0	0	0	0	0
#212case-212	723	1	0x00000200	1	0	0x00000100	0	0	1	0x80000100	0	0	0	0	0	0
#213case-213	730	1	0x00000200	1	0	0x00000100	0	0	1	0x80000100	1	1	1	1	1	1
#214case-214	737	1	0x00000200	1	0	0x00000100	1	0	1	0x80000100	0	0	0	0	0	0
#215case-215	739	1	0x00000200	1	0	0x00000100	1	0	1	0x80000100	1	0	0	0	0	0
#216case-216	742	0	0x00000200	1	1	0x00000100	0	0	1	0x80000100	0	0	0	0	0	0
#217case-217	746	0	0x00000200	1	1	0x00000100	0	0	1	0x80000100	1	0	1	0	0	0
#218case-218	750	0	0x00000200	1	1	0x00000100	1	0	1	0x80000100	0	0	0	0	0	0
#219case-219	752	0	0x00000200	1	1	0x00000100	1	0	1	0x80000100	1	0	0	0	0	0
#220case-220	755	1	0x00000200	1	1	0x00000100	0	0	1	0x80000100	0	0	0	0	0	0
#221case-221	760	1	0x00000200	1	1	0x00000100	0	0	1	0x80000100	1	0	1	0	0	0
#222case-222	765	1	0x00000200	1	1	0x00000100	1	0	1	0x80000100	0	0	0	0	0	0
#223case-223	767	1	0x00000200	1	1	0x00000100	1	0	1	0x80000100	1	0	0	0	0	0
#224case-224	770	0	0x00000200	0	0	0x00000100	0	1	1	0x80000100	0	0	0	0	0	0
#225case-225	773	0	0x00000200	0	0	0x00000100	0	1	1	0x80000100	1	0	0	0	0	0
#226case-226	776	0	0x00000200	0	0	0x00000100	1	1	1	0x80000100	0	0	0	0	0	0
#227case-227	778	0	0x00000200	0	0	0x00000100	1	1	1	0x80000100	1	0	0	0	0	0
#228case-228	781	1	0x00000200	0	0	0x00000100	0	1	1	0x80000100	0	0	0	0	0	0
#229case-229	784	1	0x00000200	0	0	0x00000100	0	1	1	0x80000100	1	0	0	0	0	0
#230case-230	787	1	0x00000200	0	0	0x00000100	1	1	1	0x80000100	0	0	0	0	0	0
#231case-231	789	1	0x00000200	0	0	0x00000100	1	1	1	0x80000100	1	0	0	0	0	0
#232case-232	792	0	0x00000200	0	1	0x00000100	0	1	1	0x80000100	0	0	0	0	0	0
#233case-233	795	0	0x00000200	0	1	0x00000100	0	1	1	0x80000100	1	0	0	0	0	0
#234case-234	798	0	0x00000200	0	1	0x00000100	1	1	1	0x80000100	0	0	0	0	0	0
#235case-235	800	0	0x00000200	0	1	0x00000100	1	1	1	0x80000100	1	0	0	0	0	0
#236case-236	803	1	0x00000200	0	1	0x00000100	0	1	1	0x80000100	0	0	0	0	0	0
#237case-237	806	1	0x00000200	0	1	0x00000100	0	1	1	0x80000100	1	0	0	0	0	0
#238case-238	809	1	0x00000200	0	1	0x00000100	1	1	1	0x80000100	0	0	0	0	0	0
#239case-239	811	1	0x00000200	0	1	0x00000100	1	1	1	0x80000100	1	0	0	0	0	0
#240case-240	814	0	0x00000200	1	0	0x00000100	0	1	1	0x80000100	0	0	0	0	0	0
#241case-241	817	0	0x00000200	1	0	0x00000100	0	1	1	0x80000100	1	0	0	0	0	0
#242case-242	820	0	0x00000200	1	0	0x00000100	1	1	1	0x80000100	0	0	0	0	0	0
#243case-243	822	0	0x00000200	1	0	0x00000100	1	1	1	0x80000100	1	0	0	0	0	0
#244case-244	825	1	0x00000200	1	0	0x00000100	0	1	1	0x80000100	0	0	0	0	0	0
#245case-245	828	1	0x00000200	1	0	0x00000100	0	1	1	0x80000100	1	0	0	0	0	0
#246case-246	831	1	0x00000200	1	0	0x00000100	1	1	1	0x80000100	0	0	0	0	0	0
#247case-247	833	1	0x00000200	1	0	0x00000100	1	1	1	0x80000100	1	0	0	0	0	0
#248case-248	836	0	0x00000200	1	1	0x00000100	0	1	1	0x80000100	0	0	0	0	0	0
#249case-249	839	0	0x00000200	1	1	0x00000100	0	1	1	0x80000100	1	0	0	0	0	0
#250case-250	842	0	0x00000200	1	1	0x00000100	1	1	1	0x80000100	0	0	0	0	0	0
#251case-251	844	0	0x00000200	1	1	0x00000100	1	1	1	0x80000100	1	0	0	0	0	0
#252case-252	847	1	0x00000200	1	1	0x00000100	0	1	1	0x80000100	0	0	0	0	0	0
#253case-253	850	1	0x00000200	1	1	0x00000100	0	1	1	0x80000100	1	0	0	0	0	0
#254case-254	853	1	0x00000200	1	1	0x00000100	1	1	1	0x80000100	0	0	0	0	0	0
#255case-255	855	1	0x00000200	1	1	0x00000100	1	1	1	0x80000100	1	0	0	0	0	0
#256same-address-fallthrough	867	1	0x00000004	1	0	0x00000004	0	0	0	0x00000004	1	not checked	0	0	not checked	1
#257same-address-taken	870	1	0x00000004	1	0	0x00000004	0	0	1	0x00000004	1	not checked	0	0	not checked	1

Scroll within the table for all rows and pins. Buses use hexadecimal; values containing X/Z use MSB-first binary. Inputs show the declared values in effect at each checkpoint, including retained inputs. Sequential tests also replay preparation changes between checkpoints, such as lowering the clock. Use the matching checkpoint label in the simulation below.

PredictionPath

IO pins

Pin	Direction	Width	Description
CLK, RST, IF_ID_WRITE, ID_EX_WRITE	Input	1 each	Clock/reset and the actual packet-register enables
FETCH_PC, FETCH_INSTRUCTION	Input	32 each	Current accepted-candidate fetch
EX_PC, EX_FALLTHROUGH_PC, EX_TARGET_PC	Input	32 each	Execute instruction identity and candidate next addresses
EX_CONTROL_TAKEN	Input	1	Taken conditional branch or jump; selects the actual candidate
EX_VALID, EX_PRETERMINAL, EX_ADVANCE, EX_KILL	Input	1 each	Recovery qualifications from packet and coordinator
EX_IS_BRANCH, EX_TAKEN	Input	1 each	Actual conditional-branch kind and outcome
REDIRECT_APPLY	Input	1	Coordinator permits correction of Fetch PC
PREDICTED_NEXT_PC, EX_PREDICTED_NEXT_PC	Output	32 each	Current lookup and saved Execute-slot prediction
FETCH_NEXT_PC	Output	32	Corrected address when REDIRECT_APPLY, otherwise current prediction
MISPREDICT, RESOLVE, UPDATE, RECOVERY, BRANCH_MISS	Output	1 each	BranchRecovery outputs

Behavior and C++ example

The same prediction and prediction_entries configuration applies as for BranchPredictor. Two Register<32> components accompany IF/ID and ID/EX; each captures using its packet's write enable. All captures use pre-edge values. A hold preserves both packet and prediction. A bubble may carry stale metadata because its real VALID bit prevents use; separate prediction-valid registers are unnecessary.

struct PredictionPath {
    Predictor predictor;
    uint32_t if_id_prediction=0,id_ex_prediction=0;
    bool previous_clock=false;
    PredictionPath(Policy p,size_t entries):predictor(p,entries) {}
    void evaluate(bool clk,bool reset,bool if_id_write,bool id_ex_write,
                  uint32_t fetch_pc,uint32_t instruction,bool ex_valid,bool preterminal,
                  bool advance,bool kill,bool branch,uint32_t ex_pc,bool taken) {
        // Compute captures BEFORE changing the table or either packet register.
        const auto lookup=predictor.lookup(fetch_pc,predecode(fetch_pc,instruction)).next_pc;
        const auto old_if_id=if_id_prediction;
        if(reset) if_id_prediction=id_ex_prediction=0;
        else if(!previous_clock&&clk) {
            if(if_id_write) if_id_prediction=lookup;
            if(id_ex_write) id_ex_prediction=old_if_id;
        }
        predictor.evaluate(clk,reset,ex_valid&&!preterminal&&advance&&!kill&&branch,ex_pc,taken);
        previous_clock=clk;
    }
    // After settling: PREDICTED_NEXT_PC = predictor.lookup(...).next_pc;
    // EX_PREDICTED_NEXT_PC = id_ex_prediction;
    // actual_pc = EX_CONTROL_TAKEN ? EX_TARGET_PC : EX_FALLTHROUGH_PC;
    // FETCH_NEXT_PC = REDIRECT_APPLY ? actual_pc : PREDICTED_NEXT_PC;
    // Other outputs = recover(..., id_ex_prediction, EX_FALLTHROUGH_PC, EX_TARGET_PC, EX_CONTROL_TAKEN).
};

Implementation

The structural children are PREDECODE, PREDICTOR, IF_ID_PREDICTION, ID_EX_PREDICTION, RECOVERY, ACTUAL_NEXT_PC, and RECOVERY_PC_SELECT. The address mux supplies correction data but is not ahead of the mismatch comparison. The compact implementation stores only the same table and two metadata words. It has no architectural register file or instruction history.

Example: correction while a load waits

Suppose an older load is in MEM and a branch is in EX. The branch resolves to a different next PC, but the load's response is not ready:

State	MISPREDICT	EX_ADVANCE	UPDATE	Effect
Data response pending	1	0	0	Hold packets and prediction; do not redirect or retrain
Successful response arrives	1	1	1 for a conditional branch	Advance older work, correct Fetch, flush younger IF/ID and ID/EX
Response is a load fault	May be 1	1 with EX_KILL=1	0	Older fault wins; branch cannot advance as valid work or train

Wrong-path instructions never reach an enabled architectural write. A killed instruction-memory request is drained rather than confused with the redirected fetch; that ownership belongs to the requester in 4.6.5.

Examples

All 8 recorded rows of RV32IPredictionPathTest, in checkpoint order. Outputs are test expectations verified against the simulation. Time is the absolute settled checkpoint time in simulator units, not milliseconds or CPU cycles.

Default scenario profile: prediction-preview-preview / structural (c00b720a1b70c77a). Changing fidelity or the circuit can change these times.

Checkpointzero-based number · timeline label	Timesimulator units	CLKInput · 1 bit	EX_ADVANCEInput · 1 bit	EX_CONTROL_TAKENInput · 1 bit	EX_FALLTHROUGH_PCInput · 32 bit	EX_IS_BRANCHInput · 1 bit	EX_KILLInput · 1 bit	EX_PCInput · 32 bit	EX_PRETERMINALInput · 1 bit	EX_TAKENInput · 1 bit	EX_TARGET_PCInput · 32 bit	EX_VALIDInput · 1 bit	FETCH_INSTRUCTIONInput · 32 bit	FETCH_PCInput · 32 bit	ID_EX_WRITEInput · 1 bit	IF_ID_WRITEInput · 1 bit	REDIRECT_APPLYInput · 1 bit	RSTInput · 1 bit	BRANCH_MISSExpected output · 1 bit	EX_PREDICTED_NEXT_PCExpected output · 32 bit	FETCH_NEXT_PCExpected output · 32 bit	MISPREDICTExpected output · 1 bit	PREDICTED_NEXT_PCExpected output · 32 bit	RECOVERYExpected output · 1 bit	RESOLVEExpected output · 1 bit	UPDATEExpected output · 1 bit
#0reset	25	0	0	0	0x00000000	0	0	0x00000000	0	0	0x00000000	0	0x00208463	0x00000000	0	0	0	1	not checked	0x00000000	0x00000008	0	0x00000008	not checked	not checked	0
#1capture-if-id	33	1	0	0	0x00000000	0	0	0x00000000	0	0	0x00000000	0	0x00208463	0x00000000	1	1	0	0	not checked	0x00000000	not checked	not checked	not checked	not checked	not checked	not checked
#2capture-id-ex	80	1	0	0	0x00000000	0	0	0x00000000	0	0	0x00000000	0	0xFE208EE3	0x00000004	1	1	0	0	not checked	0x00000008	not checked	not checked	0x00000000	not checked	not checked	not checked
#3wait-holds-update	86	0	0	0	0x00000004	1	0	0x00000000	0	0	0x00000000	1	0xFE208EE3	0x00000004	0	0	0	0	not checked	not checked	not checked	1	not checked	not checked	0	0
#4held-clock	91	1	0	0	0x00000004	1	0	0x00000000	0	0	0x00000000	1	0xFE208EE3	0x00000004	0	0	0	0	not checked	0x00000008	not checked	not checked	not checked	not checked	not checked	not checked
#5apply-correction	96	0	1	0	0x00000004	1	0	0x00000000	0	0	0x00000000	1	0xFE208EE3	0x00000004	0	0	1	0	not checked	not checked	0x00000004	not checked	not checked	not checked	not checked	1
#6older-fault-kills-training	101	0	1	0	0x00000004	1	1	0x00000000	0	0	0x00000000	1	0xFE208EE3	0x00000004	0	0	1	0	not checked	not checked	not checked	not checked	not checked	not checked	0	0
#7bubble-does-not-resolve	106	0	1	0	0x00000004	1	1	0x00000000	0	0	0x00000000	0	0xFE208EE3	0x00000004	0	0	1	0	not checked	not checked	not checked	0	not checked	not checked	not checked	not checked

Scroll within the table for all rows and pins. Buses use hexadecimal; values containing X/Z use MSB-first binary. Inputs show the declared values in effect at each checkpoint, including retained inputs. Sequential tests also replay preparation changes between checkpoints, such as lowering the clock. Use the matching checkpoint label in the simulation below.

Tests

RV32IBranchRecoveryTest checks all qualification combinations. RV32IPredictionPathTest checks metadata alignment, holds, correction, killed training and lookup/update collision ordering in both fidelities. Program tests exercise conditional branches, direct jumps and register-indirect jumps. RV32IMemoryMigrationTest combines prediction with delayed ROM/SRAM endpoints, pause/resume, wrong-path store suppression and loops.