HL.BSTART CALL

48-bit HL. **Group:** BSTART  |  Ch 04   Block ISA — Block-structured Control Flow  |  **Length:** 48  |  **Decode:** —

Assembly Syntax

• HL.BSTART.CALL <br_label>, <rt_label>, ->ra

Encoding

Bitfield encoding diagram. MSB is on the left, LSB on the right.

Description

[48-bit HL.] Atomic fused call with independent call-target and return-target fields; transfers to the call block and writes ra. This exact aggregate is distinct from the generic bare-call form, which preserves ra and requires an adjacent SETRET or C.SETRET.

Pseudocode (informative)

P = CurrentPC();
call_target = P + (SignExtend(simm25) << 1);
ra = (P + 4) + (ZeroExtend(uimm5) << 1);
AtomicCallTransfer(call_target, ra);

Encoding Notes

• Atomic fused CALL: call_target = P + (SignExtend(simm25) << 1); ra = (P + 4) + (ZeroExtend(uimm5) << 1). Both labels are explicit and independently relocatable.

Full Catalog Forms

Assembly	Length	Decode
HL.BSTART.CALL <br_label>, <rt_label>, ->ra	48	—

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