ESPL1000 Three Address Code / IR

ESPL1000 uses a variant of Three-Address Code as an intermediate representation for Assembly Code Generation.

Implementation can be found in tac.c / tac.h . This web page is to document and formalize the representation.

Concepts

• TMP: temporary variable, e.g. t4. these can be identified by the number alone.
• LOCAL: local variable, residing in stack frame
• ARG: argument to the function
• LABEL: index label, e.g. "L0" or index into functions (SST)
• CONST: compile-time known constant

Table of IR Instructions

The table shows which fields of struct TAC are defined for each TAC_KIND.
It also specifies which values are allowed for these fields.

Control Flow outside the function

TAC_KIND	Example	uint32_t dest	uint32_t arg1	(int32_t) const_value	(uint32_t) label_index	enum TAC_OP op (allowed values)
TAC_CALL	t1 = call myfn	TMP	LABEL(index into SST)	-	-	-
TAC_PARAM	param t1	TMP	-	8: 8 bit param, 16: 16 bit param	-	-
TAC_SETUP_STACKFRAME	setup_stackframe 3	-	-	CONST	-	-
TAC_SETUP_SP	setup SP	-	-	-	-	-
TAC_RETURN	return t1	TMP	-	-	-	-
TAC_LABEL_FUNCTION	main:	LABEL(index into SST)	-	-	-	-

Control Flow inside a function

TAC_KIND	Example	uint32_t dest	uint32_t arg1	(int32_t) const_value	(uint32_t) label_index	enum TAC_OP op (allowed values)
TAC_GOTO	goto L1	-	-	-	LABEL	-
TAC_IF_GOTO	if t1 goto L1	-	TMP	-	LABEL	-
TAC_IF_CMP_GOTO	if t1 < t2 goto L1	TMP	TMP	-	LABEL	TAC_OP_CMP_*
TAC_LABEL_INDEXED	L3:	-	-	-	LABEL	-

Load/Store

TAC_KIND	Example	uint32_t dest	uint32_t arg1	int32_t const_value	uint32_t label_index	enum TAC_OP op (allowed values)
TAC_LOAD_LOCAL	t1 = x	TMP	LOCAL	-	-	-
TAC_LOAD_LOCAL_ADDR	t1 = address(y)	TMP	LOCAL	-	-	-
TAC_STORE_LOCAL	x = t1	LOCAL	TMP	-	-	-
TAC_LOAD_CONST_ADDR	t1 = [const]	TMP	-	CONST	-	-
TAC_STORE_CONST_ADDR	[const] = t1	-	TMP	CONST	-	-
TAC_LOAD [NEW]	t1 = [t2]	TMP	TMP	number of bytes to load (1 or 2)	-	-
TAC_STORE [NEW]	[t1] = t2	TMP	TMP	-	-	-

Other

TAC_KIND	Example	uint32_t dest	uint32_t arg1	(int32_t) const_value	(uint32_t) label_index	enum TAC_OP op (allowed values)
TAC_BINARY_OP	t1 += t2	TMP	TMP	-	-	TAC_OP_ADD, TAC_OP_SUB, TAC_OP_MUL, TAC_OP_XOR, TAC_OP_AND, TAC_OP_OR, TAC_OP_CMP_*
TAC_UNARY_OP	t1 = -t2	TMP	TMP	-	-	TAC_OP_UNARY_*
TAC_COPY	t1 = t2	TMP	TMP	-	-	-
TAC_CONST_VALUE	t1 = 4	TMP	-	CONST	-	-
TAC_NOP	nop	-	-	-	-	-
TAC_BINARY_OP_IMMEDIATE	t3 += 2, t3 |= 5	TMP	-	CONST	-	TAC_OP_ADD, TAC_OP_SUB, TAC_OP_MUL, TAC_OP_XOR, TAC_OP_OR, TAC_OP_AND TAC_OP_SHIFT_*