Some threeaddress statements that will be used later: - PowerPoint PPT Presentation
Title:
Some threeaddress statements that will be used later:
Description:
Some three-address statements that will be used later: ... Param x, set a parameter for a procedure call. Call p, n call procedure p with n parameters ... – PowerPoint PPT presentation
Number of Views:38
Avg rating:3.0/5.0
Title: Some threeaddress statements that will be used later:
1
- Some three-address statements that will be used
later - Assignment statements
- With a binary operation x y op z
- With a unary operation x op y
- With no operation(copy) x y
- Branch statements
- Unconditional jump goto L
- Conditional jumps if x relop y goto L
- Statement for procedure calls
- Param x, set a parameter for a procedure call
- Call p, n call procedure p with n parameters
- Return y return from a procedure with return
value y
2
- Example instructions for procedure call p(x1,
x2, x3, , xn) - param x1
- param x2
- param xn
- call p, n
- Indexed assignments
- x yi and xi y
- Address and pointer assignments
- x y, x y
3
- Translation scheme to produce three address code
for assignment statement. - Emit (instruction) emit a three address
statement to the output - newtemp return a new temporary
- lookup(identifier) check if the identifier is in
the symbol table. - Grammar
- S-gtidE
- E-gtE1E2
- E-gtE1E2
- E-gt-E
- E-gt(E1)
- E-gtid
- E-gtnum
4
- S-gtidE plookup(id.name)
- if (p!nil) then emit(p
E.place) else error - E-gtE1E2 E.place newtemp
- emit(E.place E1.place
E2.place) - E-gtE1E2 E.place newtemp
- emit(E.place E1.place
E2.place) - E-gt-E1 E.place newtemp
- emit(E.place -
E1.place) - E-gt(E1) E.place E1.place
- E-gtid p lookup(id.name)
- if (p! nil) then E.place p
else error - E-gtnum E.place num.val
- Example x a 10 20 -30 with bottom-up
parsing.
5
- Temporary names can be reused
- The code generated by E-gtE1E2 has the general
form - Evaluate E1 into t1
- Evaluate E2 into t2
- t3 t1 t2
- All temporaries used in E1 are dead after t1 is
evaluated - All temporaries used in E2 are dead after t2 is
evaluated - T1 and t2 are dead after t3 is assigned
- Temporaries can be managed as a stack
- Keep a counter c, newtemp increases c, when a
temporary is used, decreases c. - See the previous example.
6
- Addressing array elements
- Arrays are typically stored in block of
consecutive locations. - One-dimensional arrays
- A arraylow..high of
- the ith elements is at
- base (i-low)width ? iwidth (base
lowwidth) - Multi-dimensional arrays
- Row major or column major forms
- Row major a1,1, a1,2, a1,3, a2,1,
a2,2, a2,3 - Column major a1,1, a2,1, a1, 2, a2,
2,a1, 3,a2,3 - In raw major form, the address of ai1, i2 is
- Base((i1-low1)(high2-low21)i2-low2)width
7
- In general, for any dimensional array, the
address of ai1, i2, i3, , ik can be computed
as follows - Let highj and lowj be for bounds for ij
- Let nj highj lowj 1
- The address is
- (((i1n2i2)n3)nkik)width base
((low1n2low2)n3)nklowk) width - When generating code for array references, we
need to explicitly compute the address.
8
- Translation scheme for array elements
- Limit(array, j) returns njhighj-lowj1
- .place the temporarys or variables
- .offset offset from the base, null if not an
array reference - Grammar
- S-gtL E
- E-gtEE
- E-gt(E)
- E-gtL
- L-gtElist
- L-gtid
- Elist-gtElist, E
- Elist-gtidE
9
- S-gtL E if L.offset null then emit(L.place
E.place) - else emit(L.placeL.offset
E.place) - E-gtE1E2 E.place newtemp
- emit(E.place E1.place
E2.place) - E-gt(E1) E.place E1.place
- E-gtL if L.offset null then E.place L.place
- else E.place newtemp
- emit(E.place L.place
L.offset ) - L-gtElist L.place newtemp L.offset
newtemp - emit(L.place
c(Elist.array)) - emit(L.offset Elist.place
width(Elist.array)
10
- L-gtid L.place lookup(id.name)
- L.offset null
- Elist-gtElist1, E
- t newtemp
- m Elist1.ndim 1
- emit(t Elist1.place limit(Elist1.array
, m)) - emit(t, t E.place)
- Elist.array Elist1.array
- Elist.place t
- Elist.ndim m
- Elist-gtidE Elist.array lookup(id.name)
- Elist.place E.place
- Elist.ndim 1
11
- Example A array1..10, 1..20 of integer
- Translate x Ay, z
- Accessing fields in records?
- a.b.c.d x
- X a.b.c.d
Recommended
CrystalGraphics Presentations
