M. Mateen Yaqoob
The University of Lahore
Spring 2014
EXAMPLE: Show how can the following operation be
performed using:
a- three address instruction
b- two address instruction
c- one address instruction
d- zero address instruction
X = (A + B) * (C + D)
 ADD R1, A, B
 R1  M[A] + M[B]
 ADD R2, C, D
 R2  M[C] + M[D]
 MUL X, R1, R2
 M[X]  R1 * R2
 MOV R1, A
 R1  M[A]
 ADD R1, B
 R1  R1 + M[B]
 MOV R2, C
 R2  M[C]
 ADD R2, D
 R2  R2 + M[D]
 MOV X, R2
 M[X] R2
 MUL X, R1
 M[X]
 R1 * M[X]
 LOAD A
 AC M[A]
 ADD B
 AC  AC + M[B]
 STORE T
 M[T ] AC
 LOAD C
 AC  M[C]
 ADD D
 AC  AC + M[D]
 MUL T
 AC  AC * M[T ]
 STORE X
 M[X]  AC Store
 Push value
 Else If operator is encountered: Pop, pop, operation, push
 Pop operand pop another operand then perform an
operation and push the result back into the stack.
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PUSH A
TOS  A Push
PUSH B
TOS  B
ADD
TOS  (A+B)
PUSH C
TOS  C
PUSH D
TOS  D
ADD
TOS  (C+D)
MUL
TOS  (C+D)*(A+B)
POP X
M[X]  TOS
(*TOS stands for top of stack).
Pop, pop, operation, push
 The family concept
 IBM System/360 1964
 DEC PDP-8
 Separates architecture from implementation
 Microporgrammed control unit
 Idea by Wilkes 1951
 Produced by IBM S/360 1964
 Cache memory
 IBM S/360 model 85 1969
 Solid State RAM
 (See memory notes)
 Microprocessors
 Intel 4004 1971
 Pipelining
 Introduces parallelism into fetch execute cycle
 Multiple processors
 Reduced Instruction Set Computer
 Key features
 Large number of general purpose registers
 or use of compiler technology to optimize register use
 Limited and simple instruction set
 Emphasis on optimising the instruction pipeline
 Software costs far exceed hardware costs
 Increasingly complex high level languages
 Semantic gap
 Leads to:
 Large instruction sets
 More addressing modes
 Hardware implementations of HLL statements
 e.g. CASE (switch) on VAX
 Ease compiler writing
 Improve execution efficiency
 Complex operations in microcode
 Support more complex HLLs
 Operations performed
 Operands used
 Execution sequencing
 Studies have been done based on programs written in HLLs
 Dynamic studies are measured during the execution of the program
 Assignments
 Movement of data
 Conditional statements (IF, LOOP)
 Sequence control
 Procedure call-return is very time consuming
 Some HLL instruction lead to many machine code operations
 Mainly local scalar variables
 Optimisation should concentrate on accessing local variables
 Very time consuming
 Depends on number of parameters passed
 Depends on level of nesting
 Most programs do not do a lot of calls followed by lots of returns
 Most variables are local
 (c.f. locality of reference)
 Best support is given by optimising most used and most time consuming features
 Large number of registers
 Operand referencing
 Careful design of pipelines
 Branch prediction etc.
 Simplified (reduced) instruction set