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We
generate a series of branching statements with the targets of the jumps
temporarily left unspecified. Use a to-be-determined label table, each entry of
which contains a list of places that need to be back-patched. The same table
can also be used to implement labels and goto’s.
There
are two possible ways to translate switch statements.
Scheme 1:
code to evaluate E
into t
goto test
L[1]: code for S[1]
goto next
...
L[k]: code for S[k]
goto next
L[d]: code for S[d]
goto next
test:
if t = V[1] goto L[1]
...
if t = V[k] goto L[k]
goto L[d]
next:
...
Scheme 2:
code to evaluate E
into t
if t <> V[1]
goto L[1]
code for S[1]
goto next
L[1]: if t <>
V[2] goto L[2]
code for S[2]
goto next
...
L[k-1]: if t <>
V[k] goto
L[k]
code for S[k]
goto next
L[k]: code for S[d]
next:
The
first scheme is simpler to implement as it creates all the necessary labels
first and then goes for test and branching.
Case
three-address-code instructions used to translate a switch statement are as
below.
case t V1 L1
case t V2
L2
...
case t Vn-1
Ln-1
case t t Ln
label next
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