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Made to work with troff

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ceriel
1990-06-20 10:05:22 +00:00
parent 955002df6c
commit d3a17633aa
25 changed files with 583 additions and 456 deletions
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doc/ego/bo/bo1
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@@ -27,20 +27,23 @@ While-loop optimization
The straightforward way to translate a while loop is to
put the test for loop termination at the beginning of the loop.
.DS
while cond loop LAB1: Test cond
body of the loop ---> Branch On False To LAB2
end loop code for body of loop
Branch To LAB1
LAB2:
while cond loop \kyLAB1: \kxTest cond
body of the loop --->\h'|\nxu'Branch On False To LAB2
end loop\h'|\nxu'code for body of loop
\h'|\nxu'Branch To LAB1
\h'|\nyu'LAB2:
Fig. 10.1 Example of Branch Optimization
.DE
If the condition fails at the Nth iteration, the following code
gets executed (dynamically):
.DS
N * conditional branch (which fails N-1 times)
N-1 * unconditional branch
N-1 * body of the loop
.TS
l l l.
N * conditional branch (which fails N-1 times)
N-1 * unconditional branch
N-1 * body of the loop
.TE
.DE
An alternative translation is:
.DS
@@ -53,9 +56,12 @@ LAB2:
.DE
This translation results in the following profile:
.DS
N * conditional branch (which succeeds N-1 times)
1 * unconditional branch
N-1 * body of the loop
.TS
l l l.
N * conditional branch (which succeeds N-1 times)
1 * unconditional branch
N-1 * body of the loop
.TE
.DE
So the second translation will be significantly faster if N >> 2.
If N=2, execution time will be slightly increased.
@@ -79,12 +85,15 @@ the basic block that comes textually next to S must stay
in that position.
So the transformation in Fig. 10.2 is illegal.
.DS
LAB1: S1 LAB1: S1
BRA LAB2 S2
... --> BEQ LAB3
LAB2: S2 ...
BEQ LAB3 S3
S3
.TS
l l l l l.
LAB1: S1 LAB1: S1
BRA LAB2 S2
... --> BEQ LAB3
LAB2: S2 ...
BEQ LAB3 S3
S3
.TE
Fig. 10.2 An illegal transformation of Branch Optimization
.DE
@@ -118,34 +127,36 @@ the last instruction of S is a conditional branch
If such a block B is found, the control flow graph is changed
as depicted in Fig. 10.3.
.DS
| |
| v
v |
|-----<------| ----->-----|
____|____ | |
| | | |-------| |
| S1 | | | v |
| Bcc | | | .... |
|--| | | | |
| --------- | | ----|---- |
| | | | | |
| .... ^ | | S2 | |
| | | | | |
| --------- | | | | |
v | | | ^ --------- |
| | S2 | | | | |
| | BRA | | | |-----<-----
| | | | | v
| --------- | | ____|____
| | | | | |
| ------>------ | | S1 |
| | | Bnn |
|-------| | | |
| | ----|----
v | |
|----<--|
|
v
.ft 5
| |
| v
v |
|-----<------| ----->-----|
____|____ | |
| | | |-------| |
| S1 | | | v |
| Bcc | | | .... |
|--| | | | |
| --------- | | ----|---- |
| | | | | |
| .... ^ | | S2 | |
| | | | | |
| --------- | | | | |
v | | | ^ --------- |
| | S2 | | | | |
| | BRA | | | |-----<-----
| | | | | v
| --------- | | ____|____
| | | | | |
| ------>------ | | S1 |
| | | Bnn |
|-------| | | |
| | ----|----
v | |
|----<--|
|
v
.ft R
Fig. 10.3 Transformation of the CFG by Branch Optimization
.DE