Optimize rule-matching by reordering the OutSection-Rule-Sections loop#820
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Optimize rule-matching by reordering the OutSection-Rule-Sections loop#820parth-07 wants to merge 1 commit intoqualcomm:mainfrom
parth-07 wants to merge 1 commit intoqualcomm:mainfrom
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This commit improves the performance of linker script rule-matching by
reordering the nested OutputSection-LinkerScriptRule-InputSections loop.
Currently, the nested loop is as follows:
```
for (auto O : OutSections) {
for (auto R : O.rules()) {
for (auto S : InputSections) {
// ...
}
}
}
```
This patch changes the nested loop to:
```
for (auto S : InputSections) {
for (auto O : OutSections) {
for (auto R : O.rules()) {
// ...
}
}
}
```
The new loop structure has the following benefits:
- Once an input section is matched to a rule, we waste no iterations
over it. On the contrary, in the old design, all the input sections
are always iterated over for EACH rule.
- We do a lot of computation for a section. In the old design, all the
computations are repeated for EACH rule, whereas in the new design all
the computations happen once-per-section in the outermost loop.
On a contrived test case that make good use of linker script
rule-matching, this patch results in ~15% performance improvement
for the rule-matching phase.
Signed-off-by: Parth Arora <partaror@qti.qualcomm.com>
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Contributor
|
I like this approach, and potential savings. |
| for (Section *Section : Sections) { | ||
| ELFSection *ELFSect = llvm::dyn_cast<eld::ELFSection>(Section); | ||
| // For each input section. | ||
| for (Section *Section : Sections) { |
Contributor
There was a problem hiding this comment.
Change the variable Section to Sec or something like that.
| if (In->isSpecial()) | ||
| if (In->isSpecial()) { | ||
| IsRetrySect = true; | ||
| RetrySections.insert(std::make_pair(Section, true)); |
Contributor
There was a problem hiding this comment.
we dont need this map.
| InputSectionHash = llvm::hash_combine(SectName); | ||
| } | ||
| if (Section->getOutputSection() && !IsRetrySect) { | ||
| shouldBreak = false; |
Contributor
There was a problem hiding this comment.
shouldSkipMatch instead of shouldBreak ?
quic-areg
reviewed
Feb 13, 2026
| break; | ||
| } | ||
| } | ||
| bool shouldBreak = false; |
Contributor
There was a problem hiding this comment.
Suggested change
| bool shouldBreak = false; |
This shouldBreak is currently a no-op
| } | ||
| // For all output sections. | ||
| for (auto *Out : SectionMap) { | ||
| if (ELFSect) { |
Contributor
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Suggested change
| if (ELFSect) { | |
| if (Section->getOutputSection() && !IsRetrySect) | |
| break; | |
| if (ELFSect) { |
| // RuleMatchTimes[In] += std::chrono::system_clock::now() - Start; | ||
| } // end each rule | ||
| if (shouldBreak) | ||
| break; |
| } // end each output section | ||
| // RuleMatchTimes[In] += std::chrono::system_clock::now() - Start; | ||
| } // end each rule | ||
| if (shouldBreak) |
Contributor
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Suggested change
| if (shouldBreak) |
| } | ||
|
|
||
| void ObjectBuilder::assignInputFromOutput(eld::InputFile *Obj) { | ||
| std::unordered_map<Section *, bool> RetrySections; |
Contributor
There was a problem hiding this comment.
Is this still used anymore? We write to it but do we read it anywhere?
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This commit improves the performance of linker script rule-matching by reordering the nested OutputSection-LinkerScriptRule-InputSections loop.
Currently, the nested loop is as follows:
This patch changes the nested loop to:
The new loop structure has the following benefits:
On a contrived test case that make good use of linker script rule-matching, this patch results in ~15% performance improvement for the rule-matching phase.