Adds IR level PGO Instrumentation options #1992

chiragramani · 2025-09-17T00:10:22Z

This PR introduces two new instrumentation flags and plumbs them through to IRGen:

-ir-profile-generate - enable IR-level instrumentation.
-cs-profile-generate - enable context-sensitive IR-level instrumentation.

Context: https://forums.swift.org/t/ir-level-pgo-instrumentation-in-swift/82123

Open Questions (Reviewer Input Requested)

Naming:
Is -ir-profile-generate a good flag name?
-cs-profile-generate pairs nicely with Clang’s -fcs-profile-generate. However, -ir-profile-generate feels closer to Clang's -fprofile-generate but -profile-generate already exists in Swift as a frontend level and not IR level. Should it stay as is, or is there a clearer alternative?
PR separation strategy:
I also updated the auto-generated Options.swift file in this PR, I am aware its not supposed to manually updated and I have a Swift-side PR open here: Add IRPGO and CSIRPGO options to Swift swift#84335
.
Should I first land a separate PR in Swift adding only the new options, and then follow up with this PR for the Driver + IRGen functionality? My current assumption is that splitting them would help unblock this PR. Is that correct?

ellishg

Do you plan to add support for -ir-profile-use and -cs-profile-use?

ellishg · 2025-09-17T00:58:47Z

Sources/SwiftDriver/Jobs/DarwinToolchain+LinkerSupport.swift

-    if parsedOptions.hasArgument(.profileGenerate) {
-      commandLine.appendFlag("-fprofile-generate")
-    }


This feels like a bug to me. As I understand, Swift's -profile-generate flag does front-end instrumentation, and is different from Clang's -fprofile-generate.

this behavior is existing in swift-driver today, and I’m a bit wary of changing it here because there may be tests and downstream flows that rely on it. This PR is primarily adding the new pieces, that said, if you feel it’s worth addressing this legacy behavior in the same PR, please let me know and I can look into it.

Sources/SwiftOptions/Options.swift

artemcm · 2025-09-17T17:42:08Z

Just a friendly heads-up that new changes need to be added with this process:
https://github.com/swiftlang/swift-driver?tab=readme-ov-file#rebuilding-optionsswift

chiragramani · 2025-09-18T19:01:35Z

Do you plan to add support for -ir-profile-use and -cs-profile-use?

Yes, I’ve added -ir-profile-use in the Swift repo, which, in line with Clang, configures PGOOptions correctly. This PR isn’t fully up to date yet, but once the Swift PR lands, I’ll make sure to update this one as well.

chiragramani · 2025-09-18T19:03:15Z

Just a friendly heads-up that new changes need to be added with this process: https://github.com/swiftlang/swift-driver?tab=readme-ov-file#rebuilding-optionsswift

Thank you for the heads-up! I’ll take a look and make sure to follow that process.

This PR introduces three new instrumentation flags and plumbs them through to IRGen: 1. `-ir-profile-generate` - enable IR-level instrumentation. 2. `-cs-profile-generate` - enable context-sensitive IR-level instrumentation. 3. `-ir-profile-use` - IR-level PGO input profdata file to enable profile-guided optimization (both IRPGO and CSIRPGO) **Context:** https://forums.swift.org/t/ir-level-pgo-instrumentation-in-swift/82123 **Swift-driver PR:** swiftlang/swift-driver#1992 **Tests and validation:** This PR includes ir level verification tests, also checks few edge-cases when `-ir-profile-use` supplied profile is either missing or is an invalid IR profile. However, for argument validation, linking, and generating IR profiles that can later be consumed by -cs-profile-generate, I’ll need corresponding swift-driver changes. Those changes are being tracked in swiftlang/swift-driver#1992

chiragramani · 2025-10-23T19:25:03Z

Just a friendly heads-up that new changes need to be added with this process: https://github.com/swiftlang/swift-driver?tab=readme-ov-file#rebuilding-optionsswift

Thank you for the heads-up! I’ll take a look and make sure to follow that process.

Hey @artemcm , I have updated the PR post following https://github.com/swiftlang/swift-driver?tab=readme-ov-file#rebuilding-optionsswift. Please let me know if you have any other suggestions.

This PR introduces three new instrumentation flags and plumbs them through to IRGen: 1. `-ir-profile-generate` - enable IR-level instrumentation. 2. `-cs-profile-generate` - enable context-sensitive IR-level instrumentation. 3. `-ir-profile-use` - IR-level PGO input profdata file to enable profile-guided optimization (both IRPGO and CSIRPGO) **Context:** https://forums.swift.org/t/ir-level-pgo-instrumentation-in-swift/82123 **Swift-driver PR:** swiftlang/swift-driver#1992 **Tests and validation:** This PR includes ir level verification tests, also checks few edge-cases when `-ir-profile-use` supplied profile is either missing or is an invalid IR profile. However, for argument validation, linking, and generating IR profiles that can later be consumed by -cs-profile-generate, I’ll need corresponding swift-driver changes. Those changes are being tracked in swiftlang/swift-driver#1992

chiragramani · 2025-10-31T18:36:15Z

Hey @artemcm / @cachemeifyoucan , when you get a moment, could you take a look at this PR please? Thanks!

chiragramani · 2025-11-10T19:30:36Z

Hi @artemcm / @cachemeifyoucan, would you be able to review this or loop in the appropriate POC? Appreciate it!

cachemeifyoucan · 2025-11-10T21:30:02Z

Sources/SwiftDriver/Jobs/FrontendJobHelpers.swift

    try commandLine.appendLast(.profileGenerate, from: &parsedOptions)
+    try commandLine.appendLast(.irProfileGenerate, from: &parsedOptions)
+    try commandLine.appendLast(.irProfileGenerateEQ, from: &parsedOptions)
+    try commandLine.appendLast(.irProfileUse, from: &parsedOptions)


This is a flag that points to the file. It needs path remapping if needed. Use addPathOption.

Also means this is not handled correctly in swift-frontend/scanner. See the comment I added to the other review.

Thanks @cachemeifyoucan for looking into it. Are you suggesting something as follows

if let irProfileUsePath = parsedOptions.getLastArgument(.irProfileUse)?.asMultiple.last { try addPathOption(option: .irProfileUse, path: VirtualPath(path: irProfileUsePath), to: &commandLine, remap: jobNeedPathRemap) }

On trying the above, I get a fatalError in CommandLineArguments.appendFlag function

fatalError("Option cannot be appended as a flag: \(option)")

I think the option .irProfileUse is of .commaJoined similar to existing flag: profileUse and would also have the same issue, do you any suggestions on how to go about it?

drodriguez · 2025-11-10T20:43:18Z

Sources/SwiftDriver/Driver/Driver.swift

+    for i in 1..<providedGen.count {
+      let error = Error.conflictingOptions(providedGen[i - 1], providedGen[i])
+      diagnosticEngine.emit(.error(error), location: nil)
+    }


Minor: any reason for this not being similar to the C++ driver?

for i in 0..<(providedGen.count - 1) { for j in (i + 1)..<providedGen.count { let error = Error.conflictingOptions(providedGen[i], providedGen[j]) diagnosticEngine.emit(.error(error), location: nil) } }

Edit: I did not realize that you were might have been moving around existing code. @kavon might be able to answer this better, but maybe what might have worked for them and only 3 flags might not work as well for 5 flags (and when the flags do not mix gen and use like in their case).

Right, for more options, a minor code change was needed. Please let me know if you have any related suggestions.

drodriguez · 2025-11-10T21:54:18Z

Sources/SwiftDriver/Driver/Driver.swift

+      for i in 0..<(providedUse.count - 1) {
+        for j in (i + 1)..<providedUse.count {


Thinking that maybe is easier to understand (and to repeat here and above), if one uses enumerated():

for (i, left) in providedUse.enumerated() { for (j, right) in providedUse.enumerated() { guard i < j else { continue } diagnosticEngine.emit(.error(Error.conflictingOptions(left, right)), location: nil) } }

Thank you @drodriguez , I agree - the above certainly looks better. Updated!

Update Options.swift Update as per suggestions

chiragramani changed the title ~~Add ir and cs instrumentation options~~ Adds IR level PGO Instrumentation options Sep 17, 2025

chiragramani mentioned this pull request Sep 17, 2025

Add IRPGO and CSIRPGO options to Swift swiftlang/swift#84335

Merged

ellishg reviewed Sep 17, 2025

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chiragramani marked this pull request as ready for review October 20, 2025 17:34

chiragramani force-pushed the instr_options branch 2 times, most recently from df3add1 to 4edf9dd Compare October 23, 2025 19:23

cachemeifyoucan reviewed Nov 10, 2025

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drodriguez reviewed Nov 10, 2025

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chiragramani force-pushed the instr_options branch from 4edf9dd to 5f5e3dc Compare November 14, 2025 23:51

Add ir and cs instrumentation options

5839e6c

Update Options.swift Update as per suggestions

chiragramani force-pushed the instr_options branch from 5f5e3dc to 5839e6c Compare November 14, 2025 23:56

		for i in 0..<(providedUse.count - 1) {
		for j in (i + 1)..<providedUse.count {

Adds IR level PGO Instrumentation options #1992

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Adds IR level PGO Instrumentation options #1992

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chiragramani commented Sep 17, 2025 •

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