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[PR #9092] [MERGED] Work around a (likely) optimizer issue with SetPixelShaderPath #27413

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opened 2026-01-31 09:21:49 +00:00 by claunia · 0 comments
claunia commented 2026-01-31 09:21:49 +00:00
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📋 Pull Request Information

Original PR: https://github.com/microsoft/terminal/pull/9092
Author: @DHowett
Created: 2/10/2021
Status: ✅ Merged
Merged: 2/10/2021
Merged by: @DHowett

Base: release-1.6 ← Head: dev/duhowett/spsp

📝 Commits (2)

  • 3306a04 Work around a (likely) optimizer issue plaguing SetPixelShaderPath
  • 63306c8 Add an issue link.

📊 Changes

2 files changed (+78 additions, -53 deletions)

View changed files

📝 src/cascadia/TerminalControl/TermControl.cpp (+76 -52)
📝 src/cascadia/TerminalControl/TermControl.h (+2 -1)

📄 Description

It appears as though the optimizer is generating a sequence of
instructions on x64 that results in a nonsense std::wstring_view being
passed to SetPixelShaderPath when it's converted from a winrt::hstring.

Initially, I suspected that the issue was in us caching _settings
before we broke off the coroutine to update settings on the UI thread. I
implemented a quick fix for this (applying values off the new settings
object while also storing it in the control instance), but it didn't
actually lead anywhere. I do think it's the right thing to do for code
health's sake. Pankaj already changed how this works in 1.7: we no
longer (ever) re-seat the _settings reference... we only ever change
its parentage. Whether this is right or wrong is not for this paragraph
to discuss.

Eventually, I started looking more closely at the time travel traces. It
seriously looks like the wstring_view is generated wrong to begin with.
The debugger points directly at return { L"", 0 }; (which is correct),
but the values we get immediately on the other side of the call are
something like { 0x7FFFFFFF, 0 } or { 0x0, 0x48454C4C }.

I moved just the call to SetPixelShaderPath into a separate function.
The bug miraculously disappeared when I marked it noinline. It
reappeared when the function was fully inlined.

To avoid any future issues, I moved the whole UI thread body of
UpdateSettings out into its own function, to be called only while on the
UI thread. This fixes the bug.

Closes #8723.
Closes #9064.

Validation Steps Performed

I found a repro (update the settings file every 0.5 seconds and resize
the terminal wildly while it's doing so) that would trigger the bug
within ~10 seconds. It stopped doing so.

🔄 This issue represents a GitHub Pull Request. It cannot be merged through Gitea due to API limitations.

## 📋 Pull Request Information **Original PR:** https://github.com/microsoft/terminal/pull/9092 **Author:** [@DHowett](https://github.com/DHowett) **Created:** 2/10/2021 **Status:** ✅ Merged **Merged:** 2/10/2021 **Merged by:** [@DHowett](https://github.com/DHowett) **Base:** `release-1.6` ← **Head:** `dev/duhowett/spsp` --- ### 📝 Commits (2) - [`3306a04`](https://github.com/microsoft/terminal/commit/3306a042dc00deebd1daecc8a16672b55220ec61) Work around a (likely) optimizer issue plaguing SetPixelShaderPath - [`63306c8`](https://github.com/microsoft/terminal/commit/63306c8fbf6f0205a75bfaa005ed57454c33c8fe) Add an issue link. ### 📊 Changes **2 files changed** (+78 additions, -53 deletions) <details> <summary>View changed files</summary> 📝 `src/cascadia/TerminalControl/TermControl.cpp` (+76 -52) 📝 `src/cascadia/TerminalControl/TermControl.h` (+2 -1) </details> ### 📄 Description It appears as though the optimizer is generating a sequence of instructions on x64 that results in a nonsense std::wstring_view being passed to SetPixelShaderPath when it's converted from a winrt::hstring. Initially, I suspected that the issue was in us caching `_settings` before we broke off the coroutine to update settings on the UI thread. I implemented a quick fix for this (applying values off the new settings object while also storing it in the control instance), but it didn't actually lead anywhere. I do think it's the right thing to do for code health's sake. Pankaj already changed how this works in 1.7: we no longer (ever) re-seat the `_settings` reference... we only ever change its parentage. Whether this is right or wrong is not for this paragraph to discuss. Eventually, I started looking more closely at the time travel traces. It seriously looks like the wstring_view is generated wrong to begin with. The debugger points directly at `return { L"", 0 };` (which is correct), but the values we get immediately on the other side of the call are something like `{ 0x7FFFFFFF, 0 }` or `{ 0x0, 0x48454C4C }`. I moved _just_ the call to SetPixelShaderPath into a separate function. The bug miraculously disappeared when I marked it **noinline**. It reappeared when the function was fully inlined. To avoid any future issues, I moved the whole UI thread body of UpdateSettings out into its own function, to be called only while on the UI thread. This fixes the bug. Closes #8723. Closes #9064. ## Validation Steps Performed I found a repro (update the settings file every 0.5 seconds and resize the terminal wildly while it's doing so) that would trigger the bug within ~10 seconds. It stopped doing so. --- <sub>🔄 This issue represents a GitHub Pull Request. It cannot be merged through Gitea due to API limitations.</sub>
claunia added the pull-request label 2026-01-31 09:21:49 +00:00
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Reference: starred/terminal#27413
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