From c844d0b677f9346db53730aceca272bf2b02df3c Mon Sep 17 00:00:00 2001
From: Damyan Pepper <damyanp@microsoft.com>
Date: Thu, 19 Feb 2026 17:40:29 +0000
Subject: [PATCH 1/2] Fix GCC 13 Release build test failures (#7364)

GCC 13 (e.g. 13.3.0 shipped with Ubuntu 24.04) has a known miscompilation
bug in -funswitch-loops (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109934)
that causes widespread test failures when building DXC at -O3.

Disable -funswitch-loops for GCC 13, and update the CI pipeline from
Ubuntu-22.04 to Ubuntu-24.04 (which ships GCC 13 as default), removing
the workaround from #7365.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 azure-pipelines.yml                   | 2 +-
 cmake/modules/HandleLLVMOptions.cmake | 8 ++++++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/azure-pipelines.yml b/azure-pipelines.yml
index 5b0c5d3791..12174fe6e1 100644
--- a/azure-pipelines.yml
+++ b/azure-pipelines.yml
@@ -78,7 +78,7 @@ stages:
 
     variables:
       macOS: macOS-latest
-      linux: Ubuntu-22.04 # FIXME: #7364, DXC does not build correctly with GCC 13+
+      linux: Ubuntu-24.04
 
     strategy:
       matrix:
diff --git a/cmake/modules/HandleLLVMOptions.cmake b/cmake/modules/HandleLLVMOptions.cmake
index f838acccf5..d5769abce7 100644
--- a/cmake/modules/HandleLLVMOptions.cmake
+++ b/cmake/modules/HandleLLVMOptions.cmake
@@ -16,6 +16,14 @@ if(NOT LLVM_FORCE_USE_OLD_TOOLCHAIN)
     if(CMAKE_CXX_COMPILER_VERSION VERSION_LESS 4.7)
       message(FATAL_ERROR "Host GCC version must be at least 4.7!")
     endif()
+    # GCC 13 has a known miscompilation bug in -funswitch-loops
+    # (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109934) that causes
+    # widespread test failures at -O3. Disable -funswitch-loops for GCC 13.
+    if(CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 13.0 AND
+       CMAKE_CXX_COMPILER_VERSION VERSION_LESS 14.0)
+      add_compile_options(-fno-unswitch-loops)
+      message(STATUS "Disabling -funswitch-loops due to GCC 13 miscompilation bug (PR109934)")
+    endif()
   elseif(CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
     if(CMAKE_CXX_COMPILER_VERSION VERSION_LESS 3.1)
       message(FATAL_ERROR "Host Clang version must be at least 3.1!")

From 4a8caffb44dfc9c76f78ff777ae827f9a3e87d64 Mon Sep 17 00:00:00 2001
From: Damyan Pepper <damyanp@microsoft.com>
Date: Thu, 19 Feb 2026 14:29:58 -0800
Subject: [PATCH 2/2] Use default GCC from build image instead of gcc-9

Remove explicit gcc version suffix from Linux_Gcc_Release and
Linux_Gcc_Debug builds, and remove the apt-get install step for g++.
This lets the builds use whichever GCC ships with the build image.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 azure-pipelines.yml | 13 ++++---------
 1 file changed, 4 insertions(+), 9 deletions(-)

diff --git a/azure-pipelines.yml b/azure-pipelines.yml
index 12174fe6e1..c4f7195066 100644
--- a/azure-pipelines.yml
+++ b/azure-pipelines.yml
@@ -99,13 +99,13 @@ stages:
         Linux_Gcc_Release:
           image: ${{ variables.linux }}
           configuration: Release
-          CC: gcc-9
-          CXX: g++-9
+          CC: gcc
+          CXX: g++
         Linux_Gcc_Debug:
           image: ${{ variables.linux }}
           configuration: Debug
-          CC: gcc-9
-          CXX: g++-9
+          CC: gcc
+          CXX: g++
           CMAKE_OPTS: -DLLVM_USE_SPLIT_DWARF=On
         MacOS_Clang_Release:
           image: ${{ variables.macOS }}
@@ -144,11 +144,6 @@ stages:
       displayName: 'Installing dependencies'
       condition: eq(variables['image'], variables['linux'])
 
-    - bash: |
-        sudo apt-get install g++-9 -y
-      displayName: 'Installing g++-9'
-      condition: and(eq(variables['CXX'], 'g++-9'), eq(variables['image'], variables['linux']))
-
     - bash: |
         brew update
         brew install ninja