github: Build with PGO

Using Frontend instrumentation rather than IR. This gives less
total speedup, but makes the profile much more usable for cross
other build targets.

Build the full Linux toolchain in stage1; this avoids needing to
rebuild runtimes for doing the profiling in stage2, and avoids
needing to wait for stage3 to complete before cross building
for Windows.

.github/workflows/build.yml

@@ -97,8 +97,7 @@ jobs:
             llvm-mingw-*.tar.xz
           retention-days: 7
 
-  # Build a cross compiler for Linux, targeting Windows.
+  linux-profile:
-  linux:
     if: (github.event_name != 'schedule') || (github.repository == 'mstorsjo/llvm-mingw')
     needs: [prepare, linux-stage1]
     runs-on: ubuntu-22.04
@@ -111,8 +110,42 @@ jobs:
         run: |
           tar -Jxf llvm-mingw-*.tar.xz
           rm llvm-mingw-*.tar.xz
+          mv llvm-mingw* llvm-mingw-stage1
+      - name: Build
+        env:
+          LLVM_VERSION: ${{needs.prepare.outputs.LLVM_VERSION}}
+          TAG: ${{needs.prepare.outputs.TAG}}
+          SOURCE_DATE_EPOCH: ${{needs.prepare.outputs.COMMIT_DATE_UNIX}}
+          BUILD_DATE: ${{needs.prepare.outputs.BUILD_DATE}}
+        run: |
+          # Build LLVM in mostly the same way as it is going to be built in the
+          # final form.
+          LLVM_CMAKEFLAGS="-DLLVM_ENABLE_LIBXML2=OFF -DLLDB_ENABLE_PYTHON=OFF" ./build-all.sh --profile $(pwd)/llvm-mingw-stage1
+      - uses: actions/upload-artifact@v4
+        with:
+          name: profile
+          path: |
+            profile.profdata
+          retention-days: 7
+
+  # Build a cross compiler for Linux, targeting Windows.
+  linux:
+    if: (github.event_name != 'schedule') || (github.repository == 'mstorsjo/llvm-mingw')
+    needs: [prepare, linux-stage1, linux-profile]
+    runs-on: ubuntu-22.04
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/download-artifact@v4
+        with:
+          name: linux-stage1-ucrt-x86_64-toolchain
+      - name: Unpack stage1 Clang
+        run: |
+          tar -Jxf llvm-mingw-*.tar.xz
+          rm llvm-mingw-*.tar.xz
           sudo mv llvm-mingw* /opt/llvm-mingw
-          echo /opt/llvm-mingw/bin >> $GITHUB_PATH
+      - uses: actions/download-artifact@v4
+        with:
+          name: profile
       - name: Build
         env:
           LLVM_VERSION: ${{needs.prepare.outputs.LLVM_VERSION}}
@@ -120,12 +153,10 @@ jobs:
           SOURCE_DATE_EPOCH: ${{needs.prepare.outputs.COMMIT_DATE_UNIX}}
           BUILD_DATE: ${{needs.prepare.outputs.BUILD_DATE}}
         run: |
-          mkdir -p install
-          cp -a /opt/llvm-mingw install
           # Skip dynamic library dependencies that might make it harder to
           # run the binaries on other distros (and that have little use within
           # llvm-mingw).
-          LLVM_CMAKEFLAGS="-DLLVM_ENABLE_LIBXML2=OFF -DLLDB_ENABLE_PYTHON=OFF" ./build-all.sh $(pwd)/install/llvm-mingw --with-clang --thinlto --llvm-only
+          LLVM_CMAKEFLAGS="-DLLVM_ENABLE_LIBXML2=OFF -DLLDB_ENABLE_PYTHON=OFF" ./build-all.sh /opt/llvm-mingw $(pwd)/install/llvm-mingw --thinlto --pgo --llvm-only
           .github/workflows/store-version.sh install/llvm-mingw/versions.txt
           ./test-libcxx-module.sh $(pwd)/install/llvm-mingw
           ./run-tests.sh $(pwd)/install/llvm-mingw
@@ -145,7 +176,7 @@ jobs:
   # libraries that were built in the 'linux' step above.
   linux-cross-aarch64:
     if: (github.event_name != 'schedule') || (github.repository == 'mstorsjo/llvm-mingw')
-    needs: [linux-stage1, prepare]
+    needs: [linux-stage1, linux-profile, prepare]
     runs-on: ubuntu-22.04
     steps:
       - uses: actions/checkout@v4
@@ -157,7 +188,9 @@ jobs:
           tar -Jxf llvm-mingw-*.tar.xz
           rm llvm-mingw-*.tar.xz
           sudo mv llvm-mingw* /opt/llvm-mingw
-          echo /opt/llvm-mingw/bin >> $GITHUB_PATH
+      - uses: actions/download-artifact@v4
+        with:
+          name: profile
       - name: Build
         env:
           LLVM_VERSION: ${{needs.prepare.outputs.LLVM_VERSION}}
@@ -165,7 +198,7 @@ jobs:
           SOURCE_DATE_EPOCH: ${{needs.prepare.outputs.COMMIT_DATE_UNIX}}
         run: |
           sudo apt-get update && sudo apt-get install g++-aarch64-linux-gnu
-          ./build-all.sh $(pwd)/install/llvm-mingw --no-runtimes --host=aarch64-linux-gnu --with-clang --thinlto
+          ./build-all.sh /opt/llvm-mingw $(pwd)/install/llvm-mingw --no-runtimes --host=aarch64-linux-gnu --thinlto --pgo
           .github/workflows/store-version.sh install/llvm-mingw/versions.txt
       - name: Assemble the cross-built toolchain
         run: |
@@ -259,7 +292,7 @@ jobs:
   # Build a cross compiler for macOS, targeting Windows.
   macos:
     if: (github.event_name != 'schedule') || (github.repository == 'mstorsjo/llvm-mingw')
-    needs: [prepare, macos-stage1]
+    needs: [prepare, macos-stage1, linux-profile]
     runs-on: macos-latest
     steps:
       - uses: actions/checkout@v4
@@ -271,7 +304,9 @@ jobs:
           tar -Jxf llvm-*.tar.xz
           rm llvm-*.tar.xz
           mv llvm* $HOME/llvm
-          echo $HOME/llvm/bin >> $GITHUB_PATH
+      - uses: actions/download-artifact@v4
+        with:
+          name: profile
       - name: Build
         env:
           LLVM_VERSION: ${{needs.prepare.outputs.LLVM_VERSION}}
@@ -285,8 +320,7 @@ jobs:
           # form. Therefore, autodetection will pick them up, but linking
           # universal binaries fails as those libraries are unavailable in the
           # other (x86_64) architecture form.
-          export SDKROOT=$(xcrun --show-sdk-path)
+          MACOS_REDIST=1 LLVM_CMAKEFLAGS="-DLLVM_ENABLE_ZSTD=OFF -DLLDB_ENABLE_PYTHON=OFF" ./build-all.sh $HOME/llvm $(pwd)/install/llvm-mingw --thinlto --pgo
-          MACOS_REDIST=1 LLVM_CMAKEFLAGS="-DLLVM_ENABLE_ZSTD=OFF -DLLDB_ENABLE_PYTHON=OFF" ./build-all.sh $(pwd)/install/llvm-mingw --with-clang --thinlto
           .github/workflows/store-version.sh install/llvm-mingw/versions.txt
           ./test-libcxx-module.sh $(pwd)/install/llvm-mingw
           ./run-tests.sh $(pwd)/install/llvm-mingw
@@ -363,7 +397,7 @@ jobs:
   # architectures). The binaries built here match actual releases quite closely.
   linux-cross-windows:
     if: (github.event_name != 'schedule') || (github.repository == 'mstorsjo/llvm-mingw')
-    needs: [linux-stage1, prepare]
+    needs: [linux-stage1, linux-profile, prepare]
     runs-on: ubuntu-latest
     strategy:
       fail-fast: false
@@ -384,6 +418,9 @@ jobs:
           sudo mv llvm-mingw* /opt/llvm-mingw
           echo /opt/llvm-mingw/bin >> $GITHUB_PATH
       - uses: actions/checkout@v4
+      - uses: actions/download-artifact@v4
+        with:
+          name: profile
       - name: Build
         env:
           LLVM_VERSION: ${{needs.prepare.outputs.LLVM_VERSION}}
@@ -394,7 +431,7 @@ jobs:
           BUILD_DATE: ${{needs.prepare.outputs.BUILD_DATE}}
         run: |
           sudo apt-get update && sudo apt-get install libltdl-dev swig autoconf-archive
-          ./build-cross-tools.sh /opt/llvm-mingw $(pwd)/install/llvm-mingw ${{matrix.arch}} --with-python --thinlto
+          ./build-cross-tools.sh /opt/llvm-mingw $(pwd)/install/llvm-mingw ${{matrix.arch}} --with-python --thinlto --pgo
           .github/workflows/store-version.sh install/llvm-mingw/versions.txt
           cd install
           NAME=llvm-mingw-$TAG-${{matrix.crt}}-${{matrix.arch}}
@@ -774,6 +811,7 @@ jobs:
           rm -rf msys2*
           rm -rf linux-stage1-*
           rm -rf macos-llvm*
+          rm -rf profile*
           mv *-toolchain/*.zip *-toolchain/*.tar.xz .
       - name: Upload binaries
         env: