mborland · Oct 7, 2026
diff --git a/.github/actions/build-softfloat-msvc/action.yml b/.github/actions/build-softfloat-msvc/action.yml
@@ -0,0 +1,122 @@
+# Part of the EDG Compiler Project, under the Apache License v2.0 with LLVM
+# Exceptions.
+# See https://edgcpp.org/LICENSE.txt for license information.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+#
+# Build SoftFloat (at the commit pinned in
+# dev_tools/docker/softfloat/SOFTFLOAT_COMMIT) with MSVC, leaving the headers
+# in softfloat/include and the library in softfloat/lib/softfloat.lib under
+# the workspace.  A cached build is reused when one is available.  The MSVC
+# developer environment must already be set up (e.g., with
+# ilammy/msvc-dev-cmd).
+
+name: Build SoftFloat (MSVC)
+description: Build (or restore from the cache) SoftFloat with MSVC.
+
+runs:
+  using: composite
+  steps:
+    - name: Read SoftFloat commit pin
+      id: softfloat-pin
+      shell: bash
+      run: |
+        echo "commit=$(tr -d '[:space:]' < dev_tools/docker/softfloat/SOFTFLOAT_COMMIT)" \
+          >> "${GITHUB_OUTPUT}"
+
+    - name: Cache SoftFloat
+      id: cache-softfloat
+      uses: actions/cache@v6
+      with:
+        path: softfloat
+        key: softfloat-msvc-win-${{ steps.softfloat-pin.outputs.commit }}
+
+    - name: Build SoftFloat (MSVC)
+      if: steps.cache-softfloat.outputs.cache-hit != 'true'
+      shell: bash
+      run: |
+        set -euo pipefail
+        commit="${{ steps.softfloat-pin.outputs.commit }}"
+        mkdir softfloat-src
+        git -C softfloat-src init
+        git -C softfloat-src remote add origin \
+          https://github.com/ucb-bar/berkeley-softfloat-3.git
+        git -C softfloat-src fetch --depth 1 origin "${commit}"
+        git -C softfloat-src checkout FETCH_HEAD
+
+        # EDG Windows SoftFloat build: cl + lib (not MinGW). Emit MSVC
+        # platform bits inline; derive sources.rsp from upstream's
+        # Win32-SSE2-MinGW Makefile (8086-SSE / non-FAST_INT64).
+        build_dir=softfloat-src/build/Win-MSVC
+        mkdir -p "${build_dir}"
+
+        cat > "${build_dir}/platform.h" <<'EOF'
+        /*============================================================================
+        MSVC platform header for SoftFloat. Keep free of GCC-only opts
+        (opts-GCC.h, SOFTFLOAT_BUILTIN_CLZ, SOFTFLOAT_INTRINSIC_INT128).
+        =============================================================================*/
+
+        #define LITTLEENDIAN 1
+
+        #ifdef _MSC_VER
+        #define INLINE static __inline
+        #else
+        #define INLINE static inline
+        #endif
+        EOF
+
+        # Strip the leading spaces YAML left in the heredoc body.
+        sed -i 's/^        //' "${build_dir}/platform.h"
+
+        cat > "${build_dir}/build.bat" <<'EOF'
+        REM In place of a Makefile, use this batch file to create softfloat.lib
+        REM Source paths live in sources.rsp to avoid CreateProcess length limits.
+
+        set LIB=softfloat.lib
+        set SOFTFLOAT_OPTS=-DSOFTFLOAT_ROUND_ODD -DINLINE_LEVEL=5 -DSOFTFLOAT_FAST_DIV32TO16 -DSOFTFLOAT_FAST_DIV64TO32
+        set SPECIALIZE_TYPE=8086-SSE
+        set SOURCE=..\..\source
+        set S=%SOURCE%\
+        set P=%SOURCE%\%SPECIALIZE_TYPE%\
+
+        del *.obj %LIB% 2>nul
+        cl -nologo -c -O2 -I. -I%S% -I%P% -I%S%include %SOFTFLOAT_OPTS% @sources.rsp
+        if errorlevel 1 exit /b 1
+        lib -nologo /out:%LIB% *.obj
+        if errorlevel 1 exit /b 1
+        EOF
+        sed -i 's/^        //' "${build_dir}/build.bat"
+
+        python - <<'PY'
+        import re
+        from pathlib import Path
+
+        makefile = Path(
+          'softfloat-src/build/Win32-SSE2-MinGW/Makefile'
+        ).read_text()
+
+        def section(name):
+          match = re.search(
+            rf'{name}\s*=\s*((?:.*\\\n)*.*)', makefile
+          )
+          return re.findall(r'(\w+)\$\(OBJ\)', match.group(1))
+
+        paths = (
+          [fr'..\..\source\{n}.c' for n in section('OBJS_PRIMITIVES')]
+          + [
+            fr'..\..\source\8086-SSE\{n}.c'
+            for n in section('OBJS_SPECIALIZE')
+          ]
+          + [fr'..\..\source\{n}.c' for n in section('OBJS_OTHERS')]
+        )
+        Path('softfloat-src/build/Win-MSVC/sources.rsp').write_text(
+          '\r\n'.join(paths) + '\r\n'
+        )
+        PY
+
+        cmd.exe //C "cd softfloat-src\\build\\Win-MSVC && build.bat"
+
+        mkdir -p softfloat/include softfloat/lib
+        cp softfloat-src/source/include/softfloat.h \
+           softfloat-src/source/include/softfloat_types.h \
+           softfloat/include/
+        cp softfloat-src/build/Win-MSVC/softfloat.lib softfloat/lib/
diff --git a/.github/workflows/self-compile-ci.yml b/.github/workflows/self-compile-ci.yml
@@ -0,0 +1,94 @@
+# Part of the EDG Compiler Project, under the Apache License v2.0 with LLVM
+# Exceptions.
+# See https://edgcpp.org/LICENSE.txt for license information.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+#
+# Check that the front end can still be built from the C that its
+# C-generating back end produces for the front end's own sources, which is how
+# C++ code is built for a system that has only a C compiler.  Each job builds
+# cpfe with the host C++ compiler, uses it to translate the front end to C,
+# builds cpfe-self from that C with the host C compiler, and then checks that
+# cpfe-self translates the front end to the same C as cpfe (see
+# src/cmake/cpfe-self/CMakeLists.txt).
+
+name: Self-Compile CI
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+
+jobs:
+  linux:
+    name: Linux ${{ matrix.name }}
+    runs-on: ubuntu-latest
+    timeout-minutes: 120
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - name: GCC x64
+            preset: linux-gcc-debug
+            build-dir: build/gcc
+            base: gcc
+          - name: GCC x32
+            preset: linux-i686-gcc-debug
+            build-dir: build/gcc-i686
+            base: gcc-i686
+          - name: Clang x64
+            preset: linux-clang-debug
+            build-dir: build/clang
+            base: clang
+    container:
+      image: docker.io/edgcpp/ci-runner:latest
+    defaults:
+      run:
+        shell: edg-container-exec "bash -eo pipefail {0}"
+    env:
+      EDG_BASE: ${{ github.workspace }}/bases/docker/dev-env/${{ matrix.base }}
+
+    steps:
+      - name: Check out repository
+        uses: actions/checkout@v7
+
+      - name: Configure ${{ matrix.preset }}
+        run: cmake --preset ${{ matrix.preset }} -DEDG_SELF_COMPILE=ON
+
+      - name: Build cpfe-self
+        run: cmake --build ${{ matrix.build-dir }} --target cpfe-self
+
+      - name: Check cpfe-self
+        run: cmake --build ${{ matrix.build-dir }} --target cpfe-self-check
+
+  windows-msvc:
+    name: Windows MSVC x64
+    runs-on: windows-latest
+    timeout-minutes: 120
+    env:
+      EDG_SOFTFLOAT_INCLUDE_PATH: ${{ github.workspace }}/softfloat/include
+      EDG_SOFTFLOAT_LIB_PATH: ${{ github.workspace }}/softfloat/lib/softfloat.lib
+
+    steps:
+      - name: Check out repository
+        uses: actions/checkout@v7
+
+      - name: Install Ninja
+        run: choco install ninja -y
+
+      - name: Set up MSVC developer environment
+        uses: ilammy/msvc-dev-cmd@v1
+
+      - name: Build SoftFloat
+        uses: ./.github/actions/build-softfloat-msvc
+
+      # The debug macro configuration does not use Microsoft bit-field
+      # allocation, so its layouts do not match the code that MSVC generates.
+      - name: Configure windows-msvc-release
+        run: cmake --preset windows-msvc-release -DEDG_SELF_COMPILE=ON
+
+      - name: Build cpfe-self
+        run: cmake --build build/msvc-release --target cpfe-self
+
+      - name: Check cpfe-self
+        run: cmake --build build/msvc-release --target cpfe-self-check
diff --git a/.github/workflows/strict-build-check.yml b/.github/workflows/strict-build-check.yml
@@ -26,113 +26,11 @@ jobs:
       - name: Install Ninja
         run: choco install ninja -y
 
-      - name: Read SoftFloat commit pin
-        id: softfloat-pin
-        shell: bash
-        run: |
-          echo "commit=$(tr -d '[:space:]' < dev_tools/docker/softfloat/SOFTFLOAT_COMMIT)" \
-            >> "${GITHUB_OUTPUT}"
-
-      - name: Cache SoftFloat
-        id: cache-softfloat
-        uses: actions/cache@v6
-        with:
-          path: softfloat
-          key: softfloat-msvc-win-${{ steps.softfloat-pin.outputs.commit }}
-
       - name: Set up MSVC developer environment
         uses: ilammy/msvc-dev-cmd@v1
 
-      - name: Build SoftFloat (MSVC)
-        if: steps.cache-softfloat.outputs.cache-hit != 'true'
-        shell: bash
-        run: |
-          set -euo pipefail
-          commit="${{ steps.softfloat-pin.outputs.commit }}"
-          mkdir softfloat-src
-          git -C softfloat-src init
-          git -C softfloat-src remote add origin \
-            https://github.com/ucb-bar/berkeley-softfloat-3.git
-          git -C softfloat-src fetch --depth 1 origin "${commit}"
-          git -C softfloat-src checkout FETCH_HEAD
-
-          # EDG Windows SoftFloat build: cl + lib (not MinGW). Emit MSVC
-          # platform bits inline; derive sources.rsp from upstream's
-          # Win32-SSE2-MinGW Makefile (8086-SSE / non-FAST_INT64).
-          build_dir=softfloat-src/build/Win-MSVC
-          mkdir -p "${build_dir}"
-
-          cat > "${build_dir}/platform.h" <<'EOF'
-          /*============================================================================
-          MSVC platform header for SoftFloat. Keep free of GCC-only opts
-          (opts-GCC.h, SOFTFLOAT_BUILTIN_CLZ, SOFTFLOAT_INTRINSIC_INT128).
-          =============================================================================*/
-
-          #define LITTLEENDIAN 1
-
-          #ifdef _MSC_VER
-          #define INLINE static __inline
-          #else
-          #define INLINE static inline
-          #endif
-          EOF
-
-          # Strip the leading spaces YAML left in the heredoc body.
-          sed -i 's/^          //' "${build_dir}/platform.h"
-
-          cat > "${build_dir}/build.bat" <<'EOF'
-          REM In place of a Makefile, use this batch file to create softfloat.lib
-          REM Source paths live in sources.rsp to avoid CreateProcess length limits.
-
-          set LIB=softfloat.lib
-          set SOFTFLOAT_OPTS=-DSOFTFLOAT_ROUND_ODD -DINLINE_LEVEL=5 -DSOFTFLOAT_FAST_DIV32TO16 -DSOFTFLOAT_FAST_DIV64TO32
-          set SPECIALIZE_TYPE=8086-SSE
-          set SOURCE=..\..\source
-          set S=%SOURCE%\
-          set P=%SOURCE%\%SPECIALIZE_TYPE%\
-
-          del *.obj %LIB% 2>nul
-          cl -nologo -c -O2 -I. -I%S% -I%P% -I%S%include %SOFTFLOAT_OPTS% @sources.rsp
-          if errorlevel 1 exit /b 1
-          lib -nologo /out:%LIB% *.obj
-          if errorlevel 1 exit /b 1
-          EOF
-          sed -i 's/^          //' "${build_dir}/build.bat"
-
-          python - <<'PY'
-          import re
-          from pathlib import Path
-
-          makefile = Path(
-            'softfloat-src/build/Win32-SSE2-MinGW/Makefile'
-          ).read_text()
-
-          def section(name):
-            match = re.search(
-              rf'{name}\s*=\s*((?:.*\\\n)*.*)', makefile
-            )
-            return re.findall(r'(\w+)\$\(OBJ\)', match.group(1))
-
-          paths = (
-            [fr'..\..\source\{n}.c' for n in section('OBJS_PRIMITIVES')]
-            + [
-              fr'..\..\source\8086-SSE\{n}.c'
-              for n in section('OBJS_SPECIALIZE')
-            ]
-            + [fr'..\..\source\{n}.c' for n in section('OBJS_OTHERS')]
-          )
-          Path('softfloat-src/build/Win-MSVC/sources.rsp').write_text(
-            '\r\n'.join(paths) + '\r\n'
-          )
-          PY
-
-          cmd.exe //C "cd softfloat-src\\build\\Win-MSVC && build.bat"
-
-          mkdir -p softfloat/include softfloat/lib
-          cp softfloat-src/source/include/softfloat.h \
-             softfloat-src/source/include/softfloat_types.h \
-             softfloat/include/
-          cp softfloat-src/build/Win-MSVC/softfloat.lib softfloat/lib/
+      - name: Build SoftFloat
+        uses: ./.github/actions/build-softfloat-msvc
 
       - name: Configure windows-msvc-release
         env:

diff --git a/BUILD.md b/BUILD.md
@@ -61,3 +61,28 @@ print:
 simply enter that directory and run the `ninja` build tool (or your specified
 build tool if you chose to use an alternative build generator).
 
+## Building the Front End from Generated C
+
+The C-generating back end allows C++ code to be built for systems that have
+only a C compiler, and the front end itself can be built that way.  Configuring
+with `-DEDG_SELF_COMPILE=ON` adds two targets:
+
+- `cpfe-self`: `cpfe` translates the front end's sources to C, and the C
+  compiler builds that C into `cpfe-self`.
+- `cpfe-self-check`: `cpfe-self` translates the same sources, and the result is
+  compared with the C generated by `cpfe` (ignoring the differences that are
+  expected between any two runs; see `dev_tools/bin/edg-compare-gen-c`).
+
+For example:
+
+```
+cmake --preset 'linux-gcc-debug' -DEDG_SELF_COMPILE=ON
+cmake --build build/gcc --target cpfe-self-check
+```
+
+This is supported with GCC, Clang, and MSVC and a single-configuration build
+generator such as ninja.  With MSVC, use a release preset: the debug
+configurations do not use Microsoft bit-field allocation, so the front end
+would not lay out structs as MSVC does.  The "Self-Compile CI" GitHub workflow
+runs these targets with GCC (x64 and x32) and Clang on Linux and with MSVC
+(x64) on Windows.