CI: Build and test both x86-64 and AArch64 macOS

Fixes #1061.

.github/ci.sh

@@ -121,14 +121,14 @@ sign() {
 
 zip_dist() {
   : "${VERSION?VERSION is required as an environment variable}"
-  name="${name:-"cryptol-$VERSION-$OS_TAG-x86_64"}"
+  name="${name:-"cryptol-$VERSION-$OS_TAG-$ARCH_TAG"}"
   cp -r dist "$name"
   tar -cvzf "$name".tar.gz "$name"
 }
 
 zip_dist_with_solvers() {
   : "${VERSION?VERSION is required as an environment variable}"
-  name="${name:-"cryptol-$VERSION-$OS_TAG-x86_64"}"
+  name="${name:-"cryptol-$VERSION-$OS_TAG-$ARCH_TAG"}"
   sname="${name}-with-solvers"
   cp "$(which abc)"        dist/bin/
   cp "$(which cvc4)"       dist/bin/

.github/workflows/ci.yml

@@ -64,17 +64,10 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-22.04, macos-12, windows-2019]
+        os: [ubuntu-22.04]
         ghc-version: ["9.2.8", "9.4.7", "9.6.2"]
         cabal: [ '3.10.1.0' ]
         run-tests: [true]
-        exclude:
-          - os: windows-2019
-            ghc-version: 9.4.7
-            run-tests: true
-          - os: windows-2019
-            ghc-version: 9.6.2
-            run-tests: true
         include:
           # We include one job from an older Ubuntu LTS release to increase our
           # coverage of possible Linux configurations. Since we already run the
@@ -82,6 +75,19 @@ jobs:
           - os: ubuntu-20.04
             ghc-version: 9.2.8
             run-tests: false
+          # Windows and macOS CI runners are more expensive than Linux runners,
+          # so we only build one particular GHC version to test them on. We
+          # include both an x86-64 macOS runner (macos-12) as well as an AArch64
+          # macOS runner (macos-14).
+          - os: windows-2019
+            ghc-version: 9.2.8
+            run-tests: true
+          - os: macos-12
+            ghc-version: 9.2.8
+            run-tests: true
+          - os: macos-14
+            ghc-version: 9.2.8
+            run-tests: true
     outputs:
       test-lib-json: ${{ steps.test-lib.outputs.targets-json }}
     env:
@@ -181,19 +187,21 @@ jobs:
 
       - shell: bash
         run: |
-          NAME="${{ needs.config.outputs.name }}-${{ matrix.os }}-x86_64"
+          NAME="${{ needs.config.outputs.name }}-${{ matrix.os }}-${{ runner.arch }}"
           echo "NAME=$NAME" >> $GITHUB_ENV
           .github/ci.sh zip_dist $NAME
         env:
           OS_TAG: ${{ matrix.os }}
+          ARCH_TAG: ${{ runner.arch }}
 
       - shell: bash
         run: |
-          NAME="${{ needs.config.outputs.name }}-${{ matrix.os }}-x86_64"
+          NAME="${{ needs.config.outputs.name }}-${{ matrix.os }}-${{ runner.arch }}"
           echo "NAME=$NAME" >> $GITHUB_ENV
           .github/ci.sh zip_dist_with_solvers $NAME
         env:
           OS_TAG: ${{ matrix.os }}
+          ARCH_TAG: ${{ runner.arch }}
 
       - if: github.event.pull_request.head.repo.fork == false
         shell: bash
@@ -256,7 +264,7 @@ jobs:
       matrix:
         suite: [test-lib]
         target: ${{ fromJson(needs.build.outputs.test-lib-json) }}
-        os: [ubuntu-22.04, macos-12, windows-2019]
+        os: [ubuntu-22.04, macos-14, windows-2019]
         continue-on-error: [false]
         include:
           - suite: rpc
@@ -280,6 +288,24 @@ jobs:
         with:
           ghc-version: '9.2.8'
 
+      # Homebrew installs packages in different directories depending on which
+      # macOS architecture you are using:
+      #
+      # * /usr/local (X64)
+      # * /opt/homebrew (ARM64)
+      #
+      # Clang automatically searches in /usr/local without any additional setup,
+      # but it doesn't know about /opt/homebrew. As such, we have to teach Clang
+      # to do so by setting the appropriate environment variables.
+      #
+      # This step is important for the FFI unit tests, which rely on a
+      # Homebrew-provided version of gmp.
+      - name: Teach Clang about Homebrew paths (macOS ARM64)
+        run: |
+          echo "CPATH=/opt/homebrew/include" >> $GITHUB_ENV
+          echo "LIBRARY_PATH=/opt/homebrew/lib" >> $GITHUB_ENV
+        if: matrix.suite == 'test-lib' && runner.os == 'macOS' && runner.arch == 'ARM64'
+
       - name: Install dependencies (Windows)
         uses: msys2/setup-msys2@v2
         with:

src/Cryptol/Backend/Arch.hs

@@ -17,9 +17,9 @@ module Cryptol.Backend.Arch where
 -- experiments show that it's somewhere under 2^37 at least on 64-bit
 -- Mac OS X.
 maxBigIntWidth :: Integer
-#if i386_HOST_ARCH
+#if defined(i386_HOST_ARCH)
 maxBigIntWidth = 2^(32 :: Integer) - 0x1
-#elif x86_64_HOST_ARCH
+#elif defined(x86_64_HOST_ARCH) || defined(aarch64_HOST_ARCH)
 maxBigIntWidth = 2^(37 :: Integer) - 0x100
 #else
 -- Because GHC doesn't seem to define a CPP macro that will portably