diff --git a/.github/actions/setup-llvm/action.yml b/.github/actions/setup-llvm/action.yml
new file mode 100644
index 0000000000..1791fb0ac4
--- /dev/null
+++ b/.github/actions/setup-llvm/action.yml
@@ -0,0 +1,62 @@
+name: Set up LLVM
+description: Restore or build the LLVM source and build directories
+
+inputs:
+  cache-suffix:
+    description: Suffix for the LLVM cache keys
+    required: false
+    default: linux-asserts-v1
+  assertions:
+    description: Enable LLVM assertions
+    required: false
+    default: "1"
+
+runs:
+  using: composite
+  steps:
+    - name: Restore LLVM source cache
+      uses: actions/cache/restore@v5
+      id: cache-llvm-source
+      with:
+        key: llvm-source-22-${{ inputs.cache-suffix }}-${{ hashFiles('llvm-version.txt') }}
+        path: |
+          llvm-project/clang/lib/Headers
+          llvm-project/clang/include
+          llvm-project/compiler-rt
+          llvm-project/lld/include
+          llvm-project/llvm/include
+    - name: Download LLVM source
+      if: steps.cache-llvm-source.outputs.cache-hit != 'true'
+      shell: bash
+      run: make llvm-source
+    - name: Save LLVM source cache
+      uses: actions/cache/save@v5
+      if: steps.cache-llvm-source.outputs.cache-hit != 'true'
+      with:
+        key: ${{ steps.cache-llvm-source.outputs.cache-primary-key }}
+        path: |
+          llvm-project/clang/lib/Headers
+          llvm-project/clang/include
+          llvm-project/compiler-rt
+          llvm-project/lld/include
+          llvm-project/llvm/include
+    - name: Restore LLVM build cache
+      uses: actions/cache/restore@v5
+      id: cache-llvm-build
+      with:
+        key: llvm-build-22-${{ inputs.cache-suffix }}-${{ hashFiles('llvm-version.txt') }}
+        path: llvm-build
+    - name: Build LLVM
+      if: steps.cache-llvm-build.outputs.cache-hit != 'true'
+      shell: bash
+      run: |
+        rm -rf llvm-project
+        make llvm-source
+        make llvm-build ASSERT=${{ inputs.assertions }}
+        find llvm-build -name CMakeFiles -prune -exec rm -r '{}' \;
+    - name: Save LLVM build cache
+      uses: actions/cache/save@v5
+      if: steps.cache-llvm-build.outputs.cache-hit != 'true'
+      with:
+        key: ${{ steps.cache-llvm-build.outputs.cache-primary-key }}
+        path: llvm-build
diff --git a/.github/workflows/linux.yml b/.github/workflows/linux.yml
index 3465f020d5..ec2006e030 100644
--- a/.github/workflows/linux.yml
+++ b/.github/workflows/linux.yml
@@ -264,53 +264,7 @@ jobs:
             "https://github.com/espressif/qemu/releases/download/$release/$archive"
           tar -xJf "$RUNNER_TEMP/$archive" -C "$RUNNER_TEMP"
           echo "$RUNNER_TEMP/qemu/bin" >> "$GITHUB_PATH"
-      - name: Restore LLVM source cache
-        uses: actions/cache/restore@v5
-        id: cache-llvm-source
-        with:
-          key: llvm-source-22-linux-asserts-v1-${{ hashFiles('llvm-version.txt') }}
-          path: |
-            llvm-project/clang/lib/Headers
-            llvm-project/clang/include
-            llvm-project/compiler-rt
-            llvm-project/lld/include
-            llvm-project/llvm/include
-      - name: Download LLVM source
-        if: steps.cache-llvm-source.outputs.cache-hit != 'true'
-        run: make llvm-source
-      - name: Save LLVM source cache
-        uses: actions/cache/save@v5
-        if: steps.cache-llvm-source.outputs.cache-hit != 'true'
-        with:
-          key: ${{ steps.cache-llvm-source.outputs.cache-primary-key }}
-          path: |
-            llvm-project/clang/lib/Headers
-            llvm-project/clang/include
-            llvm-project/compiler-rt
-            llvm-project/lld/include
-            llvm-project/llvm/include
-      - name: Restore LLVM build cache
-        uses: actions/cache/restore@v5
-        id: cache-llvm-build
-        with:
-          key: llvm-build-22-linux-asserts-v1-${{ hashFiles('llvm-version.txt') }}
-          path: llvm-build
-      - name: Build LLVM
-        if: steps.cache-llvm-build.outputs.cache-hit != 'true'
-        run: |
-          # fetch LLVM source
-          rm -rf llvm-project
-          make llvm-source
-          # build!
-          make llvm-build ASSERT=1
-          # Remove unnecessary object files (to reduce cache size).
-          find llvm-build -name CMakeFiles -prune -exec rm -r '{}' \;
-      - name: Save LLVM build cache
-        uses: actions/cache/save@v5
-        if: steps.cache-llvm-build.outputs.cache-hit != 'true'
-        with:
-          key: ${{ steps.cache-llvm-build.outputs.cache-primary-key }}
-          path: llvm-build
+      - uses: ./.github/actions/setup-llvm
       - name: Cache Binaryen
         uses: actions/cache@v5
         id: cache-binaryen
diff --git a/.github/workflows/sizediff.yml b/.github/workflows/sizediff.yml
index 984e8370c6..f2e326cbad 100644
--- a/.github/workflows/sizediff.yml
+++ b/.github/workflows/sizediff.yml
@@ -30,16 +30,7 @@ jobs:
           submodules: true
       - name: Install apt dependencies
         run: ./.github/workflows/sizediff-install-pkgs.sh
-      - name: Restore LLVM source cache
-        uses: actions/cache@v5
-        id: cache-llvm-source
-        with:
-          key: llvm-source-22-sizediff-v1-${{ hashFiles('llvm-version.txt') }}
-          path: |
-            llvm-project/compiler-rt
-      - name: Download LLVM source
-        if: steps.cache-llvm-source.outputs.cache-hit != 'true'
-        run: make llvm-source
+      - uses: ./.github/actions/setup-llvm
       - name: Cache Go
         uses: actions/cache@v5
         with:
@@ -51,26 +42,44 @@ jobs:
       - name: Download drivers repo
         run: git clone https://github.com/tinygo-org/drivers.git
       - name: Save HEAD
-        run: git branch github-actions-saved-HEAD HEAD
+        id: pr
+        run: |
+          git branch github-actions-saved-HEAD HEAD
+          cp -r .github/actions/setup-llvm .github/actions/setup-llvm-base
+          echo "llvm_version=$(cat llvm-version.txt)" >> "$GITHUB_OUTPUT"
 
       # Compute sizes for the PR branch
       - name: Build tinygo binary for the PR branch
-        run: go install
+        run: make tinygo ASSERT=1
       - name: Determine binary sizes on the PR branch
-        run: (cd drivers; make smoke-test XTENSA=0 | tee sizes-pr.txt)
+        run: |
+          set -o pipefail
+          export PATH="$PWD/build:$PATH"
+          (cd drivers; make smoke-test | tee sizes-pr.txt)
 
       # Compute sizes for the dev branch
       - name: Checkout dev branch
+        id: dev
         run: |
           git reset --hard origin/dev
-          git checkout --no-recurse-submodules `git merge-base HEAD origin/dev`
+          git checkout --no-recurse-submodules "${{ github.event.pull_request.base.sha }}"
+          echo "llvm_version=$(cat llvm-version.txt)" >> "$GITHUB_OUTPUT"
       - name: Install apt dependencies on the dev branch
         # this is only needed on a PR that changes the LLVM version
         run: ./.github/workflows/sizediff-install-pkgs.sh
+      - name: Remove LLVM build for the PR branch
+        if: steps.pr.outputs.llvm_version != steps.dev.outputs.llvm_version
+        run: rm -rf llvm-build llvm-project
+      - name: Set up LLVM for the dev branch
+        uses: ./.github/actions/setup-llvm-base
+        if: steps.pr.outputs.llvm_version != steps.dev.outputs.llvm_version
       - name: Build tinygo binary for the dev branch
-        run: go install
+        run: make tinygo ASSERT=1
       - name: Determine binary sizes on the dev branch
-        run: (cd drivers; make smoke-test XTENSA=0 | tee sizes-dev.txt)
+        run: |
+          set -o pipefail
+          export PATH="$PWD/build:$PATH"
+          (cd drivers; make smoke-test | tee sizes-dev.txt)
 
       # Create comment
       # TODO: add a summary, something like: