Fix benchmark PR check (risc0#1711)

* Save results to S3 bucket, but only if pushing to main or a release
branch.
* Compare results from S3 bucket, based on current target branch.

.github/workflows/bench_pr.yml

@@ -43,6 +43,7 @@ jobs:
     env:
       FEATURE: ${{ matrix.feature }}
       DISABLE_S3: ${{ matrix.device == 'nvidia_rtx_3090_ti' }}
+      S3_BENCH_PATH: s3://risc0-ci-cache/public/bench/${{ github.base_ref || github.ref_name }}/fib/${{ matrix.os }}-${{ matrix.device }}
 
     steps:
       - uses: actions/checkout@v4
@@ -55,33 +56,33 @@ jobs:
           key: ${{ matrix.os }}-${{ matrix.feature }}
           disable_s3: ${{ env.DISABLE_S3 }}
 
+      - id: aws-creds
+        uses: aws-actions/configure-aws-credentials@v4
+        with:
+          aws-region: us-west-2
+          role-to-assume: arn:aws:iam::083632199359:role/gha_oidc_risc0_cache_public_access
+
+      - name: Download previous benchmark data
+        run: aws s3 cp $S3_BENCH_PATH/external.json ./cache/external.json
+
       - run: cargo run --bin cargo-risczero --no-default-features -- risczero install --version $RISC0_TOOLCHAIN_VERSION
 
       - name: Run benchmarks
         run: cargo bench --bench fib -F $FEATURE
 
-      - name: Download previous benchmark data
-        uses: actions/cache/restore@v4
-        with:
-          path: ./cache
-          key: fib-${{ runner.os }}-${{ matrix.device }}
-
       - name: Analyze benchmark results
         uses: risc0/[email protected]
         with:
           name: "${{ matrix.os }}-${{ matrix.device }}"
           tool: 'customBiggerIsBetter'
           output-file-path: target/hotbench/fib/benchmark.json
-          external-data-json-path: ./cache/benchmark.json
+          external-data-json-path: ./cache/external.json
           github-token: ${{ secrets.GITHUB_TOKEN }}
           alert-threshold: '120%'
           comment-on-alert: true
           fail-on-alert: true
           summary-always: true
 
-      - name: Save results
+      - name: Save current benchmark data
         if: github.event_name == 'push'
-        uses: actions/cache/save@v4
-        with:
-          path: ./cache
-          key: fib-${{ runner.os }}-${{ matrix.device }}
+        run: aws s3 cp ./cache/external.json $S3_BENCH_PATH/external.json