[maglev] fix non-ptr-compr compilation on old compilers

Keyhan Vakil · V8 LUCI CQ · commit de611e69ad51 · 2023-12-15T15:11:48.000Z
When pointer compression is disabled, the preprocessor expands some static asserts to static_assert(false), which doesn't compile on compilers not implementing the C++ defect report CWG2518, notably clang before version 17 and gcc before version 13. Adding in part of the template parameter to the static assert prevents it from being evaluated immediately which fixes the compilation. Test: compiled with gcc-11 and clang-14 without pointer compression. Change-Id: I95ce29bdb1278e6dad9e592d6f9476395f8aeb59 Fixed: v8:14355 Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/5022760 Reviewed-by: Leszek Swirski <leszeks@chromium.org> Commit-Queue: Leszek Swirski <leszeks@chromium.org> Cr-Commit-Position: refs/heads/main@{#91553}
diff --git a/src/maglev/maglev-code-generator.cc b/src/maglev/maglev-code-generator.cc
@@ -420,7 +420,11 @@ class ParallelMoveResolver {
   void EmitMovesFromSource(RegisterT source_reg, GapMoveTargets&& targets) {
     DCHECK(moves_from_register_[source_reg.code()].is_empty());
     if constexpr (DecompressIfNeeded) {
-      static_assert(COMPRESS_POINTERS_BOOL);
+      // The DecompressIfNeeded clause is redundant with the if-constexpr above,
+      // but otherwise this code cannot be compiled by compilers not yet
+      // implementing CWG2518.
+      static_assert(DecompressIfNeeded && COMPRESS_POINTERS_BOOL);
+
       if (targets.needs_decompression == kNeedsDecompression) {
         __ DecompressTagged(source_reg, source_reg);
       }
@@ -463,7 +467,11 @@ class ParallelMoveResolver {
     // Decompress after the first move, subsequent moves reuse this register so
     // they're guaranteed to be decompressed.
     if constexpr (DecompressIfNeeded) {
-      static_assert(COMPRESS_POINTERS_BOOL);
+      // The DecompressIfNeeded clause is redundant with the if-constexpr above,
+      // but otherwise this code cannot be compiled by compilers not yet
+      // implementing CWG2518.
+      static_assert(DecompressIfNeeded && COMPRESS_POINTERS_BOOL);
+
       if (targets.needs_decompression == kNeedsDecompression) {
         __ DecompressTagged(register_with_slot_value, register_with_slot_value);
         targets.needs_decompression = kDoesNotNeedDecompression;
