[wasm][turbofan] Load 32-bit values more efficiently

backes · V8 LUCI CQ · commit a38209949fcb · 2022-12-12T21:36:50.000Z
When loading a 32-bit value from the stack, just load 32 bit and zero-extend them into the target register, instead of loading the full 64 bits. As there are things to fix (see https://crbug.com/1356461), we only enable this optimization for Wasm for now. R=jkummerow@chromium.org Bug: chromium:1395604, chromium:1356461, v8:13581 Change-Id: Ibdd2d80704973362906aec9b38faa762d3b43f3f Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/4097424 Reviewed-by: Jakob Kummerow <jkummerow@chromium.org> Reviewed-by: Maya Lekova <mslekova@chromium.org> Commit-Queue: Clemens Backes <clemensb@chromium.org> Cr-Commit-Position: refs/heads/main@{#84796}
diff --git a/src/compiler/backend/x64/code-generator-x64.cc b/src/compiler/backend/x64/code-generator-x64.cc
@@ -5335,7 +5335,22 @@ void CodeGenerator::AssembleMove(InstructionOperand* source,
     case MoveType::kStackToRegister: {
       Operand src = g.ToOperand(source);
       if (source->IsStackSlot()) {
-        __ movq(g.ToRegister(destination), src);
+        MachineRepresentation mr =
+            LocationOperand::cast(source)->representation();
+        const bool is_32_bit = mr == MachineRepresentation::kWord32 ||
+                               mr == MachineRepresentation::kCompressed ||
+                               mr == MachineRepresentation::kCompressedPointer;
+        // TODO(13581): Fix this for other code kinds (see
+        // https://crbug.com/1356461).
+        if (code_kind() == CodeKind::WASM_FUNCTION && is_32_bit) {
+          // When we need only 32 bits, move only 32 bits. Benefits:
+          // - Save a byte here and there (depending on the destination
+          //   register; "movl eax, ..." is smaller than "movq rax, ...").
+          // - Safeguard against accidental decompression of compressed slots.
+          __ movl(g.ToRegister(destination), src);
+        } else {
+          __ movq(g.ToRegister(destination), src);
+        }
       } else {
         DCHECK(source->IsFPStackSlot());
         XMMRegister dst = g.ToDoubleRegister(destination);
