[ptr-compr] Loading a Tagged value decompresses too

This CL changes the Tagged loads when pointer compression is enabled.
It shouldn't affect anything for the time being since if we have pointer
compression enabled, we are going to be storing Compressed values. Later,
we will eliminate the Compressed representation and that it's where it
will come into effect.

Bug: v8:7703
Change-Id: I3dc774a0d6bada2955240e3fa318ff1f7ade6808
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1822637
Commit-Queue: Santiago Aboy Solanes <solanes@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64181}

src/compiler/backend/arm64/instruction-selector-arm64.cc

@@ -628,9 +628,24 @@ void InstructionSelector::VisitLoad(Node* node) {
 #else
       UNREACHABLE();
 #endif
+#ifdef V8_COMPRESS_POINTERS
+    case MachineRepresentation::kTaggedSigned:
+      opcode = kArm64LdrDecompressTaggedSigned;
+      immediate_mode = kLoadStoreImm32;
+      break;
+    case MachineRepresentation::kTaggedPointer:
+      opcode = kArm64LdrDecompressTaggedPointer;
+      immediate_mode = kLoadStoreImm32;
+      break;
+    case MachineRepresentation::kTagged:
+      opcode = kArm64LdrDecompressAnyTagged;
+      immediate_mode = kLoadStoreImm32;
+      break;
+#else
     case MachineRepresentation::kTaggedSigned:   // Fall through.
     case MachineRepresentation::kTaggedPointer:  // Fall through.
     case MachineRepresentation::kTagged:         // Fall through.
+#endif
     case MachineRepresentation::kWord64:
       opcode = kArm64Ldr;
       immediate_mode = kLoadStoreImm64;

src/compiler/backend/x64/instruction-selector-x64.cc

@@ -250,9 +250,21 @@ ArchOpcode GetLoadOpcode(LoadRepresentation load_rep) {
 #else
       UNREACHABLE();
 #endif
+#ifdef V8_COMPRESS_POINTERS
+    case MachineRepresentation::kTaggedSigned:
+      opcode = kX64MovqDecompressTaggedSigned;
+      break;
+    case MachineRepresentation::kTaggedPointer:
+      opcode = kX64MovqDecompressTaggedPointer;
+      break;
+    case MachineRepresentation::kTagged:
+      opcode = kX64MovqDecompressAnyTagged;
+      break;
+#else
     case MachineRepresentation::kTaggedSigned:   // Fall through.
     case MachineRepresentation::kTaggedPointer:  // Fall through.
     case MachineRepresentation::kTagged:         // Fall through.
+#endif
     case MachineRepresentation::kWord64:
       opcode = kX64Movq;
       break;