[mips][ptr-compr] Remove CompressedSigned MachineRepresentation

port 80dc6a33 https://crrev.com/c/1903445

Original Commit Message:

  [ptr-compr] Remove CompressedSigned MachineRepresentation

  Since smi-corrputing, TaggedSigned (aka known smis) only have the lower
  bits used. This renders CompressedSigned useless.

Change-Id: I3d656752bb81a09bd3985bd39ab9f656504f4da1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1911268
Auto-Submit: Zhao Jiazhong <zhaojiazhong-hf@loongson.cn>
Reviewed-by: Bill Budge <bbudge@chromium.org>
Commit-Queue: Bill Budge <bbudge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64925}

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

@@ -308,7 +308,6 @@ void InstructionSelector::VisitLoad(Node* node) {
     case MachineRepresentation::kSimd128:
       opcode = kMipsMsaLd;
       break;
-    case MachineRepresentation::kCompressedSigned:   // Fall through.
     case MachineRepresentation::kCompressedPointer:  // Fall through.
     case MachineRepresentation::kCompressed:         // Fall through.
     case MachineRepresentation::kWord64:             // Fall through.
@@ -391,7 +390,6 @@ void InstructionSelector::VisitStore(Node* node) {
       case MachineRepresentation::kSimd128:
         opcode = kMipsMsaSt;
         break;
-      case MachineRepresentation::kCompressedSigned:   // Fall through.
       case MachineRepresentation::kCompressedPointer:  // Fall through.
       case MachineRepresentation::kCompressed:         // Fall through.
       case MachineRepresentation::kWord64:             // Fall through.
@@ -1343,7 +1341,6 @@ void InstructionSelector::VisitUnalignedLoad(Node* node) {
     case MachineRepresentation::kSimd128:
       opcode = kMipsMsaLd;
       break;
-    case MachineRepresentation::kCompressedSigned:   // Fall through.
     case MachineRepresentation::kCompressedPointer:  // Fall through.
     case MachineRepresentation::kCompressed:         // Fall through.
     case MachineRepresentation::kWord64:             // Fall through.
@@ -1396,7 +1393,6 @@ void InstructionSelector::VisitUnalignedStore(Node* node) {
     case MachineRepresentation::kSimd128:
       opcode = kMipsMsaSt;
       break;
-    case MachineRepresentation::kCompressedSigned:   // Fall through.
     case MachineRepresentation::kCompressedPointer:  // Fall through.
     case MachineRepresentation::kCompressed:         // Fall through.
     case MachineRepresentation::kWord64:             // Fall through.

src/compiler/backend/mips64/instruction-selector-mips64.cc

@@ -389,7 +389,6 @@ void InstructionSelector::VisitLoad(Node* node) {
     case MachineRepresentation::kSimd128:
       opcode = kMips64MsaLd;
       break;
-    case MachineRepresentation::kCompressedSigned:   // Fall through.
     case MachineRepresentation::kCompressedPointer:  // Fall through.
     case MachineRepresentation::kCompressed:         // Fall through.
     case MachineRepresentation::kNone:
@@ -464,7 +463,6 @@ void InstructionSelector::VisitStore(Node* node) {
       case MachineRepresentation::kSimd128:
         opcode = kMips64MsaSt;
         break;
-      case MachineRepresentation::kCompressedSigned:   // Fall through.
       case MachineRepresentation::kCompressedPointer:  // Fall through.
       case MachineRepresentation::kCompressed:         // Fall through.
       case MachineRepresentation::kNone:
@@ -1691,7 +1689,6 @@ void InstructionSelector::VisitUnalignedLoad(Node* node) {
     case MachineRepresentation::kSimd128:
       opcode = kMips64MsaLd;
       break;
-    case MachineRepresentation::kCompressedSigned:   // Fall through.
     case MachineRepresentation::kCompressedPointer:  // Fall through.
     case MachineRepresentation::kCompressed:         // Fall through.
     case MachineRepresentation::kNone:
@@ -1744,7 +1741,6 @@ void InstructionSelector::VisitUnalignedStore(Node* node) {
     case MachineRepresentation::kSimd128:
       opcode = kMips64MsaSt;
       break;
-    case MachineRepresentation::kCompressedSigned:   // Fall through.
     case MachineRepresentation::kCompressedPointer:  // Fall through.
     case MachineRepresentation::kCompressed:         // Fall through.
     case MachineRepresentation::kNone: