PPC/s390: [ptr-compr] Remove CompressedSigned MachineRepresentation

Port 80dc6a33

Original Commit Message:

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

R=solanes@chromium.org, joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com
BUG=
LOG=N

Change-Id: Ia3daa8e8fe60e8046784436b3dfcdad63b6597c6
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1907442Reviewed-by: Junliang Yan <jyan@ca.ibm.com>
Commit-Queue: Milad Farazmand <miladfar@ca.ibm.com>
Cr-Commit-Position: refs/heads/master@{#64891}

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

@@ -198,7 +198,6 @@ void InstructionSelector::VisitLoad(Node* node) {
       opcode = kPPC_LoadWord64;
       mode = kInt16Imm_4ByteAligned;
       break;
-    case MachineRepresentation::kCompressedSigned:   // Fall through.
     case MachineRepresentation::kCompressedPointer:  // Fall through.
     case MachineRepresentation::kCompressed:         // Fall through.
     case MachineRepresentation::kSimd128:  // Fall through.
@@ -322,7 +321,6 @@ void InstructionSelector::VisitStore(Node* node) {
 #else
       case MachineRepresentation::kWord64:  // Fall through.
 #endif
-      case MachineRepresentation::kCompressedSigned:   // Fall through.
       case MachineRepresentation::kCompressedPointer:  // Fall through.
       case MachineRepresentation::kCompressed:         // Fall through.
       case MachineRepresentation::kSimd128:  // Fall through.

src/compiler/backend/s390/instruction-selector-s390.cc

@@ -303,7 +303,6 @@ ArchOpcode SelectLoadOpcode(Node* node) {
 #else
     case MachineRepresentation::kWord64:  // Fall through.
 #endif
-    case MachineRepresentation::kCompressedSigned:   // Fall through.
     case MachineRepresentation::kCompressedPointer:  // Fall through.
     case MachineRepresentation::kCompressed:         // Fall through.
     case MachineRepresentation::kSimd128:  // Fall through.
@@ -757,7 +756,6 @@ static void VisitGeneralStore(
       case MachineRepresentation::kTaggedSigned:       // Fall through.
       case MachineRepresentation::kTaggedPointer:      // Fall through.
       case MachineRepresentation::kTagged:             // Fall through.
-      case MachineRepresentation::kCompressedSigned:   // Fall through.
       case MachineRepresentation::kCompressedPointer:  // Fall through.
       case MachineRepresentation::kCompressed:         // Fall through.
 #endif
@@ -772,7 +770,6 @@ static void VisitGeneralStore(
       case MachineRepresentation::kTaggedSigned:       // Fall through.
       case MachineRepresentation::kTaggedPointer:      // Fall through.
       case MachineRepresentation::kTagged:             // Fall through.
-      case MachineRepresentation::kCompressedSigned:   // Fall through.
       case MachineRepresentation::kCompressedPointer:  // Fall through.
       case MachineRepresentation::kCompressed:         // Fall through.
       case MachineRepresentation::kWord64: