[wasm-simd][arm64] Optimize load extends to remove add

For load extends, we can use Ldr, which does not require us to manually
calculate address - ld1r uses post-index, so we have to add the index
ourselves.

By checking the operation in the instruction-selector, we can set the
addressing mode for load extends to be MRR, then use Ldr in the codegen.

Bug: v8:9886
Change-Id: Ibcd22fa719cd6dafd2fd06e68066960db249b57a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2207656Reviewed-by: Deepti Gandluri <gdeepti@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67912}

src/compiler/backend/arm64/code-generator-arm64.cc

@@ -2550,32 +2550,32 @@ CodeGenerator::CodeGenResult CodeGenerator::AssembleArchInstruction(
       break;
     }
     case kArm64I16x8Load8x8S: {
-      __ ld1(i.OutputSimd128Register().V8B(), i.MemoryOperand(0));
+      __ Ldr(i.OutputSimd128Register().V8B(), i.MemoryOperand(0));
       __ Sxtl(i.OutputSimd128Register().V8H(), i.OutputSimd128Register().V8B());
       break;
     }
     case kArm64I16x8Load8x8U: {
-      __ ld1(i.OutputSimd128Register().V8B(), i.MemoryOperand(0));
+      __ Ldr(i.OutputSimd128Register().V8B(), i.MemoryOperand(0));
       __ Uxtl(i.OutputSimd128Register().V8H(), i.OutputSimd128Register().V8B());
       break;
     }
     case kArm64I32x4Load16x4S: {
-      __ ld1(i.OutputSimd128Register().V4H(), i.MemoryOperand(0));
+      __ Ldr(i.OutputSimd128Register().V4H(), i.MemoryOperand(0));
       __ Sxtl(i.OutputSimd128Register().V4S(), i.OutputSimd128Register().V4H());
       break;
     }
     case kArm64I32x4Load16x4U: {
-      __ ld1(i.OutputSimd128Register().V4H(), i.MemoryOperand(0));
+      __ Ldr(i.OutputSimd128Register().V4H(), i.MemoryOperand(0));
       __ Uxtl(i.OutputSimd128Register().V4S(), i.OutputSimd128Register().V4H());
       break;
     }
     case kArm64I64x2Load32x2S: {
-      __ ld1(i.OutputSimd128Register().V2S(), i.MemoryOperand(0));
+      __ Ldr(i.OutputSimd128Register().V2S(), i.MemoryOperand(0));
       __ Sxtl(i.OutputSimd128Register().V2D(), i.OutputSimd128Register().V2S());
       break;
     }
     case kArm64I64x2Load32x2U: {
-      __ ld1(i.OutputSimd128Register().V2S(), i.MemoryOperand(0));
+      __ Ldr(i.OutputSimd128Register().V2S(), i.MemoryOperand(0));
       __ Uxtl(i.OutputSimd128Register().V2D(), i.OutputSimd128Register().V2S());
       break;
     }

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

@@ -608,18 +608,23 @@ void EmitLoad(InstructionSelector* selector, Node* node, InstructionCode opcode,
 void InstructionSelector::VisitLoadTransform(Node* node) {
   LoadTransformParameters params = LoadTransformParametersOf(node->op());
   InstructionCode opcode = kArchNop;
+  bool require_add = false;
   switch (params.transformation) {
     case LoadTransformation::kS8x16LoadSplat:
       opcode = kArm64S8x16LoadSplat;
+      require_add = true;
       break;
     case LoadTransformation::kS16x8LoadSplat:
       opcode = kArm64S16x8LoadSplat;
+      require_add = true;
       break;
     case LoadTransformation::kS32x4LoadSplat:
       opcode = kArm64S32x4LoadSplat;
+      require_add = true;
       break;
     case LoadTransformation::kS64x2LoadSplat:
       opcode = kArm64S64x2LoadSplat;
+      require_add = true;
       break;
     case LoadTransformation::kI16x8Load8x8S:
       opcode = kArm64I16x8Load8x8S;
@@ -655,6 +660,7 @@ void InstructionSelector::VisitLoadTransform(Node* node) {
   inputs[1] = g.UseRegister(index);
   outputs[0] = g.DefineAsRegister(node);
 
+  if (require_add) {
     // ld1r uses post-index, so construct address first.
     // TODO(v8:9886) If index can be immediate, use vldr without this add.
     InstructionOperand addr = g.TempRegister();
@@ -662,6 +668,9 @@ void InstructionSelector::VisitLoadTransform(Node* node) {
     inputs[0] = addr;
     inputs[1] = g.TempImmediate(0);
     opcode |= AddressingModeField::encode(kMode_MRI);
+  } else {
+    opcode |= AddressingModeField::encode(kMode_MRR);
+  }
   Emit(opcode, 1, outputs, 2, inputs);
 }