[arm] Match LoadStackPointer with comparison.

When encountering a LoadStackPointer input to a comparison, generate a register
LocationOperand that points to the stack pointer. This can avoid unnecessary
spilling of the stack pointer.

Change-Id: Ifd1a5aaf22c9c594e653cf4689ba46587811c4d0
Reviewed-on: https://chromium-review.googlesource.com/1055568Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53161}

src/compiler/arm/instruction-selector-arm.cc

@@ -73,6 +73,17 @@ class ArmOperandGenerator : public OperandGenerator {
     }
     return false;
   }
+
+  // Use the stack pointer if the node is LoadStackPointer, otherwise assign a
+  // register.
+  InstructionOperand UseRegisterOrStackPointer(Node* node) {
+    if (node->opcode() == IrOpcode::kLoadStackPointer) {
+      return LocationOperand(LocationOperand::EXPLICIT,
+                             LocationOperand::REGISTER,
+                             MachineRepresentation::kWord32, sp.code());
+    }
+    return UseRegister(node);
+  }
 };
 
 
@@ -1679,17 +1690,17 @@ void VisitWordCompare(InstructionSelector* selector, Node* node,
 
   if (TryMatchImmediateOrShift(selector, &opcode, m.right().node(),
                                &input_count, &inputs[1])) {
-    inputs[0] = g.UseRegister(m.left().node());
+    inputs[0] = g.UseRegisterOrStackPointer(m.left().node());
     input_count++;
   } else if (TryMatchImmediateOrShift(selector, &opcode, m.left().node(),
                                       &input_count, &inputs[1])) {
     if (!node->op()->HasProperty(Operator::kCommutative)) cont->Commute();
-    inputs[0] = g.UseRegister(m.right().node());
+    inputs[0] = g.UseRegisterOrStackPointer(m.right().node());
     input_count++;
   } else {
     opcode |= AddressingModeField::encode(kMode_Operand2_R);
-    inputs[input_count++] = g.UseRegister(m.left().node());
-    inputs[input_count++] = g.UseRegister(m.right().node());
+    inputs[input_count++] = g.UseRegisterOrStackPointer(m.left().node());
+    inputs[input_count++] = g.UseRegisterOrStackPointer(m.right().node());
   }
 
   if (has_result) {