[turbofan] regalloc: avoid more redundant intersections

src/compiler/register-allocator.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/base/adapters.h"
 #include "src/compiler/linkage.h"
 #include "src/compiler/register-allocator.h"
 #include "src/string-stream.h"
 
 namespace v8 {
@@ skipping 2994 matching lines @@
         positions[aliased_reg] = LifetimePosition::GapFromInstructionIndex(0);
       }
     }
   }
 
   for (LiveRange* cur_inactive : inactive_live_ranges()) {
     DCHECK(cur_inactive->End() > range->Start());
     int cur_reg = cur_inactive->assigned_register();
     // No need to carry out intersections, when this register won't be
     // interesting to this range anyway.
-    if (positions[cur_reg] < range->Start()) continue;
+    // TODO(mtrofin): extend to aliased ranges, too.
+    if ((kSimpleFPAliasing || !check_fp_aliasing()) &&
+        positions[cur_reg] < range->Start()) {
+      continue;
+    }
 
     LifetimePosition next_intersection = cur_inactive->FirstIntersection(range);
     if (!next_intersection.IsValid()) continue;
     if (kSimpleFPAliasing || !check_fp_aliasing()) {
       positions[cur_reg] = Min(positions[cur_reg], next_intersection);
       TRACE("Register %s is free until pos %d (2)\n", RegisterName(cur_reg),
             Min(positions[cur_reg], next_intersection).value());
     } else {
       int alias_base_index = -1;
       int aliases = data()->config()->GetAliases(
@@ skipping 176 matching lines @@
         } else {
           use_pos[aliased_reg] =
               range->NextLifetimePositionRegisterIsBeneficial(current->Start());
         }
       }
     }
   }
 
   for (LiveRange* range : inactive_live_ranges()) {
     DCHECK(range->End() > current->Start());
+    int cur_reg = range->assigned_register();
+    bool is_fixed = range->TopLevel()->IsFixed();
+
+    // Don't perform costly intersections if they are guaranteed to not update
+    // block_pos or use_pos.
+    // TODO(mtrofin): extend to aliased ranges, too.
+    if ((kSimpleFPAliasing || !check_fp_aliasing()) && is_fixed) {
+      if (block_pos[cur_reg] < range->Start()) continue;
+    } else {
+      if (use_pos[cur_reg] < range->Start()) continue;
+    }
+
     LifetimePosition next_intersection = range->FirstIntersection(current);
     if (!next_intersection.IsValid()) continue;
-    int cur_reg = range->assigned_register();
-    bool is_fixed = range->TopLevel()->IsFixed();
+
     if (kSimpleFPAliasing || !check_fp_aliasing()) {
       if (is_fixed) {
         block_pos[cur_reg] = Min(block_pos[cur_reg], next_intersection);
         use_pos[cur_reg] = Min(block_pos[cur_reg], use_pos[cur_reg]);
       } else {
         use_pos[cur_reg] = Min(use_pos[cur_reg], next_intersection);
       }
     } else {
       int alias_base_index = -1;
       int aliases = data()->config()->GetAliases(
@@ skipping 757 matching lines @@
         }
       }
     }
   }
 }
 
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8