[turbofan] Use correct block when tracing pending assessments in regalloc verifier

The verifier needs to use the block and assessments in that block corresponding to
a predecessor of a "pending" assessment. Not doing that causes incorrect
assessments when 2 locations are swapped.

BUG=665402

Review-Url: https://codereview.chromium.org/2515803002
Cr-Commit-Position: refs/heads/master@{#41159}

src/compiler/register-allocator-verifier.cc

@@ -469,7 +469,9 @@ void RegisterAllocatorVerifier::ValidateFinalAssessment(
   // is virtual_register.
   const PendingAssessment* old = assessment->original_pending_assessment();
   CHECK_NOT_NULL(old);
-  ValidatePendingAssessment(block_id, op, current_assessments, old,
+  RpoNumber old_block = old->origin()->rpo_number();
+  BlockAssessments* old_block_assessments = assessments_[old_block];
+  ValidatePendingAssessment(old_block, op, old_block_assessments, old,
                             virtual_register);
 }
 

test/mjsunit/regress/wasm/regression-665402.js

+// Copyright 2016 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.
+//
+// Flags: --expose-wasm
+
+load("test/mjsunit/wasm/wasm-constants.js");
+load("test/mjsunit/wasm/wasm-module-builder.js");
+
+var wire_bytes = readbuffer("test/mjsunit/regress/wasm/665402.wasm");
+var module = new WebAssembly.Module(wire_bytes);
+assertTrue(module != undefined);