From a09025460631dc60477bbcd9f59e04673d8cce4c Mon Sep 17 00:00:00 2001
From: Vladimir Marko <vmarko@google.com>
Date: Tue, 13 Feb 2024 08:11:47 +0000
Subject: Unresolved field access HIR are not schedulable.

Add a comment and remove dead code.

Test: m test-art-host-gtest
Test: testrunner.py --host --optimizing
Change-Id: Ie14a1bd9633f322be7cb4bb312a1232df6697cbd
---
 compiler/optimizing/scheduler.cc | 43 ++++++++++++----------------------------
 1 file changed, 13 insertions(+), 30 deletions(-)

(limited to 'compiler/optimizing/scheduler.cc')

diff --git a/compiler/optimizing/scheduler.cc b/compiler/optimizing/scheduler.cc
index 9b5091a81a..4236a545bc 100644
--- a/compiler/optimizing/scheduler.cc
+++ b/compiler/optimizing/scheduler.cc
@@ -106,35 +106,15 @@ static bool IsArrayAccess(const HInstruction* instruction) {
 }
 
 static bool IsInstanceFieldAccess(const HInstruction* instruction) {
-  return instruction->IsInstanceFieldGet() ||
-         instruction->IsInstanceFieldSet() ||
-         instruction->IsUnresolvedInstanceFieldGet() ||
-         instruction->IsUnresolvedInstanceFieldSet();
+  return instruction->IsInstanceFieldGet() || instruction->IsInstanceFieldSet();
 }
 
 static bool IsStaticFieldAccess(const HInstruction* instruction) {
-  return instruction->IsStaticFieldGet() ||
-         instruction->IsStaticFieldSet() ||
-         instruction->IsUnresolvedStaticFieldGet() ||
-         instruction->IsUnresolvedStaticFieldSet();
-}
-
-static bool IsResolvedFieldAccess(const HInstruction* instruction) {
-  return instruction->IsInstanceFieldGet() ||
-         instruction->IsInstanceFieldSet() ||
-         instruction->IsStaticFieldGet() ||
-         instruction->IsStaticFieldSet();
-}
-
-static bool IsUnresolvedFieldAccess(const HInstruction* instruction) {
-  return instruction->IsUnresolvedInstanceFieldGet() ||
-         instruction->IsUnresolvedInstanceFieldSet() ||
-         instruction->IsUnresolvedStaticFieldGet() ||
-         instruction->IsUnresolvedStaticFieldSet();
+  return instruction->IsStaticFieldGet() || instruction->IsStaticFieldSet();
 }
 
 static bool IsFieldAccess(const HInstruction* instruction) {
-  return IsResolvedFieldAccess(instruction) || IsUnresolvedFieldAccess(instruction);
+  return IsInstanceFieldAccess(instruction) || IsStaticFieldAccess(instruction);
 }
 
 static const FieldInfo* GetFieldInfo(const HInstruction* instruction) {
@@ -165,12 +145,6 @@ bool SideEffectDependencyAnalysis::MemoryDependencyAnalysis::FieldAccessMayAlias
     return false;
   }
 
-  // If either of the field accesses is unresolved.
-  if (IsUnresolvedFieldAccess(instr1) || IsUnresolvedFieldAccess(instr2)) {
-    // Conservatively treat these two accesses may alias.
-    return true;
-  }
-
   // If both fields accesses are resolved.
   size_t instr1_field_access_heap_loc = FieldAccessHeapLocation(instr1);
   size_t instr2_field_access_heap_loc = FieldAccessHeapLocation(instr2);
@@ -201,6 +175,14 @@ bool SideEffectDependencyAnalysis::MemoryDependencyAnalysis::HasMemoryDependency
     return true;
   }
 
+  // Note: Unresolved field access instructions are currently marked as not schedulable.
+  // If we change that, we should still keep in mind that these instructions can throw and
+  // read or write volatile fields and, if static, cause class initialization and write to
+  // arbitrary heap locations, and therefore cannot be reordered with any other field or
+  // array access to preserve the observable behavior. The only exception is access to
+  // singleton members that could actually be reodered across these instructions but we
+  // currently do not analyze singletons here anyway.
+
   if (IsArrayAccess(instr1) && IsArrayAccess(instr2)) {
     return ArrayAccessMayAlias(instr1, instr2);
   }
@@ -717,7 +699,8 @@ bool HScheduler::IsSchedulable(const HInstruction* instruction) const {
   //    HNop
   //    HThrow
   //    HTryBoundary
-  //    All volatile field access e.g. HInstanceFieldGet
+  //    All unresolved field access instructions
+  //    All volatile field access instructions, e.g. HInstanceFieldGet
   // TODO: Some of the instructions above may be safe to schedule (maybe as
   // scheduling barriers).
   return instruction->IsArrayGet() ||
-- 
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