commit 79e6eb8b79be6249358b7801bc511290dacf10d0
author Mathieu Chartier <mathieuc@google.com> Mon Aug 26 12:33:46 2019 -0700
committer Mathieu Chartier <mathieuc@google.com> Thu Aug 29 16:05:52 2019 +0000
tree 1a04d214dd6223423abd442d8d9b0b61a3db2336
parent bae88c0759d48acf29b58d960ad2665e3462dfda

Prevent overflow for AOT hotness counters

Previous, the addition did not have a check for overflow and might wrap
around since the counter is only 16 bits.

Modified the test to exercise this.

The slowdown from fixing the overflow is 2% average on golem arm32/64.
Overall this brings the slowdown from the counter to ~15% from ~13%.

The benchmarks that regress the most are loopy ones that I would
consider non-representative. Code size increases by 0.6%.

Bug: 139883463
Test: test/run-test --host --64 --prebuild 674-hotness-compiled
Test: test/run-test --host --prebuild 674-hotness-compiled
Test: test/run-test --64 --prebuild 674-hotness-compiled
Test: test/run-test ---prebuild 674-hotness-compiled

Change-Id: Icf0ab2aedbc40ab10c9d952ce0f9c7b5e5feaf15

compiler/optimizing/code_generator_x86.cc

diff --git a/compiler/optimizing/code_generator_x86.cc b/compiler/optimizing/code_generator_x86.cc
index 4ab398e..797fe32 100644
--- a/compiler/optimizing/code_generator_x86.cc
+++ b/compiler/optimizing/code_generator_x86.cc
@@ -1078,8 +1078,15 @@
   DCHECK(GetCompilerOptions().GetImplicitStackOverflowChecks());
 
   if (GetCompilerOptions().CountHotnessInCompiledCode()) {
-    __ addw(Address(kMethodRegisterArgument, ArtMethod::HotnessCountOffset().Int32Value()),
+    NearLabel overflow;
+    __ cmpw(Address(kMethodRegisterArgument,
+                    ArtMethod::HotnessCountOffset().Int32Value()),
+            Immediate(ArtMethod::MaxCounter()));
+    __ j(kEqual, &overflow);
+    __ addw(Address(kMethodRegisterArgument,
+                    ArtMethod::HotnessCountOffset().Int32Value()),
             Immediate(1));
+    __ Bind(&overflow);
   }
 
   if (!skip_overflow_check) {
@@ -1385,7 +1392,13 @@
     if (codegen_->GetCompilerOptions().CountHotnessInCompiledCode()) {
       __ pushl(EAX);
       __ movl(EAX, Address(ESP, kX86WordSize));
-      __ addw(Address(EAX, ArtMethod::HotnessCountOffset().Int32Value()), Immediate(1));
+          NearLabel overflow;
+      __ cmpw(Address(EAX, ArtMethod::HotnessCountOffset().Int32Value()),
+              Immediate(ArtMethod::MaxCounter()));
+      __ j(kEqual, &overflow);
+      __ addw(Address(EAX, ArtMethod::HotnessCountOffset().Int32Value()),
+              Immediate(1));
+      __ Bind(&overflow);
       __ popl(EAX);
     }
     GenerateSuspendCheck(info->GetSuspendCheck(), successor);