1185739 - Fix self-comparison warnings in MemoryMetrics.h

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Jeff Walden [:Waldo]]

The Servo stuff in MemoryMetrics.h added a self-comparison -- that is, ServoSizes::Foo == ServoSizes::Foo for some enum initializer Foo.  This triggers compiler self-comparison warnings up the wazoo with my clang.

Comment 1

[Jeff Walden [:Waldo]]

Attachment: Patch

https://hg.mozilla.org/integration/mozilla-inbound/rev/d8f5d0f09eec was the initial introduction of the warning.  Key is in the macro, ServoSizes::servoKind is ServoSizes::GCHeapUsed, ServoSizes::MallocHeap, ServoSizes::NonHeap and so on from the FOR_EACH_SIZE macro, and comparing against ServoSizes::GCHeapUsed is a self-comparison.  Work around this by doing a same-type check using the enum values (all >= 0) as array lengths.  A bit arcane, but the comment explains why, at least.

Comment 2

[Eric Faust [:efaust]]

Comment on attachment 8636261 [details] [diff] [review]
Patch

Review of attachment 8636261 [details] [diff] [review]:
-----------------------------------------------------------------

APPROVED.

::: js/public/MemoryMetrics.h
@@ +148,3 @@
>  #define ADD_SIZE_TO_N(tabKind, servoKind, mSize)                  n += mSize;
> +#define ADD_SIZE_TO_N_IF_LIVE_GC_THING(tabKind, servoKind, mSize) \
> +    /* Avoid self-comparison warnings by compare enums indirectly. */ \

nit: by comparing

Comment 3

[Pulsebot]

https://hg.mozilla.org/integration/mozilla-inbound/rev/14b93413d8b8

Comment 4

[Nicolas B. Pierron [:nbp]]

FYI, I have a patch locally which works by subtracting them and comparing against 0, instead of doing an equality test.

Comment 5

[Carsten Book [:Tomcat]]

https://hg.mozilla.org/mozilla-central/rev/14b93413d8b8