Constant-fold !<number>

Constant-fold !<number>

The closure compiler reduces program size by replacing true with !0 and
false with !1.  Unfortunately, the code generated for !0 and !1 contains
unnecessary jumps and deoptimization support.

Constant folding directly improves code quality.

[Kasper Lund, 2011-06-10 09:20:08]

LGTM, but maybe it could be even better:

http://codereview.chromium.org/7044100/diff/1/src/parser.cc
File src/parser.cc (right):

http://codereview.chromium.org/7044100/diff/1/src/parser.cc#newcode2559
src/parser.cc:2559: if (value == 0) {
Could this be something ala:

   Handle<Object> boolean(isolate->heap()->ToBoolean(value == 0));
   return new(zone()) Literal(boolean);

or perhaps consider negating the result of calling
expression->AsLiteral()->handle()->ToBoolean() and refactoring the code so it
works for cases where the expression is a non-numeric literal.

[Kevin Millikin (Chromium), 2011-06-10 10:05:14]

http://codereview.chromium.org/7044100/diff/1/src/parser.cc
File src/parser.cc (right):

http://codereview.chromium.org/7044100/diff/1/src/parser.cc#newcode2559
src/parser.cc:2559: if (value == 0) {
On 2011/06/10 09:20:08, Kasper Lund wrote:
> Could this be something ala:
> 
>    Handle<Object> boolean(isolate->heap()->ToBoolean(value == 0));
>    return new(zone()) Literal(boolean);
> 
> or perhaps consider negating the result of calling
> expression->AsLiteral()->handle()->ToBoolean() and refactoring the code so it
> works for cases where the expression is a non-numeric literal.

We already have this constant folding in void
FullCodeGenerator::TestContext::Plug(Handle<Object> lit).  It just needs to be
'ported' to TestContext::BuildBranch(HValue* value) in hydrogen.cc.

I would prefer that solution rather than having it here, because it can properly
cope with things like

x = 0
if (!x) ...

[Kevin Millikin (Chromium), 2011-06-14 08:40:35]

http://codereview.chromium.org/7044100/diff/6001/src/parser.cc
File src/parser.cc (right):

http://codereview.chromium.org/7044100/diff/6001/src/parser.cc#newcode2559
src/parser.cc:2559: if (!isnan(value)) {
Does:

bool cond = isnan(value) || (value == 0);
Handle<Object> boolean(isolate()->heap()->ToBoolean(cond));

Handle the NaN case as well?

[Kevin Millikin (Chromium), 2011-09-15 09:47:05]

A modified version of this was landed a few months ago.  Closing the issue.