The change is made since for switch statements with lots of cases,
where each case is a constant integer, the emitted bytecode is still
a series of jumps, when we can instead use a jump table.
If there are 6 or more cases (similar to GCC) of Smi literals, and
if the max Smi case minus the min Smi case is not more than 3 times
the number of cases, we use a jump table up front to handle Smi's,
and then use traditional if-else logic for the rest of the cases.
We then use the jump table in interpreter/bytecode-jump-table to
do the optimization.
This tries to go off issue 9738 in v8's issue tracker. It is not
exactly the same, since that recommends doing the work at JIT-time,
but has similar ideas. It also partially goes off issue 10764.
Bug: v8:9738
Change-Id: Ic805682ee3abf9ce464bb733b427fa0c83a6e10c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2904926
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75323}
This is a reland of 35269f77f8
Switches on an expression that unconditionally throws would have all their
case statements dead, causing a DCHECK error in the SwitchBuilder. This
fixes up the DCHECK to allow dead labels.
Original change's description:
> [ignition] Skip binding dead labels
>
> BytecodeLabels for forward jumps may create a dead basic block if their
> corresponding jump was elided (due to it dead code elimination). We can
> avoid generating such dead basic blocks by skipping the label bind when
> no corresponding jump has been observed. This works because all jumps
> except JumpLoop are forward jumps, so we only have to special case one
> Bind for loop headers to bind unconditionally.
>
> Since Binds are now conditional on a jump existing, we can no longer rely
> on using Bind to get the current offset (e.g. at the beginning of a try
> block). Instead, we now expose the current offset in the bytecode array
> writer. Conveniently, this means that we can be a bit smarter about basic
> blocks around these statements.
>
> As a drive-by, remove the unused Bind(target,label) function.
>
> Bug: chromium:934166
> Change-Id: I532aa452fb083560d07b90da99caca0b1d082aa3
> Reviewed-on: https://chromium-review.googlesource.com/c/1488763
> Commit-Queue: Leszek Swirski <leszeks@chromium.org>
> Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#59942}
TBR=rmcilroy@chromium.org
Bug: chromium:934166
Change-Id: If6eab4162106717ce64a2dc477000c6a76354cb4
Reviewed-on: https://chromium-review.googlesource.com/c/1494535
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59948}
The ES2015 specification for switch statements 13.12.11 specifies that
they get their own lexical scope. This patch introduces such a scope
through a complex desugaring in terms of blocks, done so that Crankshaft
does not have to be updated to support multiple constructs providing
scopes.
Recommitting this patch after a bug fix in Crankshaft to allow a
desugaring with certain elements missing a source location:
https://codereview.chromium.org/1313443002
BUG=v8:4377
LOG=Y
R=adamk
Review URL: https://codereview.chromium.org/1309163003
Cr-Commit-Position: refs/heads/master@{#30340}
Reason for revert:
Breaks cctest/test-cpu-profiler/SourceLocation on nosnap
Original issue's description:
> Add a separate scope for switch
>
> The ES2015 specification for switch statements 13.12.11 specifies that
> they get their own lexical scope. This patch introduces such a scope
> through a complex desugaring in terms of blocks, done so that Crankshaft
> does not have to be updated to support multiple constructs providing
> scopes.
>
> BUG=v8:4377
> LOG=Y
> R=adamk
>
> Committed: https://crrev.com/9edbc1f21eb1050cabbe3b8bc9aebf89ada7ebd7
> Cr-Commit-Position: refs/heads/master@{#30314}
TBR=adamk@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=v8:4377
Review URL: https://codereview.chromium.org/1309043004
Cr-Commit-Position: refs/heads/master@{#30316}
The ES2015 specification for switch statements 13.12.11 specifies that
they get their own lexical scope. This patch introduces such a scope
through a complex desugaring in terms of blocks, done so that Crankshaft
does not have to be updated to support multiple constructs providing
scopes.
BUG=v8:4377
LOG=Y
R=adamk
Review URL: https://codereview.chromium.org/1293283002
Cr-Commit-Position: refs/heads/master@{#30314}
