Issue 3807: Remove the ARM jump elimination.

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Issue 3807: Remove the ARM jump elimination. (Closed)

Created:
12 years, 2 months ago by Dean McNamee

Modified:
9 years, 7 months ago

Reviewers:
iposva, Kasper Lund

CC:
v8-dev

Visibility:
Public.

Description

Remove the ARM jump elimination. This completely removes jump elimination.

Patch Set 1 #

Patch Set 2 : Remove some comment additions to the x86 assembler. #

Patch Set 3 : Add back last_bound_pos_ and make a better comment. #

Patch Set 4 : Blah #

Created: 12 years, 2 months ago

Download [raw] [tar.bz2]

	Unified diffs	Side-by-side diffs	Delta from patch set	Stats (+7 lines, -72 lines)			Patch
M	src/assembler-arm.h	View		1 chunk	+1 line, -6 lines	0 comments	Download
M	src/assembler-arm.cc	View	1 2 3	4 chunks	+6 lines, -63 lines	0 comments	Download
M	src/flag-definitions.h	View		1 chunk	+0 lines, -3 lines	0 comments	Download

Messages

Total messages: 1 (0 generated)

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Dean McNamee

12 years, 2 months ago (2008-09-29 11:40:15 UTC) #1

From the little I now understand of ARM encoding, this optimization was never
possible on ARM.  The minimal forward branch that you can represent (zero in the
instruction field) will be 8 bytes forward, so you must branch over at least one
instruction.  This means "jump to next" is not possible on ARM, and therefor
this optimization was never possible.

I verified that indeed this code was never eliminating any jumps, and that we
are generating identical code before and after this change.

I am not at all familiar with the ARM code, so Ivan please look closely and make
sure I didn't do anything stupid.

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