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Issue
169893002:
A64: Let the MacroAssembler resolve branches to distant targets. (Closed)
DescriptionA64: Let the MacroAssembler resolve branches to distant targets.
Code generation would fail when assembling a branch to a label that is bound
outside the immediate range of the instruction. A64 is sensitive to this, as the
various branching instructions have different ranges, going down to +-32KB for
TBZ/TBNZ. The MacroAssembler is augmented to handle branches to targets that
may exceed the immediate range of instructions.
When branching backward to a label exceeding the instruction range, the
MacroAssembler can simply tweak the generated code to use an unconditional
branch with a longer range. For example instead of
B(cond, &label);
the MacroAssembler can generate:
b(InvertCondition(cond), &done);
b(&label);
bind(&done);
Since the target is not known when the branch is emitted, forward branches uses
a different mechanism. The MacroAssembler keeps track of forward branches to
unbound labels. When the code generation approaches the end of the range of a
branch, a veneer is generated for the branch.
BUG=v8:3148
LOG=Y
R=ulan@chromium.org
Committed: https://code.google.com/p/v8/source/detail?r=19444
Patch Set 1 #
Total comments: 8
Patch Set 2 : Addressed Ulan's comments. #
Total comments: 1
Messages
Total messages: 7 (0 generated)
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