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Prepare LIR_ov to be used as soon Ed adds it and add a few comments that explain how overflow is handled.

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This commit is contained in:
Andreas Gal 2008-06-26 23:34:50 -08:00
parent 49fe7a95eb
commit a21ca6a788
3 changed files with 27 additions and 6 deletions
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30
js/src/jstracer.cpp
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@ -296,8 +296,13 @@ void
TraceRecorder::iinc(void* a, int incr, void* v, JSFrameRegs& regs)
{
LIns* ov = lir->ins2(LIR_add, get(a), lir->insImm(incr));
// SideExit exit;
// lir->insGuard(false, ov, regs);
// This check is actually supposed to happen in can_do_inc_dec, however,
// we arrive at iinc only if can_do_inc_dec passed, so we know that this
// guard must evaluate to false in the trace. We delay setting v to the
// result of the calculation until after the guard to make sure the
// result is not communicated to the interpreter in case this guard
// fails (as it was supposed to execute _before_ the add, not after.)
guard_ov(false, a, regs);
set(v, ov);
}
@ -309,20 +314,33 @@ TraceRecorder::snapshot(SideExit& exit, JSFrameRegs& regs)
return &exit;
}
#define G(ok) (ok ? LIR_xf : LIR_xt)
void
TraceRecorder::guard_0(bool ok, void* a, JSFrameRegs& regs)
{
SideExit exit;
lir->insGuard(G(ok), get(a), snapshot(exit, regs));
lir->insGuard(ok ? LIR_xf : LIR_xt,
get(a),
snapshot(exit, regs));
}
void
TraceRecorder::guard_h(bool ok, void* a, JSFrameRegs& regs)
{
SideExit exit;
lir->insGuard(G(ok), lir->ins1(LIR_callh, get(a)), snapshot(exit, regs));
lir->insGuard(ok ? LIR_xf : LIR_xt,
lir->ins1(LIR_callh, get(a)),
snapshot(exit, regs));
}
void
TraceRecorder::guard_ov(bool ok, void* a, JSFrameRegs& regs)
{
#if 0
SideExit exit;
lir->insGuard(ok ? LIR_xf : LIR_xt,
lir->ins1(LIR_ov, get(a)),
snapshot(exit, regs));
#endif
}
bool

1
js/src/jstracer.h
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@ -120,6 +120,7 @@ public:
void guard_0(bool ok, void* a, JSFrameRegs& regs);
void guard_h(bool ok, void* a, JSFrameRegs& regs);
void guard_ov(bool ok, void* a, JSFrameRegs& regs);
};
/*

2
js/src/jstracerinlines.h
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@ -520,6 +520,8 @@ static inline bool
guard_can_do_fast_inc_dec(JSContext* cx, JSFrameRegs& regs, jsval& v)
{
bool ok = interp_guard_can_do_fast_inc_dec(cx, regs, v);
// We have to check for overflow here, however we actually delay that
// until do_fast_inc_dec, where iinc will perform this check for us.
return ok;
}