On 2015/06/11 10:01:20, martyn.capewell wrote:
https://codereview.chromium.org/1179503003/diff/1/src/compiler/arm64/instruction-selector-arm64.cc
File src/compiler/arm64/instruction-selector-arm64.cc (right):
https://codereview.chromium.org/1179503003/diff/1/src/compiler/arm64/instruction-selector-arm64.cc#newcode749
src/compiler/arm64/instruction-selector-arm64.cc:749: if
(m.left().IsUint32MulHigh() && m.right().HasValue() &&
On 2015/06/11 04:25:52, Benedikt Meurer wrote:
> Can we limit the values on the right to [1,31] here? I.e. use
> m.right().IsInRange(1,31) instead?
I can, but I thought this operation was defined as only considering the
bottom
five bits of the shift operand, as in JS. The unit test provided tries to
check
this, too.
We also have a follow-up patch that resolves some of the semantics in this
area.
For example, we've seen shifts generated with shift operands > 31, where
the
operand is placed into a register for a register-controlled shift, which
isn't
necessary.
Well, I'd prefer to keep it simple on this level. Shift operands outside the
valid range is undefined behavior in C/C++ and I'd like to adhere to that
model
if possible. At least I'd be nice if we would not try to cover that with
optimizations.
https://codereview.chromium.org/1179503003/
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