[lldb] Fix type conversion in the Scalar getters

Authored by labath on Jun 29 2020, 7:17 AM.


[lldb] Fix type conversion in the Scalar getters

The Scalar class claims to follow the C type conversion rules. This is
true for the Promote function, but it is not true for the implicit
conversions done in the getter methods.

These functions had a subtle bug: when extending the type, they used the
signedness of the *target* type in order to determine whether to do
sign-extension or zero-extension. This is not how things work in C,
which uses the signedness of the *source* type. I.e., C does
(sign-)extension before it does signed->unsigned conversion, and not the
other way around.

This means that: (unsigned long)(int)-1

is equal to (unsigned long)0xffffffffffffffff
and not (unsigned long)0x00000000ffffffff

Unsurprisingly, we have accumulated code which depended on this
inconsistent behavior. It mainly manifested itself as code calling
"ULongLong/SLongLong" as a way to get the value of the Scalar object in
a primitive type that is "large enough". Previously, the ULongLong
conversion did not do sign-extension, but now it does.

This patch makes the Scalar getters consistent with the declared
semantics, and fixes the couple of call sites that were using it

Reviewers: teemperor, JDevlieghere

Subscribers: lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D82772


labathJul 2 2020, 9:02 AM
Differential Revision
D82772: [lldb] Fix type conversion in the Scalar getters
rG8b7b0ad24c73: [AArch64][SVE] NFC: Rename isOrig -> isReverseInstr