Issue 57762 points out a compiler crash when the compiler was built
using a stock LLVM 7. LLVM 7 was released without a necessary fix for
a bug in the DWARF discriminant code.
This patch changes rustc to use the fallback mode on (non-Rust) LLVM 7.
Closes#57762
Fix emission of niche-filling discriminant values
Bug #55606 points out a regression introduced by #54004; namely that
an assertion can erroneously fire when a niche-filling discriminant
value is emitted.
This fixes the bug by removing the assertion, and furthermore by
arranging for the discriminant value to be masked according to the
size of the niche. This makes handling the discriminant a bit simpler
for debuggers.
The test case is from Jonathan Turner.
Closes#55606
Bug #55606 points out a regression introduced by #54004; namely that
an assertion can erroneously fire when a niche-filling discriminant
value is emitted.
This fixes the bug by removing the assertion, and furthermore by
arranging for the discriminant value to be masked according to the
size of the niche. This makes handling the discriminant a bit simpler
for debuggers.
The test case is from Jonathan Turner.
Closes#55606
Implement the rotate_left and rotate_right operations using
llvm.fshl and llvm.fshr if they are available (LLVM >= 7).
Originally I wanted to expose the funnel_shift_left and
funnel_shift_right intrinsics and implement rotate_left and
rotate_right on top of them. However, emulation of funnel
shifts requires emitting a conditional to check for zero shift
amount, which is not necessary for rotates. I was uncomfortable
doing that here, as I don't want to rely on LLVM to optimize
away that conditional (and for variable rotates, I'm not sure it
can). We should revisit that question when we raise our minimum
version requirement to LLVM 7 and don't need emulation code
anymore.
The DWARF generated for Rust enums was always somewhat unusual.
Rather than using DWARF constructs directly, it would emit magic field
names like "RUST$ENCODED$ENUM$0$Name" and "RUST$ENUM$DISR". Since
PR #45225, though, even this has not worked -- the ad hoc scheme was
not updated to handle the wider variety of niche-filling layout
optimizations now available.
This patch changes the generated DWARF to use the standard tags meant
for this purpose; namely, DW_TAG_variant and DW_TAG_variant_part.
The patch to implement this went in to LLVM 7. In order to work with
older versions of LLVM, and because LLVM doesn't do anything here for
PDB, the existing code is kept as a fallback mode.
Support for this DWARF is in the Rust lldb and in gdb 8.2.
Closes#32920Closes#32924Closes#52762Closes#53153
* Value gets renamed to Operand, so that now interpret::{Place, Operand} are the
"dynamic" versions of mir::{Place, Operand}.
* Operand and Place share the data for their "stuff is in memory"-base in a new
type, MemPlace. This also makes it possible to give some more precise types
in other areas. Both Operand and MemPlace have methods available to project
into fields (and other kinds of projections) without causing further
allocations.
* The type for "a Scalar or a ScalarPair" is called Value, and again used to
give some more precise types.
* All of these have versions with an attached layout, so that we can more often
drag the layout along instead of recomputing it. This lets us get rid of
`PlaceExtra::Downcast`. MPlaceTy and PlaceTy can only be constructed
in place.rs, making sure the layout is handled properly.
(The same should eventually be done for ValTy and OpTy.)
* All the high-level functions to write typed memory take a Place, and live in
place.rs. All the high-level typed functions to read typed memory take an
Operand, and live in operands.rs.
