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Crashing loads of uninitialized memory
proved to be a problem when implementing
unions using qbe. This patch introduces
a new UNDEF Ref to represent data that is
known to be uninitialized. Optimization
passes can make use of it to eliminate
some code. In the last compilation stages,
UNDEF is treated as the constant 0xdeaddead.
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The .val field is signed in RSlot.
Add a new dedicated function to
fetch it as a signed int.
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It is handy to express when
the end of a block cannot be
reached. If a hlt terminator
is executed, it traps the
program.
We don't go the llvm way and
specify execution semantics as
undefined behavior.
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Symbols are a useful abstraction
that occurs in both Con and Alias.
In this patch they get their own
struct. This new struct packages
a symbol name and a type; the type
tells us where the symbol name
must be interpreted (currently, in
gobal memory or in thread-local
storage).
The refactor fixed a bug in
addcon(), proving the value of
packaging symbol names with their
type.
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The apple targets are not done yet.
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Eg. data $a = { w $b $c }
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When qbe is used with other tools is a bit hard to identify
what is the tool that is generating the error. Adding an
identifier at the beginning of the line makes much easier
to identify the tool generating the error.
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Thanks to Daniel Xu for reporting.
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The risc-v abi needs to know if a
type is defined as a union or not.
We cannot use nunion to obtain this
information because the risc-v abi
made the unfortunate decision of
treating
union { int i; }
differently from
int i;
So, instead, I introduce a single
bit flag 'isunion'.
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This allows frontends to use BSS generically, without knowledge of
platform-dependent details.
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Necessary for floating-point negation, because
`%result = sub 0, %operand` doesn't give the correct sign for 0/-0.
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parseref() has code to reuse address constants, but this is not
done in other passes such as fold or isel. Introduce a new function
newcon() which takes a Con and returns a Ref for that constant, and
use this whenever creating address constants.
This is necessary to fix folding of address constants when one
operand is already folded. For example, in
%a =l add $x, 1
%b =l add %a, 2
%c =w loadw %b
%a and %b were folded to $x+1 and $x+3 respectively, but then the
second add is visited again since it uses %a. This gets folded to
$x+3 as well, but as a new distinct constant. This results in %b
getting labeled as bottom instead of either constant, disabling the
replacement of %b by a constant in subsequent instructions (such
as the loadw).
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Some abis, like the riscv one, treat
arguments differently depending on
whether they are variadic or not.
To prepare for the upcomming riscv
target, we change the variadic call
syntax and give meaning to the
location of the '...' marker.
# new syntax
%ret =w call $f(w %regular, ..., w %variadic)
By nature of their abis, the change
is backwards compatible for existing
targets.
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The documentation states that loadw is syntactic sugar for loadsw,
but it actually got parsed as Oload. If the result is an l temporary,
Oload behaves like Oloadl, not Oloadsw.
To fix this, parse Tloadw as Oloadsw explicitly.
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This was causing issues with aggregate types. A simple reproduction is:
type :type.1 = align 8 { 24 }
type :type.2 = align 8 { w 1, :type.1 1 }
The size of type.2 should be 32, adding only 4 bytes of padding between
the first and second field. Prior to this patch, 20 bytes of padding was
added instead, causing the type to have a size of 48.
Signed-off-by: Drew DeVault <sir@cmpwn.com>
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Reported by Alessandro Mantovani.
Overly long function names would
trigger out-of-bounds accesses.
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This allows you to explicitly specify the section to emit the data
directive for, allowing for sections other than .data: for example, .bss
or .init_array.
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This now only limits the number of arguments when parsing the input SSA,
which is usually a small fixed size (depending on the frontend).
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Compiler warned about comparison between signed and unsigned values.
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Symbols in the source file are still limited in
length because the rest of the code assumes that
strings always fit in NString bytes.
Regardless, there is already a benefit because
comparing/copying symbol names does not require
using strcmp()/strcpy() anymore.
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Since the environment can only be of type `l`, do
not require to write it down.
I also tightened the type information of the `pare`
and `arge` instructions.
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The arm64 ABI needs to know precisely what
floating point types are being used, so we
need to store that information.
I also made typ[] a dynamic array.
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This big diff does multiple changes to allow
the addition of new targets to qbe. The
changes are listed below in decreasing order
of impact.
1. Add a new Target structure.
To add support for a given target, one has to
implement all the members of the Target
structure. All the source files where changed
to use this interface where needed.
2. Single out amd64-specific code.
In this commit, the amd64 target T_amd64_sysv
is the only target available, it is implemented
in the amd64/ directory. All the non-static
items in this directory are prefixed with either
amd64_ or amd64_sysv (for items that are
specific to the System V ABI).
3. Centralize Ops information.
There is now a file 'ops.h' that must be used to
store all the available operations together with
their metadata. The various targets will only
select what they need; but it is beneficial that
there is only *one* place to change to add a new
instruction.
One good side effect of this change is that any
operation 'xyz' in the IL now as a corresponding
'Oxyz' in the code.
4. Misc fixes.
One notable change is that instruction selection
now generates generic comparison operations and
the lowering to the target's comparisons is done
in the emitter.
GAS directives for data are the same for many
targets, so data emission was extracted in a
file 'gas.c'.
5. Modularize the Makefile.
The Makefile now has a list of C files that
are target-independent (SRC), and one list
of C files per target. Each target can also
use its own 'all.h' header (for example to
define registers).
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The size of a union is the size of the largest
element aligned with the largest alignment.
For example, the size of the following union is
16, not 13 (as returned before this patch).
union {
char c[13];
int i;
};
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The spec says that numbers can be arbitrarily
big, and only the last 64 bits will be taken
into consideration. Calling sscanf does not
implement this, so I wrote an ad-hoc function.
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Compiling languages with closures often requires passing
an extra environment parameter to the called function.
One solution is to use a convention, and reserve, say,
the first argument for that purpose. However, that
makes binding to C a little less smooth.
Alternatively, QBE now provides a way to remain fully
ABI compatible with C by having a "hidden" environment
argument (marked with the keyword 'env'). Calling a
function expecting an environment from C will make the
contents of the environment undefined, but the normal
arguments will be passed without alteration. Conversely,
calling a C function like it is a closure by passing
it an environemnt will work smoothly.
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This change is backward compatible, calls to
"variadic" functions (like printf) must now be
annotated (with ...).
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