The GNU assembler supports prefixing the expression with a '#' to indiciate that
the value that is being moved is infact a constant. This improves the
compatibility of the integrated assembler's parser for this.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198916 91177308-0d34-0410-b5e6-96231b3b80d8
The GNU assembler has an extension that allows for the elision of the paired
register (dt2) for the LDRD and STRD mnemonics. Add support for this in the
assembly parser. Canonicalise the usage during the instruction parsing from
the specified version.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198915 91177308-0d34-0410-b5e6-96231b3b80d8
The ARM ARM indicates the mnemonics as follows:
ldrbt{<c>}{<q>} <Rt>, [<Rn>], {, #+/-<imm>}
ldrt{<c>}{<q>} <Rt>, [<Rn>] {, #+/-<imm>}
strbt{<c>}{<q>} <Rt>, [<Rn>] {, #<imm>}
strt{<c>}{<q>} <Rt>, [<Rn>] {, #+/-<imm>}
This improves the parser to deal with the implicit immediate 0 for the mnemonics
as per the specification.
Thanks to Joerg Sonnenberger for the tests!
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198914 91177308-0d34-0410-b5e6-96231b3b80d8
This reverts commit r198865 which reverts r198851.
ASan identified a use-of-uninitialized of the DwarfTypeUnit::Ty variable
in skeleton type units.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198908 91177308-0d34-0410-b5e6-96231b3b80d8
The zext handling added in r197802 wasn't right for RNSBG. This patch
restricts it to ROSBG, RXSBG and RISBG. (The tests for RISBG were added
in r197802 since RISBG was the motivating example.)
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198862 91177308-0d34-0410-b5e6-96231b3b80d8
At the moment we expect rotates to have the form:
(or (shl X, Y), (shr X, Z))
where Y == bitsize(X) - Z or Z == bitsize(X) - Y. This form means that
the (or ...) is undefined for Y == 0 or Z == 0. This undefinedness can
be avoided by using Y == (C * bitsize(X) - Z) & (bitsize(X) - 1) or
Z == (C * bitsize(X) - Y) & (bitsize(X) - 1) for any integer C
(including 0, the most natural choice).
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198861 91177308-0d34-0410-b5e6-96231b3b80d8
InstCombine converts (sub 32, (add X, C)) into (sub 32-C, X),
so a rotate left of a 32-bit Y by X+C could appear as either:
(or (shl Y, (add X, C)), (shr Y, (sub 32, (add X, C))))
without InstCombine or:
(or (shl Y, (add X, C)), (shr Y, (sub 32-C, X)))
with it.
We already matched the first form. This patch handles the second too.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198860 91177308-0d34-0410-b5e6-96231b3b80d8
root path to which object files managed by the LLIObjectCache instance should be
written. This option defaults to "", in which case objects are cached in the
same directory as the bitcode they are derived from.
The load-object-a.ll test has been rewritten to use this option to support
testing in environments where the test directory is not writable.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198852 91177308-0d34-0410-b5e6-96231b3b80d8
Rename bytecode to opcodes to make it more clear. Change an impossible case to
llvm_unreachable instead. Avoid allocation of a buffer by modifying the
PrintOpcodes iteration.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198848 91177308-0d34-0410-b5e6-96231b3b80d8
In the stackmap format we advertise the constant field as signed.
However, we were determining whether to promote to a 64-bit constant
pool based on an unsigned comparison.
This fix allows -1 to be encoded as a small constant.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198816 91177308-0d34-0410-b5e6-96231b3b80d8
This makes it easier to write a test that's mostly shared between
fission and non-fission (using FileCheck's multiple prefix support).
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198806 91177308-0d34-0410-b5e6-96231b3b80d8
MIsNeedChainEdge, which is used by -enable-aa-sched-mi (AA in misched), had an
llvm_unreachable when -enable-aa-sched-mi is enabled and we reach an
instruction with multiple MMOs. Instead, return a conservative answer. This
allows testing -enable-aa-sched-mi on x86.
Also, this moves the check above the isUnsafeMemoryObject checks.
isUnsafeMemoryObject is currently correct only for instructions with one MMO
(as noted in the comment in isUnsafeMemoryObject):
// We purposefully do no check for hasOneMemOperand() here
// in hope to trigger an assert downstream in order to
// finish implementation.
The problem with this is that, had the candidate edge passed the
"!MIa->mayStore() && !MIb->mayStore()" check, the hoped-for assert would never
happen (which could, in theory, lead to incorrect behavior if one of these
secondary MMOs was volatile, for example).
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198795 91177308-0d34-0410-b5e6-96231b3b80d8
to the following two rules:
1) fold (vselect (build_vector AllOnes), A, B) -> A
2) fold (vselect (build_vector AllZeros), A, B) -> B
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198777 91177308-0d34-0410-b5e6-96231b3b80d8
They do *different* things to %esp, so they are not equivalent.
Rename PUSHi8 to PUSH32i8 and add the missing PUSH16i8.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198761 91177308-0d34-0410-b5e6-96231b3b80d8
We can't do a perfect job here. We *have* to allow (%dx) even in 64-bit
mode, for example, because it might be used for an unofficial form of
the in/out instructions. We actually want to do a better job of validation
*later*. Perhaps *instead* of doing it where we are at the moment.
But for now, doing what validation we *can* do in the place that the code
already has its validation, is an improvement.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198760 91177308-0d34-0410-b5e6-96231b3b80d8
It seems there is no separate instruction class for having AdSize *and*
OpSize bits set, which is required in order to disambiguate between all
these instructions. So add that to the disassembler.
Hm, perhaps we do need an AdSize16 bit after all?
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198759 91177308-0d34-0410-b5e6-96231b3b80d8
Where "where possible" means that it's an immediate value and it's below
0x10000. In fact GAS will either truncate or error with larger values,
and will insist on using the addr32 prefix to get 32-bit addressing. So
perhaps we should do that, in a later patch.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198758 91177308-0d34-0410-b5e6-96231b3b80d8
JCXZ should have the 0x67 prefix only if we're in 32-bit mode, so make that
appropriately conditional. And JECXZ needs the prefix instead.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198757 91177308-0d34-0410-b5e6-96231b3b80d8
I couldn't see how to do this sanely without splitting RETQ from RETL.
Eric says: "sad about the inability to roundtrip them now, but...".
I have no idea what that means, but perhaps it wants preserving in the
commit comment.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198756 91177308-0d34-0410-b5e6-96231b3b80d8
This fixes the bulk of 16-bit output, and the corresponding test case
x86-16.s now looks mostly like the x86-32.s test case that it was
originally based on. A few irrelevant instructions have been dropped,
and there are still some corner cases to be fixed in subsequent patches.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198752 91177308-0d34-0410-b5e6-96231b3b80d8
Modern versions of OSX/Darwin's ld (ld64 > 97.17) have an optimisation present that allows the back end to omit relocations (and replace them with an absolute difference) for FDE some text section refs.
This patch allows a backend to opt-in to this behaviour by setting "DwarfFDESymbolsUseAbsDiff". At present, this is only enabled for modern x86 OSX ports.
test changes by David Fang.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198744 91177308-0d34-0410-b5e6-96231b3b80d8
Appease the buildbots for targets which do not build the ARM support by moving
the ARM specific test into a subdirectory and use the lit configuration to
disable them appropriately.
Thanks to chapuni and thakis for explaining how to do this!
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198736 91177308-0d34-0410-b5e6-96231b3b80d8
Operands which involved label arithemetic would previously fail to parse. This
corrects that by adding the additional case for the shift operand validation.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198735 91177308-0d34-0410-b5e6-96231b3b80d8
This adds some preliminary support for decoding ARM EHABI unwinding information.
The major functionality that remains from complete support is bytecode
translation.
Each Unwind Index Table is printed out as a separate entity along with its
section index, name, offset, and entries.
Each entry lists the function address, and if possible, the name, of the
function to which it corresponds. The encoding model, personality routine or
index, and byte code is also listed.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198734 91177308-0d34-0410-b5e6-96231b3b80d8
take type from the new symbol but merge them so that the type
is never "downgraded".
This is probably quite rare, except for IFUNC symbols which
we used to misassemble, losing the IFUNC type.
Fixes#18372.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198706 91177308-0d34-0410-b5e6-96231b3b80d8
With the gnu objc runtime private strings are used. Since we only need to
produce a unique label, the fix is to just drop the asserts.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198701 91177308-0d34-0410-b5e6-96231b3b80d8
This commit adds the pre-UAL aliases of fconsts and fconstd for
vmov.f32 and vmov.f64. They use an InstAlias rather than a
MnemonicAlias to properly support the predicate operand.
We need to support encoded 8-bit constants in order to implement the
pre-UAL fconsts/fconstd aliases for vmov.f32/vmov.f64, so this
commit also fixes parsing of encoded floating point constants used
in vmov.f32/vmov.f64 instructions. Now we can support assembly code
like this:
fconsts s0, #0x70
which is equivalent to vmov.f32 s0, #1.0.
Most of the code was already in place to support this feature.
Previously the code was trying to accept encoded 8-bit float
constants for the vmov.f32/vmov.f64 instructions. It looks like the
support for parsing encoded floats was lost in a refactoring in
commit r148556 and we did not have any tests in place to catch it.
The change in this commit is to keep the parsed value as a 32-bit
float instead of a 64-bit double because that is what the isFPImm()
function expects to find. There is no loss of precision by using a
32-bit float here because we are still limited to an 8-bit encoded
value in the end.
Additionally, we explicitly reject encoded 8-bit floats for
vmovf.32/64. This is the same as the current behavior, but we now do
it explicitly rather than accidently.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198697 91177308-0d34-0410-b5e6-96231b3b80d8
This doesn't seem to have actually broken anything. It was paranoia
on my part. Trying again now that bots are more stable.
This is a follow up of the r198338 commit that added truncates for
lcssa phi nodes. Sinking the truncates below the phis cleans up the
loop and simplifies subsequent analysis within the indvars pass.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198678 91177308-0d34-0410-b5e6-96231b3b80d8
Switch the context to be SmallVectors. This allows for saving additional
context when providing previous emission sites.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198665 91177308-0d34-0410-b5e6-96231b3b80d8
Move the unwinding context for the ARM IAS into a helper class. This is purely
a structural refactoring. A follow up change allows for recording additional
depth to improve diagnostics.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198664 91177308-0d34-0410-b5e6-96231b3b80d8
Parse tag names as well as expressions. The former is part of the
specification, the latter is for improved compatibility with the GNU assembler.
Fix attribute value handling to be comformant to the specification.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198662 91177308-0d34-0410-b5e6-96231b3b80d8
Introduce a new virtual method Note into the AsmParser. This completements the
existing Warning and Error methods. Use the new method to clean up the output
of the unwind routines in the ARM AsmParser.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198661 91177308-0d34-0410-b5e6-96231b3b80d8
This is a follow up of the r198338 commit that added truncates for
lcssa phi nodes. Sinking the truncates below the phis cleans up the
loop and simplifies subsequent analysis within the indvars pass.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198654 91177308-0d34-0410-b5e6-96231b3b80d8
This patch adds .abicalls and .set pic0 support which
affects the ELF ABI and its flags. In addition the patch uses
a common interface for both the MipsTargetSteamer and
MipsObjectStreamer that both the integrated and standalone
assemblers will use for the output for these directives.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198646 91177308-0d34-0410-b5e6-96231b3b80d8
Now with a fix for PR18384: ValueHandleBase::ValueIsDeleted.
We need to invalidate SCEV's loop info when we delete a block, even if no values are hoisted.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198631 91177308-0d34-0410-b5e6-96231b3b80d8
The ARM backend has been using most of the MachO related subtarget
checks almost interchangeably, and since the only target it's had to
run on has been IOS (which is all three of MachO, Darwin and IOS) it's
worked out OK so far.
But we'd like to support embedded targets under the "*-*-none-macho"
triple, which means everything starts falling apart and inconsistent
behaviours emerge.
This patch should pick a reasonably sensible set of behaviours for the
new triple (and any others that come along, with luck). Some choices
were debatable (notably FP == r7 or r11), but we can revisit those
later when deficiencies become apparent.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198617 91177308-0d34-0410-b5e6-96231b3b80d8
This requires a knowledge of the stack size which is not known until
the frame is complete, hence the need for the XCoreFTAOElim pass
which lowers the XCoreISD::FRAME_TO_ARGS_OFFSET instrution into its
final form.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198614 91177308-0d34-0410-b5e6-96231b3b80d8
Longer term, we want to move users to "*-*-*-macho" for embedded work, but for
now people are relying on the last thing we told them, which is unfortunately
"*-*-darwin-eabi".
rdar://problem/15703934
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198602 91177308-0d34-0410-b5e6-96231b3b80d8
The 0x66 prefix toggles between 16-bit and 32-bit addressing mode.
So in 32-bit mode it is used to switch to 16-bit addressing mode for the
following instruction, while in 16-bit mode it's the other way round — it's
used to switch to 32-bit mode instead.
Thus, emit the 0x66 prefix byte for OpSize only in 32-bit (and 64-bit) mode,
and introduce a new OpSize16 bit which is used in 16-bit mode instead.
This is just the basic infrastructure for that change; a subsequent patch
will add the new OpSize16 bit to the 32-bit instructions that need it.
Patch from David Woodhouse.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198586 91177308-0d34-0410-b5e6-96231b3b80d8
This is not really expected to work right yet. Mostly because we will
still emit the OpSize (0x66) prefix in all the wrong places, along with
a number of other corner cases. Those will all be fixed in the subsequent
commits.
Patch from David Woodhouse.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198584 91177308-0d34-0410-b5e6-96231b3b80d8
There is a wrong assumption that the vector element type and the
type of each ConstantSDNode in the build_vector were the same.
However, when promoting the integer operand of a legally typed
build_vector, the operand type and the vector element type do not
need to be the same
(See method 'DAGTypeLegalizer::PromoteIntOp_BUILD_VECTOR' in
LegalizeIntegerTypes.cpp).
in AArch64 backend, the following dag sequence:
C0: i1 = Constant<0>
C1: i1 = Constant<-1>
V: v8i1 = BUILD_VECTOR C1, C1, C0, C0, C0, C0, C0, C0
is type-legalized into:
NewC0: i32 = Constant<0>
NewC1: i32 = Constant<1>
V: v8i8 = BUILD_VECTOR NewC1, NewC1, NewC0, NewC0, NewC0, NewC0, NewC0, NewC0
Forcing a getZeroExtend to VTBits to ensure that the new constant
is correctly.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198582 91177308-0d34-0410-b5e6-96231b3b80d8
Add some tests to validate correct register selection, including a fix
to an existing test which was requiring the *wrong* output.
Patch from David Woodhouse.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198566 91177308-0d34-0410-b5e6-96231b3b80d8
Removed vzeroupper from AVX-512 mode - our optimization gude does not recommend to insert vzeroupper at all.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198557 91177308-0d34-0410-b5e6-96231b3b80d8
__builtin_returnaddress requires that the value passed into is be a constant.
However, at -O0 even a constant expression may not be converted to a constant.
Emit an error message intead of crashing.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198531 91177308-0d34-0410-b5e6-96231b3b80d8
This commit was the source of crasher PR18384:
While deleting: label %for.cond127
An asserting value handle still pointed to this value!
UNREACHABLE executed at llvm/lib/IR/Value.cpp:671!
Reverting to get the builders green, feel free to re-land after fixing up.
(Renato has a handy isolated repro if you need it.)
This reverts commit r198478.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198503 91177308-0d34-0410-b5e6-96231b3b80d8
getSCEV for an ashr instruction creates an intermediate zext
expression when it truncates its operand.
The operand is initially inside the loop, so the narrow zext
expression has a non-loop-invariant loop disposition.
LoopSimplify then runs on an outer loop, hoists the ashr operand, and
properly invalidate the SCEVs that are mapped to value.
The SCEV expression for the ashr is now an AddRec with the hoisted
value as the now loop-invariant start value.
The LoopDisposition of this wide value was properly invalidated during
LoopSimplify.
However, if we later get the ashr SCEV again, we again try to create
the intermediate zext expression. We get the same SCEV that we did
earlier, and it is still cached because it was never mapped to a
Value. When we try to create a new AddRec we abort because we're using
the old non-loop-invariant LoopDisposition.
I don't have a solution for this other than to clear LoopDisposition
when LoopSimplify hoists things.
I think the long-term strategy should be to perform LoopSimplify on
all loops before computing SCEV and before running any loop opts on
individual loops. It's possible we may want to rerun LoopSimplify on
individual loops, but it should rarely do anything, so rarely require
invalidating SCEV.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198478 91177308-0d34-0410-b5e6-96231b3b80d8
This reverts commit r198398, thus reapplying r198397.
I had accidentally introduced an endianness issue when applying the hash
to the type unit. Using support::ulittle64_t in the reinterpret_cast in
addDwarfTypeUnitType fixes this issue.
Original commit message:
Debug Info: Type Units: Simplify type hashing using IR-provided unique
names.
What's good for LTO metadata size problems ought to be good for non-LTO
debug info size too, so let's rely on the same uniqueness in both cases.
If it's insufficient for non-LTO for whatever reason (since we now won't
be uniquing CU-local types or any C types - but these are likely to not
be the most significant contributors to type bloat) we should consider a
frontend solution that'll help both LTO and non-LTO alike, rather than
using DWARF-level DIE-hashing that only helps non-LTO debug info size.
It's also much simpler this way and benefits C++ even more since we can
deduplicate lexically separate definitions of the same C++ type since
they have the same mangled name.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198436 91177308-0d34-0410-b5e6-96231b3b80d8
The loop rerolling pass was failing with an assertion failure from a
failed cast on loops like this:
void foo(int *A, int *B, int m, int n) {
for (int i = m; i < n; i+=4) {
A[i+0] = B[i+0] * 4;
A[i+1] = B[i+1] * 4;
A[i+2] = B[i+2] * 4;
A[i+3] = B[i+3] * 4;
}
}
The code was casting the SCEV-expanded code for the new
induction variable to a phi-node. When the loop had a non-constant
lower bound, the SCEV expander would end the code expansion with an
add insted of a phi node and the cast would fail.
It looks like the cast to a phi node was only needed to get the
induction variable value coming from the backedge to compute the end
of loop condition. This patch changes the loop reroller to compare
the induction variable to the number of times the backedge is taken
instead of the iteration count of the loop. In other words, we stop
the loop when the current value of the induction variable ==
IterationCount-1. Previously, the comparison was comparing the
induction variable value from the next iteration == IterationCount.
This problem only seems to occur on 32-bit targets. For some reason,
the loop is not rerolled on 64-bit targets.
PR18290
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198425 91177308-0d34-0410-b5e6-96231b3b80d8
cycles
This allows the value equality check to work even if we don't have a dominator
tree. Also add some more comments.
I was worried about compile time impacts and did not implement reachability but
used the dominance check in the initial patch. The trade-off was that the
dominator tree was required.
The llvm utility function isPotentiallyReachable cuts off the recursive search
after 32 visits. Testing did not show any compile time regressions showing my
worries unjustfied.
No compile time or performance regressions at O3 -flto -mavx on test-suite +
externals.
Addresses review comments from r198290.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198400 91177308-0d34-0410-b5e6-96231b3b80d8
Reverting due to bot failure I won't have time to investigate until
tomorrow.
This reverts commit r198397.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198398 91177308-0d34-0410-b5e6-96231b3b80d8
What's good for LTO metadata size problems ought to be good for non-LTO
debug info size too, so let's rely on the same uniqueness in both cases.
If it's insufficient for non-LTO for whatever reason (since we now won't
be uniquing CU-local types or any C types - but these are likely to not
be the most significant contributors to type bloat) we should consider a
frontend solution that'll help both LTO and non-LTO alike, rather than
using DWARF-level DIE-hashing that only helps non-LTO debug info size.
It's also much simpler this way and benefits C++ even more since we can
deduplicate lexically separate definitions of the same C++ type since
they have the same mangled name.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198397 91177308-0d34-0410-b5e6-96231b3b80d8
The cgo problem was that it wants dwarf2 which doesn't support direct
constant encoding of the location. So let's add support for dwarf2
encoding (using a location expression) of data member locations.
This reverts commit r198385.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198389 91177308-0d34-0410-b5e6-96231b3b80d8
Apologies for the noise - we're seeing some Go failures with cgo
interacting with Clang's debug info due to this change.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198385 91177308-0d34-0410-b5e6-96231b3b80d8
The greedy register allocator tries to split a live-range around each
instruction where it is used or defined to relax the constraints on the entire
live-range (this is a last chance split before falling back to spill).
The goal is to have a big live-range that is unconstrained (i.e., that can use
the largest legal register class) and several small local live-range that carry
the constraints implied by each instruction.
E.g.,
Let csti be the constraints on operation i.
V1=
op1 V1(cst1)
op2 V1(cst2)
V1 live-range is constrained on the intersection of cst1 and cst2.
tryInstructionSplit relaxes those constraints by aggressively splitting each
def/use point:
V1=
V2 = V1
V3 = V2
op1 V3(cst1)
V4 = V2
op2 V4(cst2)
Because of how the coalescer infrastructure works, each new variable (V3, V4)
that is alive at the same time as V1 (or its copy, here V2) interfere with V1.
Thus, we end up with an uncoalescable copy for each split point.
To make tryInstructionSplit less aggressive, we check if the split point
actually relaxes the constraints on the whole live-range. If it does not, we do
not insert it.
Indeed, it will not help the global allocation problem:
- V1 will have the same constraints.
- V1 will have the same interference + possibly the newly added split variable
VS.
- VS will produce an uncoalesceable copy if alive at the same time as V1.
<rdar://problem/15570057>
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198369 91177308-0d34-0410-b5e6-96231b3b80d8