Prior to this, fixed point multiplication would lead to this assertion
error on AArhc64, armv8, and armv7.
```
_Accum f(_Accum x, _Accum y) { return x * y; }
// ./bin/clang++ -ffixed-point /tmp/test2.cc -c -S -o - -target aarch64 -O3
clang++: llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp:10245: void llvm::TargetLowering::forceExpandWideMUL(SelectionDAG &, const SDLoc &, bool, EVT, const SDValue, const SDValue, const SDValue, const SDValue, SDValue &, SDValue &) const: Assertion `Ret.getOpcode() == ISD::MERGE_VALUES && "Ret value is a collection of constituent nodes holding result."' failed.
```
This path into forceExpandWideMUL should only be taken if we don't
support [US]MUL_LOHI or MULH[US] for the operand size (32 in this case).
But we should also check if we can just leverage regular wide
multiplication. That is, extend the operands from 32 to 64, do a regular
64-bit mul, then trunc and shift. These ops are certainly available on
aarch64 but for wider types.
According to langref, llvm.maximum/minimum has -0.0 < +0.0 semantics and
propagates NaN.
Expand the nodes on targets not supporting the operation, by adding
extra check for NaN and using is_fpclass to check zero signs.
The load narrowing part of TargetLowering::SimplifySetCC is updated
according to this:
1) The offset calculation (for big endian) did not work properly for
non byte-sized types. This is basically solved by an early exit
if the memory type isn't byte-sized. But the code is also corrected
to use the store size when calculating the offset.
2) To still allow some optimizations for non-byte-sized types the
TargetLowering::isPaddedAtMostSignificantBitsWhenStored hook is
added. By default it assumes that scalar integer types are padded
starting at the most significant bits, if the type needs padding
when being stored to memory.
3) Allow optimizing when isPaddedAtMostSignificantBitsWhenStored is
true, as that hook makes it possible for TargetLowering to know
how the non byte-sized value is aligned in memory.
4) Update the algorithm to always search for a narrowed load with
a power-of-2 byte-sized type. In the past the algorithm started
with the the width of the original load, and then divided it by
two for each iteration. But for a type such as i48 that would
just end up trying to narrow the load into a i24 or i12 load,
and then we would fail sooner or later due to not finding a
newVT that fulfilled newVT.isRound().
With this new approach we can narrow the i48 load into either
an i8, i16 or i32 load. By checking if such a load is allowed
(e.g. alignment wise) for any "multiple of 8 offset", then we can find
more opportunities for the optimization to trigger. So even for a
byte-sized type such as i32 we may now end up narrowing the load
into loading the 16 bits starting at offset 8 (if that is allowed
by the target). The old algorithm did not even consider that case.
5) Also start using getObjectPtrOffset instead of getMemBasePlusOffset
when creating the new ptr. This way we get "nsw" on the add.
The current APInt::multiplicativeInverse takes a modulus which can be
any value, but all in-tree callers use a power of two. Moreover, most
callers want to use two to the power of the width of an existing APInt,
which is awkward because 2^N is not representable as an N-bit APInt.
Add a new overload of multiplicativeInverse which implicitly uses
2^BitWidth as the modulus.
Reverse the fold with handling inside canCreateUndefOrPoison for cases where we know that the extract index is in bounds.
This exposed a number or regressions, and required some initial freeze handling of SCALAR_TO_VECTOR, which will require us to properly improve demandedelts support to handle its undef upper elements.
There is still one outstanding regression to be addressed in the future - how do we want to handle folds involving frozen loads?
Fixes#86968
Allow targets to rely on TargetLowering::isGuaranteedNotToBeUndefOrPoisonForTargetNode to test nodes for canCreateUndefOrPoisonForTargetNode + all arguments are isGuaranteedNotToBeUndefOrPoison.
Targets can still perform this themselves for specific special case nodes (e.g. target shuffles).
Matches the fallback in SelectionDAG::isGuaranteedNotToBeUndefOrPoison
This reverts commit 353fbeb0a294d2c7cef6d88607fa0fd50ee81462. It crashes
when it encounters an UINT_TO_FP.
llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp:1618 in SDValue llvm::SelectionDAG::getConstant(const ConstantInt &, const SDLoc &, EVT, bool, bool): VT.isInteger() && "Cannot create FP integer constant!"
The expansion previously used, derived from Hacker's Delight,
does not work correctly when the dividend is INT_MIN and the
divisor is a power of two. We now use an alternate derivation
of the A and Q constants specifically for the power-of-two divisor
case to avoid this problem. Credit to Fabian Giesen for the
new derivation.
Fixes https://github.com/llvm/llvm-project/issues/77169
The logic was supposed to be choosing between {0, 1, -1} as an
adjustment to the FP bit pattern. However, the adjustment itself was
used as the bit pattern instead which result in garbage results.
We did something pretty naive:
- round FP64 -> BF16 by first rounding to FP32
- skip FP32 -> BF16 rounding entirely
- taking the top 16 bits of a FP32 which will turn some NaNs into
infinities
Let's do this in a more principled way by rounding types with more
precision than FP32 to FP32 using round-inexact-to-odd which will negate
double rounding issues.
sext_inreg is our canonical form of shift pair before op legalization so
DAG combiner will probably create it anyway. If it isn't legal
LegalizeDAG will expand to shifts later.
If we have a `SETCC (SETCC), 0, NE` and ZeroOrOneBooleanContent, we can remove
the outer setcc as it will produce the same value as the inner. This can be
generalized to anything where the top bits are known to be 0, as the value will
remain as 1 or 0.
32-bit ARMv6 with thumb doesn't support MULHS/MUL_LOHI as legal/custom
nodes during expansion which will cause fixed point multiplication of
_Accum types to fail with fixed point arithmetic. Prior to this, we just
happen to use fixed point multiplication on platforms that happen to
support these MULHS/MUL_LOHI.
This patch attempts to check if the multiplication can be done via
libcalls, which are provided by the arm runtime. These libcall attempts
are made elsewhere, so this patch refactors that libcall logic into its
own functions and the fixed point expansion calls and reuses that logic.
We do the same for the analogous transform in DAGCombine, but this case
was missed in the recent patch which added support for zext nneg.
Sorry for the lack of test coverage. Not sure how to exercise this piece
of logic. It appears to have only minimal impact on LIT tests (only
test/CodeGen/X86/wide-scalar-shift-by-byte-multiple-legalization.ll),
and even then, the changes without it appear uninteresting. Maybe we
should remove this transform instead?
This is the logical equivalent for #76710 for APInt and uses the same
naming scheme.
Converted existing users through:
`git grep -l "cast<ConstantSDNode>\(.*\).*getAPIntValueValue" | xargs
sed -E -i
's/cast<ConstantSDNode>\((.*)\)->getAPIntValue/\1->getAsAPIntVal/'`
For targets that use 0/-1 boolean results, we want to keep this pattern through extensions/truncations as much as possible - so avoid simplifying to any_extend even if we don't demand the upper bits.
Noticed in triage for https://reviews.llvm.org/D152928
This atempts to fix#76734 which is a crash in invalid TRUNC nodes types
from unoptimized input code in combineShiftToAVG. The NVT can be VT if
the larger type was legal and the adds will not overflow, in which case
the inputs should be extended.
From what I can tell this appears to be valid (if not optimal for this
case): https://alive2.llvm.org/ce/z/fRieHR
The result has also been changed to getExtOrTrunc in case that VT==NVT,
which is not handled by SEXT/ZEXT.
This copies the flag from IR to the SDNode in SelectionDAGBuilder, clears
the flag in SimplifyDemandedBits, and adds it to canCreateUndefOrPoison.
Uses of the flag will come in later patches.
It seems TypeSize is currently broken in the sense that:
TypeSize::Fixed(4) + TypeSize::Scalable(4) => TypeSize::Fixed(8)
without failing its assert that explicitly tests for this case:
assert(LHS.Scalable == RHS.Scalable && ...);
The reason this fails is that `Scalable` is a static method of class
TypeSize,
and LHS and RHS are both objects of class TypeSize. So this is
evaluating
if the pointer to the function Scalable == the pointer to the function
Scalable,
which is always true because LHS and RHS have the same class.
This patch fixes the issue by renaming `TypeSize::Scalable` ->
`TypeSize::getScalable`, as well as `TypeSize::Fixed` to
`TypeSize::getFixed`,
so that it no longer clashes with the variable in
FixedOrScalableQuantity.
The new methods now also better match the coding standard, which
specifies that:
* Variable names should be nouns (as they represent state)
* Function names should be verb phrases (as they represent actions)
When x is not known to be nonzero, ctpop(x) == 1 is expanded to
x != 0 && (x & (x - 1)) == 0
resulting in codegen like
leal -1(%rdi), %eax
testl %eax, %edi
sete %cl
testl %edi, %edi
setne %al
andb %cl, %al
But another expression that works is
(x ^ (x - 1)) > x - 1
which has nicer codegen:
leal -1(%rdi), %eax
xorl %eax, %edi
cmpl %eax, %edi
seta %al
This patch lowers `sdiv x, +/-2**k` to `add + select + shift` when the
short forward branch optimization is enabled. The latter inst seq
performs faster than the seq generated by target-independent
DAGCombiner. This algorithm is described in ***Hacker's Delight***.
This patch also removes duplicate logic in the X86 and AArch64 backend.
But we cannot do this for the PowerPC backend since it generates a
special instruction `addze`.
This adds the nneg flag to SDNodeFlags and the node printing code.
SelectionDAGBuilder will add this flag to the node if the target doesn't
prefer sign extend.
A future RISC-V patch can remove the sign extend preference from
SelectionDAGBuilder.
I've also added the flag to the DAG combine that converts
ISD::SIGN_EXTEND to ISD::ZERO_EXTEND.
D146121 needs to set the NSW flag, but given the result is NUW then we know that the result has leading zeros, so we don't need to call ComputeNumSignBits - just reuse the existing KnownBits value instead.
If a shl node leaves the upper half bits zero / undemanded, then see if we can profitably perform this with a half-width shl and a free trunc/zext.
Followup to D146121
Reapplied - moved after the ShrinkDemandedOp call; reuse the existing KnownBits result; ensure that we only attempt this if all the upper bits are demanded; 547dc461225ba should address the remaining regressions that were noticed in the previous commit.
Differential Revision: https://reviews.llvm.org/D155472
If a shl node leaves the upper half bits zero / undemanded, then see if we can profitably perform this with a half-width shl and a free trunc/zext.
Followup to D146121
Differential Revision: https://reviews.llvm.org/D155472
Splitting up patches for #20571. I found these comments generally useful
to add and not predicated on those changes. Hopefully they help future
travelers.
I accidentally introduced this in
commit 330fa7d2a4e0 ("[TargetLowering] Deduplicate choosing InlineAsm
constraint between ISels (#67057)")
Fix forward.
After 330fa7d2a4e0cfbb4b078 we were seeing nondeterministic failures of
llvm/test/CodeGen/ARM/thumb-big-stack.ll, with different code being
generated in different runs.
Switching sort -> stable_sort fixes this.
It looks like the old algorithm picked the first best option, and using
stable_sort restores that behavior.
