Ignore incoming values with constant false masks when trying to simplify
VPBlendRecipes.
As a follow-on optimization, we should also be able to drop all incoming
values with false masks by creating a new VPBlendRecipe with those
operands dropped.
PR: https://github.com/llvm/llvm-project/pull/89384
In #88217 a large set of matchers was changed to only accept poison
values in splats, but not undef values. This is because we now use
poison for non-demanded vector elements, and allowing undef can cause
correctness issues.
This patch covers the remaining matchers by changing the AllowUndef
parameter of getSplatValue() to AllowPoison instead. We also carry out
corresponding renames in matchers.
As a followup, we may want to change the default for things like m_APInt
to m_APIntAllowPoison (as this is much less risky when only allowing
poison), but this change doesn't do that.
There is one caveat here: We have a single place
(X86FixupVectorConstants) which does require handling of vector splats
with undefs. This is because this works on backend constant pool
entries, which currently still use undef instead of poison for
non-demanded elements (because SDAG as a whole does not have an explicit
poison representation). As it's just the single use, I've open-coded a
getSplatValueAllowUndef() helper there, to discourage use in any other
places.
Recommit with a fix for the use-after-free causing the revert.
This reverts the revert commit f872043e055f4163c3c4b1b86ca0354490174987.
Original commit message:
Dropping disjoint from an OR may yield incorrect results, as some
analysis may have converted it to an Add implicitly (e.g. SCEV used for
dependence analysis). Instead, replace it with an equivalent Add.
This is possible as all users of the disjoint OR only access lanes where
the operands are disjoint or poison otherwise.
Note that replacing all disjoint ORs with ADDs instead of dropping the
flags is not strictly necessary. It is only needed for disjoint ORs that
SCEV treated as ADDs, but those are not tracked.
There are other places that may drop poison-generating flags; those
likely need similar treatment.
Fixes https://github.com/llvm/llvm-project/issues/81872
PR: https://github.com/llvm/llvm-project/pull/83821
This reverts commit c2c1e6ee4ce0df3d000ba880fa6cf58441da6462. It creates
a use after free.
==8342==ERROR: AddressSanitizer: heap-use-after-free on address 0x50f000001760 at pc 0x55b9fb84a8fb bp 0x7ffc18468a10 sp 0x7ffc18468a08
READ of size 1 at 0x50f000001760 thread T0
#0 0x55b9fb84a8fa in dropPoisonGeneratingFlags llvm/lib/Transforms/Vectorize/VPlan.h:1040:13
#1 0x55b9fb84a8fa in llvm::VPlanTransforms::dropPoisonGeneratingRecipes(llvm::VPlan&, llvm::function_ref<bool (llvm::BasicBlock*)>)::$_0::operator()(llvm::VPRecipeBase*) const llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp:1236:23
#2 0x55b9fb84a196 in llvm::VPlanTransforms::dropPoisonGeneratingRecipes(llvm::VPlan&, llvm::function_ref<bool (llvm::BasicBlock*)>) llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
Can be reproduced with asan on
Transforms/LoopVectorize/AArch64/sve-interleaved-masked-accesses.ll
Transforms/LoopVectorize/X86/pr81872.ll
Transforms/LoopVectorize/X86/x86-interleaved-accesses-masked-group.ll
Dropping disjoint from an OR may yield incorrect results, as some
analysis may have converted it to an Add implicitly (e.g. SCEV used for
dependence analysis). Instead, replace it with an equivalent Add.
This is possible as all users of the disjoint OR only access lanes where
the operands are disjoint or poison otherwise.
Note that replacing all disjoint ORs with ADDs instead of dropping the
flags is not strictly necessary. It is only needed for disjoint ORs that
SCEV treated as ADDs, but those are not tracked.
There are other places that may drop poison-generating flags; those
likely need similar treatment.
Fixes https://github.com/llvm/llvm-project/issues/81872
PR: https://github.com/llvm/llvm-project/pull/83821
Generalize pattern matchers to take recipe types to match as template
arguments and use it to provide matchers for unary and binary recipes
with specific opcodes and a list of recipe types (VPWidenRecipe,
VPReplicateRecipe, VPWidenCastRecipe, VPInstruction)
The new matchers are used to simplify and generalize the code in
simplifyRecipes.
