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[GVN] Teach GVN simple masked load/store forwarding #157689

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Merged
MDevereau merged 6 commits into from
Oct 3, 2025
Merged

[GVN] Teach GVN simple masked load/store forwarding #157689

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11ac166
[GVN] Teach GVN simple masked load/store forwarding
MDevereau Sep 5, 2025
c335ed6
Use PatternMatch
MDevereau Sep 10, 2025
0d7107f
Remove intrinsic declarations
MDevereau Sep 10, 2025
8f7fe4a
Respond to david-arm's review comments
MDevereau Sep 23, 2025
a3a6f9f
Remove pointer check and extra test
MDevereau Sep 29, 2025
6693704
Add bail and test for type mismatch
MDevereau Sep 30, 2025
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2 changes: 2 additions & 0 deletions llvm/include/llvm/Transforms/Scalar/GVN.h
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Expand Up @@ -56,6 +56,7 @@ class OptimizationRemarkEmitter;
class PHINode;
class TargetLibraryInfo;
class Value;
class IntrinsicInst;
/// A private "module" namespace for types and utilities used by GVN. These
/// are implementation details and should not be used by clients.
namespace LLVM_LIBRARY_VISIBILITY_NAMESPACE gvn {
Expand Down Expand Up @@ -349,6 +350,7 @@ class GVNPass : public PassInfoMixin<GVNPass> {

// Helper functions of redundant load elimination.
bool processLoad(LoadInst *L);
bool processMaskedLoad(IntrinsicInst *I);
bool processNonLocalLoad(LoadInst *L);
bool processAssumeIntrinsic(AssumeInst *II);

Expand Down
46 changes: 46 additions & 0 deletions llvm/lib/Transforms/Scalar/GVN.cpp
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Expand Up @@ -50,6 +50,7 @@
#include "llvm/IR/DebugLoc.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
Expand Down Expand Up @@ -2287,6 +2288,46 @@ bool GVNPass::processLoad(LoadInst *L) {
return true;
}

// Attempt to process masked loads which have loaded from
// masked stores with the same mask
bool GVNPass::processMaskedLoad(IntrinsicInst *I) {
Value *Mask = I->getOperand(2);
Value *Passthrough = I->getOperand(3);

MemDepResult Dep = MD->getDependency(I);
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@david-arm david-arm Sep 18, 2025

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Looking at processLoad it seems like you need an additional check:

  if (!MD)
    return false;

Would be good to add a test for this too.

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@MDevereau MDevereau Sep 23, 2025

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I've added the test masked-load-store-no-mem-dep.ll to deal with this.

Instruction *DepInst = Dep.getInst();
if (!DepInst || !Dep.isLocal())
return false;

Value *StoreVal;
if (!match(DepInst,
m_Intrinsic<Intrinsic::masked_store>(m_Value(StoreVal), m_Value(),
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@david-arm david-arm Sep 18, 2025 •
edited
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Might be worth adding an equivalent m_MaskedStore to llvm/IR/PatternMatch.h and using that instead?

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@MDevereau MDevereau Sep 23, 2025

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Done. Though, I wonder how many intrinsics warrant a specific match before it becomes a bit of a code bloat.

m_Value(), m_Specific(Mask))))
return false;

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@david-arm david-arm Sep 18, 2025

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If a dependency is local then it's either a Clobber or a Def, and it looks like the code below is assuming a Def. Would be good to clarify this. If so, I think you have to bail out for the clobber case as that's more complicated - see AnalyzeLoadAvailability.

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@MDevereau MDevereau Sep 23, 2025

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I added a bail-out if it's not a Def

Value *OpToForward = nullptr;
if (match(StoreVal, m_MaskedLoad(m_Value(), m_Value(), m_Specific(Mask),
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@david-arm david-arm Sep 18, 2025

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It feels a bit wrong to be testing the stored value here - it's an extra level of complexity that I don't think you need. I'd expect that if you always create a select like you do below, that instcombine would fold the select into the masked load anyway if the passthru matches. If instcombine doesn't do that, then perhaps worth adding that pattern?

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@MDevereau MDevereau Sep 23, 2025

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As it stands I don't believe said InstCombine exists: https://godbolt.org/z/K835KeW1d. I think what you're proposing is a more elegant way to reach the end result though.

m_Specific(Passthrough))))
// For MaskedLoad->MaskedStore->MaskedLoad, the mask must be the same for
// all three instructions. The Passthrough on the two loads must also be the
// same.
OpToForward = AvailableValue::get(StoreVal).getSimpleValue();
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@david-arm david-arm Sep 18, 2025

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I don't think there is any value in calling AvailableValue::get(StoreVal).getSimpleValue() because that's identical to just doing:

  OpToForward = StoreVal;

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@MDevereau MDevereau Sep 23, 2025

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I've removed the AvailableValue call.

else if (match(StoreVal, m_Intrinsic<Intrinsic::masked_load>()))
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@david-arm david-arm Sep 18, 2025

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I think if you're hitting masked loads here it might be because you're permitting "clobbers". What happens if you bail out for clobbers as I mentioned above?

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@MDevereau MDevereau Sep 23, 2025

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The test @bail_on_different_passthrough I added to masked-load-store.ll removes a load when excluding clobbers. I think it's OK since it falls to the else case where the inactive select lanes are the passthrough value, so i've renamed the test to generate_sel_with_passthrough

That being said, removing the matches for StoreVal which you suggested here and always generating a select removes the need for this else if clause anyway.

return false;
else {
// MaskedStore(Op, ptr, mask)->MaskedLoad(ptr, mask, passthrough) can be
// replaced with MaskedStore(Op, ptr, mask)->select(mask, Op, passthrough)
IRBuilder<> Builder(I);
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@david-arm david-arm Sep 18, 2025

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It looks like GVN.cpp typically doesn't use IRBuilder and prefers to create instructions and insert them manually, i.e.

  PHINode *Phi = PHINode::Create(CurInst->getType(), PredMap.size(),
                                 CurInst->getName() + ".pre-phi");
  Phi->insertBefore(CurrentBlock->begin());

Having said that, I don't see ac actual problem with using IRBuilder.

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@MDevereau MDevereau Sep 23, 2025

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I've replaced it with Select::CreateInst, it avoids an extra #include which is nice

OpToForward = Builder.CreateSelect(Mask, StoreVal, Passthrough);
}

I->replaceAllUsesWith(OpToForward);
ICF->removeUsersOf(I);
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@david-arm david-arm Sep 18, 2025

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I don't if ordering matters, but I noticed that in processLoads we do this the other way around:

  ICF->removeUsersOf(L);
  L->replaceAllUsesWith(AvailableValue);

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@MDevereau MDevereau Sep 23, 2025

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Done.

salvageAndRemoveInstruction(I);
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@david-arm david-arm Sep 18, 2025

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Do we also need to call

  if (MSSAU)
    MSSAU->removeMemoryAccess(L);

and

  if (MD && AvailableValue->getType()->isPtrOrPtrVectorTy())
    MD->invalidateCachedPointerInfo(AvailableValue);

similar to processLoads?

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@MDevereau MDevereau Sep 23, 2025

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if (MSSAU)
  MSSAU->removeMemoryAccess(L);

This is indirectly called by

salvageAndRemoveInstruction(I)
//...
removeInstruction(I)

I've added the Pointer stuff though.

++NumGVNLoad;
return true;
}

/// Return a pair the first field showing the value number of \p Exp and the
/// second field showing whether it is a value number newly created.
std::pair<uint32_t, bool>
Expand Down Expand Up @@ -2734,6 +2775,11 @@ bool GVNPass::processInstruction(Instruction *I) {
return false;
}

if (auto *II = dyn_cast<IntrinsicInst>(I))
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@david-arm david-arm Sep 18, 2025

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I think you can simplify this a little by doing something like:

  if (match(I, m_Intrinsic<Intrinsic::masked_load>()) && processMaskedLoad(cast<IntrinsicInst>(I)))
    return true;

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@MDevereau MDevereau Sep 23, 2025

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Done.

if (II && II->getIntrinsicID() == Intrinsic::masked_load)
if (processMaskedLoad(II))
return true;

// For conditional branches, we can perform simple conditional propagation on
// the condition value itself.
if (BranchInst *BI = dyn_cast<BranchInst>(I)) {
Expand Down
149 changes: 147 additions & 2 deletions llvm/test/Transforms/GVN/masked-load-store.ll
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Expand Up @@ -36,6 +36,151 @@ define <128 x i8> @f1(ptr %a0, <128 x i8> %a1, <128 x i8> %a2) {
ret <128 x i8> %v4
}

declare <128 x i8> @llvm.masked.load.v128i8.p0(ptr, i32, <128 x i1>, <128 x i8>)
declare void @llvm.masked.store.v128i8.p0(<128 x i8>, ptr, i32, <128 x i1>)
define <4 x float> @forward_masked_load(ptr %0, ptr %1) {
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@david-arm david-arm Sep 29, 2025

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Might be worth having a test for an arbitrary mask as well that's passed in as a function argument, i.e. we can apply the optimisation even if the mask isn't known to come from get.active.lane.mask.

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@MDevereau MDevereau Sep 29, 2025

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I've added forward_masked_load_arbitrary_mask

; CHECK-LABEL: @forward_masked_load(
; CHECK-NEXT: [[TMP4:%.*]] = call <4 x float> @llvm.masked.load.v4f32.p0(ptr [[TMP0:%.*]], i32 1, <4 x i1> splat (i1 true), <4 x float> zeroinitializer)
; CHECK-NEXT: call void @llvm.masked.store.v4f32.p0(<4 x float> [[TMP4]], ptr [[TMP1:%.*]], i32 1, <4 x i1> splat (i1 true))
; CHECK-NEXT: ret <4 x float> [[TMP4]]
;
%mask = call <4 x i1> @llvm.get.active.lane.mask.v4i1.i32(i32 0, i32 4)
%load1 = call <4 x float> @llvm.masked.load.v4f32.p0(ptr %0, i32 1, <4 x i1> %mask, <4 x float> zeroinitializer)
call void @llvm.masked.store.v4f32.p0(<4 x float> %load1, ptr %1, i32 1, <4 x i1> %mask)
%load2 = call <4 x float> @llvm.masked.load.v4f32.p0(ptr %1, i32 1, <4 x i1> %mask, <4 x float> zeroinitializer)
ret <4 x float> %load2
}

define <4 x float> @forward_binop_splat_i1_mask(ptr %0, ptr %1) {
; CHECK-LABEL: @forward_binop_splat_i1_mask(
; CHECK-NEXT: [[LOAD_0_0:%.*]] = call <4 x float> @llvm.masked.load.v4f32.p0(ptr [[TMP0:%.*]], i32 1, <4 x i1> splat (i1 true), <4 x float> zeroinitializer)
; CHECK-NEXT: [[GEP_0_16:%.*]] = getelementptr i8, ptr [[TMP0]], i32 16
; CHECK-NEXT: [[LOAD_0_16:%.*]] = call <4 x float> @llvm.masked.load.v4f32.p0(ptr [[GEP_0_16]], i32 1, <4 x i1> splat (i1 true), <4 x float> zeroinitializer)
; CHECK-NEXT: [[FMUL:%.*]] = fmul <4 x float> [[LOAD_0_0]], [[LOAD_0_16]]
; CHECK-NEXT: call void @llvm.masked.store.v4f32.p0(<4 x float> [[FMUL]], ptr [[TMP1:%.*]], i32 1, <4 x i1> splat (i1 true))
; CHECK-NEXT: ret <4 x float> [[FMUL]]
;
%mask = tail call <4 x i1> @llvm.get.active.lane.mask.v4i1.i32(i32 0, i32 4)
%load.0.0 = call <4 x float> @llvm.masked.load.v4f32.p0(ptr %0, i32 1, <4 x i1> %mask, <4 x float> zeroinitializer)
%gep.0.16 = getelementptr i8, ptr %0, i32 16
%load.0.16 = call <4 x float> @llvm.masked.load.v4f32.p0(ptr %gep.0.16, i32 1, <4 x i1> %mask, <4 x float> zeroinitializer)
%fmul = fmul <4 x float> %load.0.0, %load.0.16
call void @llvm.masked.store.v4f32.p0(<4 x float> %fmul, ptr %1, i32 1, <4 x i1> %mask)
%load.1.0 = call <4 x float> @llvm.masked.load.v4f32.p0(ptr %1, i32 1, <4 x i1> %mask, <4 x float> zeroinitializer)
ret <4 x float> %load.1.0
}

define <4 x float> @forward_binop_with_sel(ptr %0, ptr %1, i32 %a, i32 %b, <4 x float> %passthrough) {
; CHECK-LABEL: @forward_binop_with_sel(
; CHECK-NEXT: [[MASK:%.*]] = tail call <4 x i1> @llvm.get.active.lane.mask.v4i1.i32(i32 [[A:%.*]], i32 [[B:%.*]])
; CHECK-NEXT: [[LOAD_0_0:%.*]] = call <4 x float> @llvm.masked.load.v4f32.p0(ptr [[TMP0:%.*]], i32 1, <4 x i1> [[MASK]], <4 x float> zeroinitializer)
; CHECK-NEXT: [[GEP_0_16:%.*]] = getelementptr i8, ptr [[TMP0]], i32 16
; CHECK-NEXT: [[LOAD_0_16:%.*]] = call <4 x float> @llvm.masked.load.v4f32.p0(ptr [[GEP_0_16]], i32 1, <4 x i1> [[MASK]], <4 x float> zeroinitializer)
; CHECK-NEXT: [[FMUL:%.*]] = fmul <4 x float> [[LOAD_0_0]], [[LOAD_0_16]]
; CHECK-NEXT: call void @llvm.masked.store.v4f32.p0(<4 x float> [[FMUL]], ptr [[TMP1:%.*]], i32 1, <4 x i1> [[MASK]])
; CHECK-NEXT: [[TMP3:%.*]] = select <4 x i1> [[MASK]], <4 x float> [[FMUL]], <4 x float> [[PASSTHROUGH:%.*]]
; CHECK-NEXT: ret <4 x float> [[TMP3]]
;
%mask = tail call <4 x i1> @llvm.get.active.lane.mask.v4i1.i32(i32 %a, i32 %b)
%load.0.0 = call <4 x float> @llvm.masked.load.v4f32.p0(ptr %0, i32 1, <4 x i1> %mask, <4 x float> zeroinitializer)
%gep.0.16 = getelementptr i8, ptr %0, i32 16
%load.0.16 = call <4 x float> @llvm.masked.load.v4f32.p0(ptr %gep.0.16, i32 1, <4 x i1> %mask, <4 x float> zeroinitializer)
%fmul = fmul <4 x float> %load.0.0, %load.0.16
call void @llvm.masked.store.v4f32.p0(<4 x float> %fmul, ptr %1, i32 1, <4 x i1> %mask)
%load.1.0 = call <4 x float> @llvm.masked.load.v4f32.p0(ptr %1, i32 1, <4 x i1> %mask, <4 x float> %passthrough)
ret <4 x float> %load.1.0
}

define <vscale x 4 x float> @forward_masked_load_scalable(ptr %0, ptr %1, <vscale x 4 x float> %passthrough) {
; CHECK-LABEL: @forward_masked_load_scalable(
; CHECK-NEXT: [[TMP3:%.*]] = call <vscale x 4 x i1> @llvm.get.active.lane.mask.nxv4i1.i32(i32 0, i32 4)
; CHECK-NEXT: [[TMP4:%.*]] = call <vscale x 4 x float> @llvm.masked.load.nxv4f32.p0(ptr [[TMP0:%.*]], i32 1, <vscale x 4 x i1> [[TMP3]], <vscale x 4 x float> [[PASSTHROUGH:%.*]])
; CHECK-NEXT: call void @llvm.masked.store.nxv4f32.p0(<vscale x 4 x float> [[TMP4]], ptr [[TMP1:%.*]], i32 1, <vscale x 4 x i1> [[TMP3]])
; CHECK-NEXT: ret <vscale x 4 x float> [[TMP4]]
;
%mask = call <vscale x 4 x i1> @llvm.get.active.lane.mask.nxv4i1.i32(i32 0, i32 4)
%load1 = call <vscale x 4 x float> @llvm.masked.load.nxv4f32.p0(ptr %0, i32 1, <vscale x 4 x i1> %mask, <vscale x 4 x float> %passthrough)
call void @llvm.masked.store.nxv4f32.p0(<vscale x 4 x float> %load1, ptr %1, i32 1, <vscale x 4 x i1> %mask)
%load2 = call <vscale x 4 x float> @llvm.masked.load.nxv4f32.p0(ptr %1, i32 1, <vscale x 4 x i1> %mask, <vscale x 4 x float> %passthrough)
ret <vscale x 4 x float> %load2
}

define <vscale x 4 x float> @bail_on_different_passthrough(ptr %0, ptr %1, <vscale x 4 x float> %passthrough) {
; CHECK-LABEL: @bail_on_different_passthrough(
; CHECK-NEXT: [[TMP3:%.*]] = call <vscale x 4 x i1> @llvm.get.active.lane.mask.nxv4i1.i32(i32 0, i32 4)
; CHECK-NEXT: [[TMP4:%.*]] = call <vscale x 4 x float> @llvm.masked.load.nxv4f32.p0(ptr [[TMP0:%.*]], i32 1, <vscale x 4 x i1> [[TMP3]], <vscale x 4 x float> zeroinitializer)
; CHECK-NEXT: call void @llvm.masked.store.nxv4f32.p0(<vscale x 4 x float> [[TMP4]], ptr [[TMP1:%.*]], i32 1, <vscale x 4 x i1> [[TMP3]])
; CHECK-NEXT: [[TMP5:%.*]] = call <vscale x 4 x float> @llvm.masked.load.nxv4f32.p0(ptr [[TMP1]], i32 1, <vscale x 4 x i1> [[TMP3]], <vscale x 4 x float> [[PASSTHROUGH:%.*]])
; CHECK-NEXT: ret <vscale x 4 x float> [[TMP5]]
;
%mask = call <vscale x 4 x i1> @llvm.get.active.lane.mask.nxv4i1.i32(i32 0, i32 4)
%load1 = call <vscale x 4 x float> @llvm.masked.load.nxv4f32.p0(ptr %0, i32 1, <vscale x 4 x i1> %mask, <vscale x 4 x float> zeroinitializer)
call void @llvm.masked.store.nxv4f32.p0(<vscale x 4 x float> %load1, ptr %1, i32 1, <vscale x 4 x i1> %mask)
%load2 = call <vscale x 4 x float> @llvm.masked.load.nxv4f32.p0(ptr %1, i32 1, <vscale x 4 x i1> %mask, <vscale x 4 x float> %passthrough)
ret <vscale x 4 x float> %load2
}

define <vscale x 4 x float> @forward_binop_with_sel_scalable(ptr %0, ptr %1, <vscale x 4 x float> %passthrough) {
; CHECK-LABEL: @forward_binop_with_sel_scalable(
; CHECK-NEXT: [[MASK:%.*]] = tail call <vscale x 4 x i1> @llvm.get.active.lane.mask.nxv4i1.i32(i32 0, i32 4)
; CHECK-NEXT: [[LOAD_0_0:%.*]] = call <vscale x 4 x float> @llvm.masked.load.nxv4f32.p0(ptr [[TMP0:%.*]], i32 1, <vscale x 4 x i1> [[MASK]], <vscale x 4 x float> zeroinitializer)
; CHECK-NEXT: [[GEP_0_16:%.*]] = getelementptr i8, ptr [[TMP0]], i32 16
; CHECK-NEXT: [[LOAD_0_16:%.*]] = call <vscale x 4 x float> @llvm.masked.load.nxv4f32.p0(ptr [[GEP_0_16]], i32 1, <vscale x 4 x i1> [[MASK]], <vscale x 4 x float> zeroinitializer)
; CHECK-NEXT: [[FMUL:%.*]] = fmul <vscale x 4 x float> [[LOAD_0_0]], [[LOAD_0_16]]
; CHECK-NEXT: call void @llvm.masked.store.nxv4f32.p0(<vscale x 4 x float> [[FMUL]], ptr [[TMP1:%.*]], i32 1, <vscale x 4 x i1> [[MASK]])
; CHECK-NEXT: [[TMP3:%.*]] = select <vscale x 4 x i1> [[MASK]], <vscale x 4 x float> [[FMUL]], <vscale x 4 x float> [[PASSTHROUGH:%.*]]
; CHECK-NEXT: ret <vscale x 4 x float> [[TMP3]]
;
%mask = tail call <vscale x 4 x i1> @llvm.get.active.lane.mask.nxv4i1.i32(i32 0, i32 4)
%load.0.0 = call <vscale x 4 x float> @llvm.masked.load.nxv4f32.p0(ptr %0, i32 1, <vscale x 4 x i1> %mask, <vscale x 4 x float> zeroinitializer)
%gep.0.16 = getelementptr i8, ptr %0, i32 16
%load.0.16 = call <vscale x 4 x float> @llvm.masked.load.nxv4f32.p0(ptr %gep.0.16, i32 1, <vscale x 4 x i1> %mask, <vscale x 4 x float> zeroinitializer)
%fmul = fmul <vscale x 4 x float> %load.0.0, %load.0.16
call void @llvm.masked.store.nxv4f32.p0(<vscale x 4 x float> %fmul, ptr %1, i32 1, <vscale x 4 x i1> %mask)
%load.1.0 = call <vscale x 4 x float> @llvm.masked.load.nxv4f32.p0(ptr %1, i32 1, <vscale x 4 x i1> %mask, <vscale x 4 x float> %passthrough)
ret <vscale x 4 x float> %load.1.0
}

define <vscale x 4 x float> @load_mask_differs(ptr %0, ptr %1, <vscale x 4 x float> %passthrough) {
; CHECK-LABEL: @load_mask_differs(
; CHECK-NEXT: [[MASK0:%.*]] = tail call <vscale x 4 x i1> @llvm.get.active.lane.mask.nxv4i1.i32(i32 0, i32 8)
; CHECK-NEXT: [[MASK1:%.*]] = tail call <vscale x 4 x i1> @llvm.get.active.lane.mask.nxv4i1.i32(i32 0, i32 4)
; CHECK-NEXT: [[LOAD_0_0:%.*]] = call <vscale x 4 x float> @llvm.masked.load.nxv4f32.p0(ptr [[TMP0:%.*]], i32 1, <vscale x 4 x i1> [[MASK0]], <vscale x 4 x float> zeroinitializer)
; CHECK-NEXT: [[GEP_0_16:%.*]] = getelementptr i8, ptr [[TMP0]], i32 16
; CHECK-NEXT: [[LOAD_0_16:%.*]] = call <vscale x 4 x float> @llvm.masked.load.nxv4f32.p0(ptr [[GEP_0_16]], i32 1, <vscale x 4 x i1> [[MASK0]], <vscale x 4 x float> zeroinitializer)
; CHECK-NEXT: [[FMUL:%.*]] = fmul <vscale x 4 x float> [[LOAD_0_0]], [[LOAD_0_16]]
; CHECK-NEXT: call void @llvm.masked.store.nxv4f32.p0(<vscale x 4 x float> [[FMUL]], ptr [[TMP1:%.*]], i32 1, <vscale x 4 x i1> [[MASK0]])
; CHECK-NEXT: [[LOAD_1_0:%.*]] = call <vscale x 4 x float> @llvm.masked.load.nxv4f32.p0(ptr [[TMP1]], i32 1, <vscale x 4 x i1> [[MASK1]], <vscale x 4 x float> [[PASSTHROUGH:%.*]])
; CHECK-NEXT: ret <vscale x 4 x float> [[LOAD_1_0]]
;
%mask0 = tail call <vscale x 4 x i1> @llvm.get.active.lane.mask.nxv4i1.i32(i32 0, i32 8)
%mask1 = tail call <vscale x 4 x i1> @llvm.get.active.lane.mask.nxv4i1.i32(i32 0, i32 4)
%load.0.0 = call <vscale x 4 x float> @llvm.masked.load.nxv4f32.p0(ptr %0, i32 1, <vscale x 4 x i1> %mask0, <vscale x 4 x float> zeroinitializer)
%gep.0.16 = getelementptr i8, ptr %0, i32 16
%load.0.16 = call <vscale x 4 x float> @llvm.masked.load.nxv4f32.p0(ptr %gep.0.16, i32 1, <vscale x 4 x i1> %mask0, <vscale x 4 x float> zeroinitializer)
%fmul = fmul <vscale x 4 x float> %load.0.0, %load.0.16
call void @llvm.masked.store.nxv4f32.p0(<vscale x 4 x float> %fmul, ptr %1, i32 1, <vscale x 4 x i1> %mask0)
%load.1.0 = call <vscale x 4 x float> @llvm.masked.load.nxv4f32.p0(ptr %1, i32 1, <vscale x 4 x i1> %mask1, <vscale x 4 x float> %passthrough)
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@david-arm david-arm Sep 29, 2025

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In theory, we could still remove the load because mask1 is a subset of mask0 and the pointer is the same. We'd just need to create a select based on mask1 and passthrough.

Again, doesn't have to be done in this patch!

ret <vscale x 4 x float> %load.1.0
}

define <vscale x 4 x float> @store_mask_differs(ptr %0, ptr %1, <vscale x 4 x float> %passthrough) {
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@david-arm david-arm Sep 29, 2025

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It seems to me the main difference between this test and the one above is that here there isn't any chance to optimise the final load because the size of the stored value is less than the loaded one due to mask1 being smaller than mask0.

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@MDevereau MDevereau Sep 29, 2025

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This was just to check that any mask if different in any way, even if one mask is a subset of another, gets rejected. Are you asking for any changes to either test?

; CHECK-LABEL: @store_mask_differs(
; CHECK-NEXT: [[MASK0:%.*]] = tail call <vscale x 4 x i1> @llvm.get.active.lane.mask.nxv4i1.i32(i32 0, i32 8)
; CHECK-NEXT: [[MASK1:%.*]] = tail call <vscale x 4 x i1> @llvm.get.active.lane.mask.nxv4i1.i32(i32 0, i32 4)
; CHECK-NEXT: [[LOAD_0_0:%.*]] = call <vscale x 4 x float> @llvm.masked.load.nxv4f32.p0(ptr [[TMP0:%.*]], i32 1, <vscale x 4 x i1> [[MASK0]], <vscale x 4 x float> zeroinitializer)
; CHECK-NEXT: [[GEP_0_16:%.*]] = getelementptr i8, ptr [[TMP0]], i32 16
; CHECK-NEXT: [[LOAD_0_16:%.*]] = call <vscale x 4 x float> @llvm.masked.load.nxv4f32.p0(ptr [[GEP_0_16]], i32 1, <vscale x 4 x i1> [[MASK0]], <vscale x 4 x float> zeroinitializer)
; CHECK-NEXT: [[FMUL:%.*]] = fmul <vscale x 4 x float> [[LOAD_0_0]], [[LOAD_0_16]]
; CHECK-NEXT: call void @llvm.masked.store.nxv4f32.p0(<vscale x 4 x float> [[FMUL]], ptr [[TMP1:%.*]], i32 1, <vscale x 4 x i1> [[MASK1]])
; CHECK-NEXT: [[LOAD_1_0:%.*]] = call <vscale x 4 x float> @llvm.masked.load.nxv4f32.p0(ptr [[TMP1]], i32 1, <vscale x 4 x i1> [[MASK0]], <vscale x 4 x float> [[PASSTHROUGH:%.*]])
; CHECK-NEXT: ret <vscale x 4 x float> [[LOAD_1_0]]
;
%mask0 = tail call <vscale x 4 x i1> @llvm.get.active.lane.mask.nxv4i1.i32(i32 0, i32 8)
%mask1 = tail call <vscale x 4 x i1> @llvm.get.active.lane.mask.nxv4i1.i32(i32 0, i32 4)
%load.0.0 = call <vscale x 4 x float> @llvm.masked.load.nxv4f32.p0(ptr %0, i32 1, <vscale x 4 x i1> %mask0, <vscale x 4 x float> zeroinitializer)
%gep.0.16 = getelementptr i8, ptr %0, i32 16
%load.0.16 = call <vscale x 4 x float> @llvm.masked.load.nxv4f32.p0(ptr %gep.0.16, i32 1, <vscale x 4 x i1> %mask0, <vscale x 4 x float> zeroinitializer)
%fmul = fmul <vscale x 4 x float> %load.0.0, %load.0.16
call void @llvm.masked.store.nxv4f32.p0(<vscale x 4 x float> %fmul, ptr %1, i32 1, <vscale x 4 x i1> %mask1)
%load.1.0 = call <vscale x 4 x float> @llvm.masked.load.nxv4f32.p0(ptr %1, i32 1, <vscale x 4 x i1> %mask0, <vscale x 4 x float> %passthrough)
ret <vscale x 4 x float> %load.1.0
}