[llvm-branch-commits] [llvm] [ConstantFolding] Add constant folding for mask.beforefirst (PR #234472)
Luke Lau via llvm-branch-commits
llvm-branch-commits at lists.llvm.org
Fri Oct 23 02:04:16 PDT 2026
https://github.com/lukel97 updated https://github.com/llvm/llvm-project/pull/234472
>From eedf622840d126641b86804d57ebd3571a17254a Mon Sep 17 00:00:00 2001
From: Luke Lau <luke at igalia.com>
Date: Thu, 22 Oct 2026 10:34:13 +0800
Subject: [PATCH 1/4] Precommit tests
---
.../ConstProp/mask-beforefirst.ll | 74 +++++++++++++++++++
1 file changed, 74 insertions(+)
create mode 100644 llvm/test/Transforms/InstSimplify/ConstProp/mask-beforefirst.ll
diff --git a/llvm/test/Transforms/InstSimplify/ConstProp/mask-beforefirst.ll b/llvm/test/Transforms/InstSimplify/ConstProp/mask-beforefirst.ll
new file mode 100644
index 00000000000000..dd88f618a0b356
--- /dev/null
+++ b/llvm/test/Transforms/InstSimplify/ConstProp/mask-beforefirst.ll
@@ -0,0 +1,74 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 6
+; RUN: opt -p instsimplify -S < %s | FileCheck %s
+
+define <4 x i1> @v4i1_zero() {
+; CHECK-LABEL: define <4 x i1> @v4i1_zero() {
+; CHECK-NEXT: [[RES:%.*]] = call <4 x i1> @llvm.mask.beforefirst.v4i1(<4 x i1> zeroinitializer)
+; CHECK-NEXT: ret <4 x i1> [[RES]]
+;
+ %res = call <4 x i1> @llvm.mask.beforefirst(<4 x i1> zeroinitializer)
+ ret <4 x i1> %res
+}
+
+define <4 x i1> @v4i1_ones() {
+; CHECK-LABEL: define <4 x i1> @v4i1_ones() {
+; CHECK-NEXT: [[RES:%.*]] = call <4 x i1> @llvm.mask.beforefirst.v4i1(<4 x i1> splat (i1 true))
+; CHECK-NEXT: ret <4 x i1> [[RES]]
+;
+ %res = call <4 x i1> @llvm.mask.beforefirst(<4 x i1> splat (i1 true))
+ ret <4 x i1> %res
+}
+
+define <4 x i1> @v4i1() {
+; CHECK-LABEL: define <4 x i1> @v4i1() {
+; CHECK-NEXT: [[RES:%.*]] = call <4 x i1> @llvm.mask.beforefirst.v4i1(<4 x i1> <i1 false, i1 true, i1 false, i1 true>)
+; CHECK-NEXT: ret <4 x i1> [[RES]]
+;
+ %res = call <4 x i1> @llvm.mask.beforefirst(<4 x i1> <i1 false, i1 true, i1 false, i1 true>)
+ ret <4 x i1> %res
+}
+
+define <4 x i1> @v4i1_undef() {
+; CHECK-LABEL: define <4 x i1> @v4i1_undef() {
+; CHECK-NEXT: [[RES:%.*]] = call <4 x i1> @llvm.mask.beforefirst.v4i1(<4 x i1> <i1 undef, i1 true, i1 false, i1 false>)
+; CHECK-NEXT: ret <4 x i1> [[RES]]
+;
+ %res = call <4 x i1> @llvm.mask.beforefirst(<4 x i1> <i1 undef, i1 true, i1 false, i1 false>)
+ ret <4 x i1> %res
+}
+
+define <4 x i1> @v4i1_poison() {
+; CHECK-LABEL: define <4 x i1> @v4i1_poison() {
+; CHECK-NEXT: [[RES:%.*]] = call <4 x i1> @llvm.mask.beforefirst.v4i1(<4 x i1> <i1 false, i1 true, i1 poison, i1 false>)
+; CHECK-NEXT: ret <4 x i1> [[RES]]
+;
+ %res = call <4 x i1> @llvm.mask.beforefirst(<4 x i1> <i1 false, i1 true, i1 poison, i1 false>)
+ ret <4 x i1> %res
+}
+
+define <vscale x 4 x i1> @nxv4i1_zero() {
+; CHECK-LABEL: define <vscale x 4 x i1> @nxv4i1_zero() {
+; CHECK-NEXT: [[RES:%.*]] = call <vscale x 4 x i1> @llvm.mask.beforefirst.nxv4i1(<vscale x 4 x i1> zeroinitializer)
+; CHECK-NEXT: ret <vscale x 4 x i1> [[RES]]
+;
+ %res = call <vscale x 4 x i1> @llvm.mask.beforefirst(<vscale x 4 x i1> zeroinitializer)
+ ret <vscale x 4 x i1> %res
+}
+
+define <vscale x 4 x i1> @nxv4i1_ones() {
+; CHECK-LABEL: define <vscale x 4 x i1> @nxv4i1_ones() {
+; CHECK-NEXT: [[RES:%.*]] = call <vscale x 4 x i1> @llvm.mask.beforefirst.nxv4i1(<vscale x 4 x i1> splat (i1 true))
+; CHECK-NEXT: ret <vscale x 4 x i1> [[RES]]
+;
+ %res = call <vscale x 4 x i1> @llvm.mask.beforefirst(<vscale x 4 x i1> splat (i1 true))
+ ret <vscale x 4 x i1> %res
+}
+
+define <vscale x 4 x i1> @nxv4i1_poison() {
+; CHECK-LABEL: define <vscale x 4 x i1> @nxv4i1_poison() {
+; CHECK-NEXT: [[RES:%.*]] = call <vscale x 4 x i1> @llvm.mask.beforefirst.nxv4i1(<vscale x 4 x i1> poison)
+; CHECK-NEXT: ret <vscale x 4 x i1> [[RES]]
+;
+ %res = call <vscale x 4 x i1> @llvm.mask.beforefirst(<vscale x 4 x i1> poison)
+ ret <vscale x 4 x i1> %res
+}
>From 4fea4b46abeb27c368c3116e65f3da46199199a7 Mon Sep 17 00:00:00 2001
From: Luke Lau <luke at igalia.com>
Date: Thu, 22 Oct 2026 10:35:48 +0800
Subject: [PATCH 2/4] [ConstantFolding] Add constant folding for
mask.beforefirst
Poison lanes poison the entire result, and undef elements are ignored
Assisted-by: Opus 5.5
---
llvm/lib/Analysis/ConstantFolding.cpp | 23 ++++++++++++++++++
.../ConstProp/mask-beforefirst.ll | 24 +++++++------------
2 files changed, 31 insertions(+), 16 deletions(-)
diff --git a/llvm/lib/Analysis/ConstantFolding.cpp b/llvm/lib/Analysis/ConstantFolding.cpp
index 5169450936dc36..3219248a99e5dd 100644
--- a/llvm/lib/Analysis/ConstantFolding.cpp
+++ b/llvm/lib/Analysis/ConstantFolding.cpp
@@ -1837,6 +1837,7 @@ static bool canConstantFoldIntrinsic(Intrinsic::ID ID, bool IsStrictFP) {
case Intrinsic::launder_invariant_group:
case Intrinsic::masked_load:
case Intrinsic::get_active_lane_mask:
+ case Intrinsic::mask_beforefirst:
case Intrinsic::abs:
case Intrinsic::smax:
case Intrinsic::smin:
@@ -4551,6 +4552,20 @@ static Constant *ConstantFoldFixedVectorCall(
}
return nullptr;
}
+ case Intrinsic::mask_beforefirst: {
+ bool SeenActive = false;
+ for (unsigned I = 0, E = FVTy->getNumElements(); I != E; ++I) {
+ Constant *Elt = Operands[0]->getAggregateElement(I);
+ if (isa_and_nonnull<PoisonValue>(Elt))
+ return PoisonValue::get(FVTy);
+ if (auto *CI = dyn_cast_or_null<ConstantInt>(Elt))
+ SeenActive |= CI->isOne();
+ else if (!isa_and_nonnull<UndefValue>(Elt))
+ return nullptr;
+ Result[I] = ConstantInt::getBool(Ty, !SeenActive);
+ }
+ return ConstantVector::get(Result);
+ }
case Intrinsic::vector_extract: {
auto *Idx = dyn_cast<ConstantInt>(Operands[1]);
Constant *Vec = Operands[0];
@@ -4711,6 +4726,14 @@ static Constant *ConstantFoldScalableVectorCall(
return ConstantVector::getNullValue(SVTy);
break;
}
+ case Intrinsic::mask_beforefirst: {
+ Constant *SplatVal = Operands[0]->getSplatValue();
+ if (isa_and_nonnull<PoisonValue>(SplatVal))
+ return PoisonValue::get(SVTy);
+ if (auto *CI = dyn_cast_if_present<ConstantInt>(SplatVal))
+ return ConstantInt::getBool(SVTy, CI->isZero());
+ break;
+ }
case Intrinsic::vector_interleave2:
case Intrinsic::vector_interleave3:
case Intrinsic::vector_interleave4:
diff --git a/llvm/test/Transforms/InstSimplify/ConstProp/mask-beforefirst.ll b/llvm/test/Transforms/InstSimplify/ConstProp/mask-beforefirst.ll
index dd88f618a0b356..24c8fbdcbff680 100644
--- a/llvm/test/Transforms/InstSimplify/ConstProp/mask-beforefirst.ll
+++ b/llvm/test/Transforms/InstSimplify/ConstProp/mask-beforefirst.ll
@@ -3,8 +3,7 @@
define <4 x i1> @v4i1_zero() {
; CHECK-LABEL: define <4 x i1> @v4i1_zero() {
-; CHECK-NEXT: [[RES:%.*]] = call <4 x i1> @llvm.mask.beforefirst.v4i1(<4 x i1> zeroinitializer)
-; CHECK-NEXT: ret <4 x i1> [[RES]]
+; CHECK-NEXT: ret <4 x i1> splat (i1 true)
;
%res = call <4 x i1> @llvm.mask.beforefirst(<4 x i1> zeroinitializer)
ret <4 x i1> %res
@@ -12,8 +11,7 @@ define <4 x i1> @v4i1_zero() {
define <4 x i1> @v4i1_ones() {
; CHECK-LABEL: define <4 x i1> @v4i1_ones() {
-; CHECK-NEXT: [[RES:%.*]] = call <4 x i1> @llvm.mask.beforefirst.v4i1(<4 x i1> splat (i1 true))
-; CHECK-NEXT: ret <4 x i1> [[RES]]
+; CHECK-NEXT: ret <4 x i1> zeroinitializer
;
%res = call <4 x i1> @llvm.mask.beforefirst(<4 x i1> splat (i1 true))
ret <4 x i1> %res
@@ -21,8 +19,7 @@ define <4 x i1> @v4i1_ones() {
define <4 x i1> @v4i1() {
; CHECK-LABEL: define <4 x i1> @v4i1() {
-; CHECK-NEXT: [[RES:%.*]] = call <4 x i1> @llvm.mask.beforefirst.v4i1(<4 x i1> <i1 false, i1 true, i1 false, i1 true>)
-; CHECK-NEXT: ret <4 x i1> [[RES]]
+; CHECK-NEXT: ret <4 x i1> <i1 true, i1 false, i1 false, i1 false>
;
%res = call <4 x i1> @llvm.mask.beforefirst(<4 x i1> <i1 false, i1 true, i1 false, i1 true>)
ret <4 x i1> %res
@@ -30,8 +27,7 @@ define <4 x i1> @v4i1() {
define <4 x i1> @v4i1_undef() {
; CHECK-LABEL: define <4 x i1> @v4i1_undef() {
-; CHECK-NEXT: [[RES:%.*]] = call <4 x i1> @llvm.mask.beforefirst.v4i1(<4 x i1> <i1 undef, i1 true, i1 false, i1 false>)
-; CHECK-NEXT: ret <4 x i1> [[RES]]
+; CHECK-NEXT: ret <4 x i1> <i1 true, i1 false, i1 false, i1 false>
;
%res = call <4 x i1> @llvm.mask.beforefirst(<4 x i1> <i1 undef, i1 true, i1 false, i1 false>)
ret <4 x i1> %res
@@ -39,8 +35,7 @@ define <4 x i1> @v4i1_undef() {
define <4 x i1> @v4i1_poison() {
; CHECK-LABEL: define <4 x i1> @v4i1_poison() {
-; CHECK-NEXT: [[RES:%.*]] = call <4 x i1> @llvm.mask.beforefirst.v4i1(<4 x i1> <i1 false, i1 true, i1 poison, i1 false>)
-; CHECK-NEXT: ret <4 x i1> [[RES]]
+; CHECK-NEXT: ret <4 x i1> poison
;
%res = call <4 x i1> @llvm.mask.beforefirst(<4 x i1> <i1 false, i1 true, i1 poison, i1 false>)
ret <4 x i1> %res
@@ -48,8 +43,7 @@ define <4 x i1> @v4i1_poison() {
define <vscale x 4 x i1> @nxv4i1_zero() {
; CHECK-LABEL: define <vscale x 4 x i1> @nxv4i1_zero() {
-; CHECK-NEXT: [[RES:%.*]] = call <vscale x 4 x i1> @llvm.mask.beforefirst.nxv4i1(<vscale x 4 x i1> zeroinitializer)
-; CHECK-NEXT: ret <vscale x 4 x i1> [[RES]]
+; CHECK-NEXT: ret <vscale x 4 x i1> splat (i1 true)
;
%res = call <vscale x 4 x i1> @llvm.mask.beforefirst(<vscale x 4 x i1> zeroinitializer)
ret <vscale x 4 x i1> %res
@@ -57,8 +51,7 @@ define <vscale x 4 x i1> @nxv4i1_zero() {
define <vscale x 4 x i1> @nxv4i1_ones() {
; CHECK-LABEL: define <vscale x 4 x i1> @nxv4i1_ones() {
-; CHECK-NEXT: [[RES:%.*]] = call <vscale x 4 x i1> @llvm.mask.beforefirst.nxv4i1(<vscale x 4 x i1> splat (i1 true))
-; CHECK-NEXT: ret <vscale x 4 x i1> [[RES]]
+; CHECK-NEXT: ret <vscale x 4 x i1> zeroinitializer
;
%res = call <vscale x 4 x i1> @llvm.mask.beforefirst(<vscale x 4 x i1> splat (i1 true))
ret <vscale x 4 x i1> %res
@@ -66,8 +59,7 @@ define <vscale x 4 x i1> @nxv4i1_ones() {
define <vscale x 4 x i1> @nxv4i1_poison() {
; CHECK-LABEL: define <vscale x 4 x i1> @nxv4i1_poison() {
-; CHECK-NEXT: [[RES:%.*]] = call <vscale x 4 x i1> @llvm.mask.beforefirst.nxv4i1(<vscale x 4 x i1> poison)
-; CHECK-NEXT: ret <vscale x 4 x i1> [[RES]]
+; CHECK-NEXT: ret <vscale x 4 x i1> poison
;
%res = call <vscale x 4 x i1> @llvm.mask.beforefirst(<vscale x 4 x i1> poison)
ret <vscale x 4 x i1> %res
>From 697541322856dd3e165f0a4f6a5c97fcb2852678 Mon Sep 17 00:00:00 2001
From: Luke Lau <luke at igalia.com>
Date: Thu, 22 Oct 2026 16:27:56 +0800
Subject: [PATCH 3/4] Remove undef handling
---
llvm/lib/Analysis/ConstantFolding.cpp | 6 +++---
.../Transforms/InstSimplify/ConstProp/mask-beforefirst.ll | 8 --------
2 files changed, 3 insertions(+), 11 deletions(-)
diff --git a/llvm/lib/Analysis/ConstantFolding.cpp b/llvm/lib/Analysis/ConstantFolding.cpp
index 3219248a99e5dd..a0c5357f72a46d 100644
--- a/llvm/lib/Analysis/ConstantFolding.cpp
+++ b/llvm/lib/Analysis/ConstantFolding.cpp
@@ -4558,10 +4558,10 @@ static Constant *ConstantFoldFixedVectorCall(
Constant *Elt = Operands[0]->getAggregateElement(I);
if (isa_and_nonnull<PoisonValue>(Elt))
return PoisonValue::get(FVTy);
- if (auto *CI = dyn_cast_or_null<ConstantInt>(Elt))
- SeenActive |= CI->isOne();
- else if (!isa_and_nonnull<UndefValue>(Elt))
+ auto *CI = dyn_cast_or_null<ConstantInt>(Elt);
+ if (!CI)
return nullptr;
+ SeenActive |= CI->isOne();
Result[I] = ConstantInt::getBool(Ty, !SeenActive);
}
return ConstantVector::get(Result);
diff --git a/llvm/test/Transforms/InstSimplify/ConstProp/mask-beforefirst.ll b/llvm/test/Transforms/InstSimplify/ConstProp/mask-beforefirst.ll
index 24c8fbdcbff680..8033be0bc02d98 100644
--- a/llvm/test/Transforms/InstSimplify/ConstProp/mask-beforefirst.ll
+++ b/llvm/test/Transforms/InstSimplify/ConstProp/mask-beforefirst.ll
@@ -25,14 +25,6 @@ define <4 x i1> @v4i1() {
ret <4 x i1> %res
}
-define <4 x i1> @v4i1_undef() {
-; CHECK-LABEL: define <4 x i1> @v4i1_undef() {
-; CHECK-NEXT: ret <4 x i1> <i1 true, i1 false, i1 false, i1 false>
-;
- %res = call <4 x i1> @llvm.mask.beforefirst(<4 x i1> <i1 undef, i1 true, i1 false, i1 false>)
- ret <4 x i1> %res
-}
-
define <4 x i1> @v4i1_poison() {
; CHECK-LABEL: define <4 x i1> @v4i1_poison() {
; CHECK-NEXT: ret <4 x i1> poison
>From eb95af82f5329a11ec2d5206a6631cc776959496 Mon Sep 17 00:00:00 2001
From: Luke Lau <luke at igalia.com>
Date: Thu, 22 Oct 2026 23:30:57 +0800
Subject: [PATCH 4/4] Address review comments
---
llvm/lib/Analysis/ConstantFolding.cpp | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/llvm/lib/Analysis/ConstantFolding.cpp b/llvm/lib/Analysis/ConstantFolding.cpp
index a0c5357f72a46d..069809a16545ef 100644
--- a/llvm/lib/Analysis/ConstantFolding.cpp
+++ b/llvm/lib/Analysis/ConstantFolding.cpp
@@ -4553,7 +4553,9 @@ static Constant *ConstantFoldFixedVectorCall(
return nullptr;
}
case Intrinsic::mask_beforefirst: {
- bool SeenActive = false;
+ Constant *True = ConstantInt::getTrue(Ty);
+ Constant *False = ConstantInt::getFalse(Ty);
+ Constant *Current = True;
for (unsigned I = 0, E = FVTy->getNumElements(); I != E; ++I) {
Constant *Elt = Operands[0]->getAggregateElement(I);
if (isa_and_nonnull<PoisonValue>(Elt))
@@ -4561,8 +4563,9 @@ static Constant *ConstantFoldFixedVectorCall(
auto *CI = dyn_cast_or_null<ConstantInt>(Elt);
if (!CI)
return nullptr;
- SeenActive |= CI->isOne();
- Result[I] = ConstantInt::getBool(Ty, !SeenActive);
+ if (CI->isOne())
+ Current = False;
+ Result[I] = Current;
}
return ConstantVector::get(Result);
}
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