[llvm] [SCCP] Handle llvm.experimental.get.vector.length calls (PR #169527)
Luke Lau via llvm-commits
llvm-commits at lists.llvm.org
Mon Dec 1 01:57:20 PST 2025
https://github.com/lukel97 updated https://github.com/llvm/llvm-project/pull/169527
>From 732969a3a328499c349eb7c750a8a520410b5ec6 Mon Sep 17 00:00:00 2001
From: Luke Lau <luke at igalia.com>
Date: Wed, 26 Nov 2025 01:09:38 +0800
Subject: [PATCH 1/3] Precommit tests
---
.../SCCP/get_vector_length-intrinsic.ll | 148 ++++++++++++++++++
1 file changed, 148 insertions(+)
create mode 100644 llvm/test/Transforms/SCCP/get_vector_length-intrinsic.ll
diff --git a/llvm/test/Transforms/SCCP/get_vector_length-intrinsic.ll b/llvm/test/Transforms/SCCP/get_vector_length-intrinsic.ll
new file mode 100644
index 0000000000000..2e2d3ac82106a
--- /dev/null
+++ b/llvm/test/Transforms/SCCP/get_vector_length-intrinsic.ll
@@ -0,0 +1,148 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 6
+; RUN: opt < %s -p sccp -S | FileCheck %s
+
+define i1 @result_le_count() {
+; CHECK-LABEL: define i1 @result_le_count() {
+; CHECK-NEXT: [[X:%.*]] = call i32 @llvm.experimental.get.vector.length.i32(i32 3, i32 4, i1 false)
+; CHECK-NEXT: [[RES:%.*]] = icmp ule i32 [[X]], 3
+; CHECK-NEXT: ret i1 [[RES]]
+;
+ %x = call i32 @llvm.experimental.get.vector.length(i32 3, i32 4, i1 false)
+ %res = icmp ule i32 %x, 3
+ ret i1 %res
+}
+
+define i1 @result_le_max_lanes(i32 %count) {
+; CHECK-LABEL: define i1 @result_le_max_lanes(
+; CHECK-SAME: i32 [[COUNT:%.*]]) {
+; CHECK-NEXT: [[X:%.*]] = call i32 @llvm.experimental.get.vector.length.i32(i32 [[COUNT]], i32 3, i1 false)
+; CHECK-NEXT: [[RES:%.*]] = icmp ule i32 [[X]], 3
+; CHECK-NEXT: ret i1 [[RES]]
+;
+ %x = call i32 @llvm.experimental.get.vector.length(i32 %count, i32 3, i1 false)
+ %res = icmp ule i32 %x, 3
+ ret i1 %res
+}
+
+define i1 @result_le_max_lanes_scalable(i32 %count) vscale_range(2, 4) {
+; CHECK-LABEL: define i1 @result_le_max_lanes_scalable(
+; CHECK-SAME: i32 [[COUNT:%.*]]) #[[ATTR0:[0-9]+]] {
+; CHECK-NEXT: [[X:%.*]] = call i32 @llvm.experimental.get.vector.length.i32(i32 [[COUNT]], i32 4, i1 true)
+; CHECK-NEXT: [[RES:%.*]] = icmp ule i32 [[X]], 16
+; CHECK-NEXT: ret i1 [[RES]]
+;
+ %x = call i32 @llvm.experimental.get.vector.length(i32 %count, i32 4, i1 true)
+ %res = icmp ule i32 %x, 16
+ ret i1 %res
+}
+
+define i32 @count_le_max_lanes() {
+; CHECK-LABEL: define i32 @count_le_max_lanes() {
+; CHECK-NEXT: [[ENTRY:.*]]:
+; CHECK-NEXT: br label %[[LOOP:.*]]
+; CHECK: [[LOOP]]:
+; CHECK-NEXT: [[IV:%.*]] = phi i32 [ 4, %[[ENTRY]] ], [ [[IV_NEXT:%.*]], %[[LOOP]] ]
+; CHECK-NEXT: [[X:%.*]] = call i32 @llvm.experimental.get.vector.length.i32(i32 [[IV]], i32 4, i1 false)
+; CHECK-NEXT: [[IV_NEXT]] = sub i32 [[IV]], [[X]]
+; CHECK-NEXT: [[EC:%.*]] = icmp eq i32 [[IV_NEXT]], 0
+; CHECK-NEXT: br i1 [[EC]], label %[[EXIT:.*]], label %[[LOOP]]
+; CHECK: [[EXIT]]:
+; CHECK-NEXT: ret i32 [[X]]
+;
+entry:
+ br label %loop
+
+loop:
+ %iv = phi i32 [4, %entry], [%iv.next, %loop]
+ %x = call i32 @llvm.experimental.get.vector.length(i32 %iv, i32 4, i1 false)
+ %iv.next = sub i32 %iv, %x
+ %ec = icmp eq i32 %iv.next, 0
+ br i1 %ec, label %exit, label %loop
+
+exit:
+ ret i32 %x
+}
+
+; Can't simplify because %iv isn't <= max lanes.
+define i32 @count_not_le_max_lanes() {
+; CHECK-LABEL: define i32 @count_not_le_max_lanes() {
+; CHECK-NEXT: [[ENTRY:.*]]:
+; CHECK-NEXT: br label %[[LOOP:.*]]
+; CHECK: [[LOOP]]:
+; CHECK-NEXT: [[IV:%.*]] = phi i32 [ 6, %[[ENTRY]] ], [ [[IV_NEXT:%.*]], %[[LOOP]] ]
+; CHECK-NEXT: [[X:%.*]] = call i32 @llvm.experimental.get.vector.length.i32(i32 [[IV]], i32 4, i1 false)
+; CHECK-NEXT: [[IV_NEXT]] = sub i32 [[IV]], [[X]]
+; CHECK-NEXT: [[EC:%.*]] = icmp eq i32 [[IV_NEXT]], 0
+; CHECK-NEXT: br i1 [[EC]], label %[[EXIT:.*]], label %[[LOOP]]
+; CHECK: [[EXIT]]:
+; CHECK-NEXT: ret i32 [[X]]
+;
+entry:
+ br label %loop
+
+loop:
+ %iv = phi i32 [6, %entry], [%iv.next, %loop]
+ %x = call i32 @llvm.experimental.get.vector.length(i32 %iv, i32 4, i1 false)
+ %iv.next = sub i32 %iv, %x
+ %ec = icmp eq i32 %iv.next, 0
+ br i1 %ec, label %exit, label %loop
+
+exit:
+ ret i32 %x
+}
+
+define i32 @count_le_max_lanes_scalable_known() vscale_range(4, 8) {
+; CHECK-LABEL: define i32 @count_le_max_lanes_scalable_known(
+; CHECK-SAME: ) #[[ATTR1:[0-9]+]] {
+; CHECK-NEXT: [[ENTRY:.*]]:
+; CHECK-NEXT: br label %[[LOOP:.*]]
+; CHECK: [[LOOP]]:
+; CHECK-NEXT: [[IV:%.*]] = phi i32 [ 16, %[[ENTRY]] ], [ [[IV_NEXT:%.*]], %[[LOOP]] ]
+; CHECK-NEXT: [[X:%.*]] = call i32 @llvm.experimental.get.vector.length.i32(i32 [[IV]], i32 4, i1 true)
+; CHECK-NEXT: [[IV_NEXT]] = sub i32 [[IV]], [[X]]
+; CHECK-NEXT: [[EC:%.*]] = icmp eq i32 [[IV_NEXT]], 0
+; CHECK-NEXT: br i1 [[EC]], label %[[EXIT:.*]], label %[[LOOP]]
+; CHECK: [[EXIT]]:
+; CHECK-NEXT: ret i32 [[X]]
+;
+entry:
+ br label %loop
+
+loop:
+ %iv = phi i32 [16, %entry], [%iv.next, %loop]
+ %x = call i32 @llvm.experimental.get.vector.length(i32 %iv, i32 4, i1 true)
+ %iv.next = sub i32 %iv, %x
+ %ec = icmp eq i32 %iv.next, 0
+ br i1 %ec, label %exit, label %loop
+
+exit:
+ ret i32 %x
+}
+
+; Can't simplify because %iv isn't guaranteed <= max lanes.
+define i32 @count_le_max_lanes_scalable_unknown() {
+; CHECK-LABEL: define i32 @count_le_max_lanes_scalable_unknown() {
+; CHECK-NEXT: [[ENTRY:.*]]:
+; CHECK-NEXT: br label %[[LOOP:.*]]
+; CHECK: [[LOOP]]:
+; CHECK-NEXT: [[IV:%.*]] = phi i32 [ 16, %[[ENTRY]] ], [ [[IV_NEXT:%.*]], %[[LOOP]] ]
+; CHECK-NEXT: [[X:%.*]] = call i32 @llvm.experimental.get.vector.length.i32(i32 [[IV]], i32 4, i1 true)
+; CHECK-NEXT: [[IV_NEXT]] = sub i32 [[IV]], [[X]]
+; CHECK-NEXT: [[EC:%.*]] = icmp eq i32 [[IV_NEXT]], 0
+; CHECK-NEXT: br i1 [[EC]], label %[[EXIT:.*]], label %[[LOOP]]
+; CHECK: [[EXIT]]:
+; CHECK-NEXT: ret i32 [[X]]
+;
+entry:
+ br label %loop
+
+loop:
+ %iv = phi i32 [16, %entry], [%iv.next, %loop]
+ %x = call i32 @llvm.experimental.get.vector.length(i32 %iv, i32 4, i1 true)
+ %iv.next = sub i32 %iv, %x
+ %ec = icmp eq i32 %iv.next, 0
+ br i1 %ec, label %exit, label %loop
+
+exit:
+ ret i32 %x
+}
>From 0fa4cb6a618a02e1d3463e9d3dfae34cde7c29c5 Mon Sep 17 00:00:00 2001
From: Luke Lau <luke at igalia.com>
Date: Wed, 26 Nov 2025 01:11:10 +0800
Subject: [PATCH 2/3] [SCCP] Handle llvm.experimental.get.vector.length calls
---
llvm/lib/Transforms/Utils/SCCPSolver.cpp | 26 ++++++++++++++
.../SCCP/get_vector_length-intrinsic.ll | 34 ++++++-------------
2 files changed, 37 insertions(+), 23 deletions(-)
diff --git a/llvm/lib/Transforms/Utils/SCCPSolver.cpp b/llvm/lib/Transforms/Utils/SCCPSolver.cpp
index 4947d03a2dc66..7a5cc289fa5c9 100644
--- a/llvm/lib/Transforms/Utils/SCCPSolver.cpp
+++ b/llvm/lib/Transforms/Utils/SCCPSolver.cpp
@@ -2098,6 +2098,32 @@ void SCCPInstVisitor::handleCallResult(CallBase &CB) {
return (void)mergeInValue(ValueState[II], II,
ValueLatticeElement::getRange(Result));
}
+ if (II->getIntrinsicID() == Intrinsic::experimental_get_vector_length) {
+ unsigned BitWidth = CB.getType()->getScalarSizeInBits();
+ Value *CountArg = II->getArgOperand(0);
+ Value *VF = II->getArgOperand(1);
+ bool Scalable = cast<ConstantInt>(II->getArgOperand(2))->isOne();
+ ConstantRange Count = getValueState(CountArg)
+ .asConstantRange(CountArg->getType(), false)
+ .zextOrTrunc(BitWidth);
+ ConstantRange MaxLanes =
+ getValueState(VF).asConstantRange(BitWidth, false);
+ if (Scalable)
+ MaxLanes =
+ MaxLanes.multiply(getVScaleRange(II->getFunction(), BitWidth));
+
+ // The result is always less than both Count and MaxLanes.
+ ConstantRange Result(
+ APInt::getZero(BitWidth),
+ APIntOps::umin(Count.getUpper(), MaxLanes.getUpper()));
+
+ // If Count <= MaxLanes, getvectorlength(Count, MaxLanes) = Count
+ if (Count.icmp(CmpInst::ICMP_ULE, MaxLanes))
+ Result = Count;
+
+ return (void)mergeInValue(ValueState[II], II,
+ ValueLatticeElement::getRange(Result));
+ }
if (ConstantRange::isIntrinsicSupported(II->getIntrinsicID())) {
// Compute result range for intrinsics supported by ConstantRange.
diff --git a/llvm/test/Transforms/SCCP/get_vector_length-intrinsic.ll b/llvm/test/Transforms/SCCP/get_vector_length-intrinsic.ll
index 2e2d3ac82106a..3cb6154447631 100644
--- a/llvm/test/Transforms/SCCP/get_vector_length-intrinsic.ll
+++ b/llvm/test/Transforms/SCCP/get_vector_length-intrinsic.ll
@@ -3,9 +3,7 @@
define i1 @result_le_count() {
; CHECK-LABEL: define i1 @result_le_count() {
-; CHECK-NEXT: [[X:%.*]] = call i32 @llvm.experimental.get.vector.length.i32(i32 3, i32 4, i1 false)
-; CHECK-NEXT: [[RES:%.*]] = icmp ule i32 [[X]], 3
-; CHECK-NEXT: ret i1 [[RES]]
+; CHECK-NEXT: ret i1 true
;
%x = call i32 @llvm.experimental.get.vector.length(i32 3, i32 4, i1 false)
%res = icmp ule i32 %x, 3
@@ -16,8 +14,7 @@ define i1 @result_le_max_lanes(i32 %count) {
; CHECK-LABEL: define i1 @result_le_max_lanes(
; CHECK-SAME: i32 [[COUNT:%.*]]) {
; CHECK-NEXT: [[X:%.*]] = call i32 @llvm.experimental.get.vector.length.i32(i32 [[COUNT]], i32 3, i1 false)
-; CHECK-NEXT: [[RES:%.*]] = icmp ule i32 [[X]], 3
-; CHECK-NEXT: ret i1 [[RES]]
+; CHECK-NEXT: ret i1 true
;
%x = call i32 @llvm.experimental.get.vector.length(i32 %count, i32 3, i1 false)
%res = icmp ule i32 %x, 3
@@ -28,8 +25,7 @@ define i1 @result_le_max_lanes_scalable(i32 %count) vscale_range(2, 4) {
; CHECK-LABEL: define i1 @result_le_max_lanes_scalable(
; CHECK-SAME: i32 [[COUNT:%.*]]) #[[ATTR0:[0-9]+]] {
; CHECK-NEXT: [[X:%.*]] = call i32 @llvm.experimental.get.vector.length.i32(i32 [[COUNT]], i32 4, i1 true)
-; CHECK-NEXT: [[RES:%.*]] = icmp ule i32 [[X]], 16
-; CHECK-NEXT: ret i1 [[RES]]
+; CHECK-NEXT: ret i1 true
;
%x = call i32 @llvm.experimental.get.vector.length(i32 %count, i32 4, i1 true)
%res = icmp ule i32 %x, 16
@@ -38,16 +34,12 @@ define i1 @result_le_max_lanes_scalable(i32 %count) vscale_range(2, 4) {
define i32 @count_le_max_lanes() {
; CHECK-LABEL: define i32 @count_le_max_lanes() {
-; CHECK-NEXT: [[ENTRY:.*]]:
+; CHECK-NEXT: [[ENTRY:.*:]]
; CHECK-NEXT: br label %[[LOOP:.*]]
; CHECK: [[LOOP]]:
-; CHECK-NEXT: [[IV:%.*]] = phi i32 [ 4, %[[ENTRY]] ], [ [[IV_NEXT:%.*]], %[[LOOP]] ]
-; CHECK-NEXT: [[X:%.*]] = call i32 @llvm.experimental.get.vector.length.i32(i32 [[IV]], i32 4, i1 false)
-; CHECK-NEXT: [[IV_NEXT]] = sub i32 [[IV]], [[X]]
-; CHECK-NEXT: [[EC:%.*]] = icmp eq i32 [[IV_NEXT]], 0
-; CHECK-NEXT: br i1 [[EC]], label %[[EXIT:.*]], label %[[LOOP]]
+; CHECK-NEXT: br label %[[EXIT:.*]]
; CHECK: [[EXIT]]:
-; CHECK-NEXT: ret i32 [[X]]
+; CHECK-NEXT: ret i32 4
;
entry:
br label %loop
@@ -65,7 +57,7 @@ exit:
; Can't simplify because %iv isn't <= max lanes.
define i32 @count_not_le_max_lanes() {
-; CHECK-LABEL: define i32 @count_not_le_max_lanes() {
+; CHECK-LABEL: define range(i32 0, 5) i32 @count_not_le_max_lanes() {
; CHECK-NEXT: [[ENTRY:.*]]:
; CHECK-NEXT: br label %[[LOOP:.*]]
; CHECK: [[LOOP]]:
@@ -94,16 +86,12 @@ exit:
define i32 @count_le_max_lanes_scalable_known() vscale_range(4, 8) {
; CHECK-LABEL: define i32 @count_le_max_lanes_scalable_known(
; CHECK-SAME: ) #[[ATTR1:[0-9]+]] {
-; CHECK-NEXT: [[ENTRY:.*]]:
+; CHECK-NEXT: [[ENTRY:.*:]]
; CHECK-NEXT: br label %[[LOOP:.*]]
; CHECK: [[LOOP]]:
-; CHECK-NEXT: [[IV:%.*]] = phi i32 [ 16, %[[ENTRY]] ], [ [[IV_NEXT:%.*]], %[[LOOP]] ]
-; CHECK-NEXT: [[X:%.*]] = call i32 @llvm.experimental.get.vector.length.i32(i32 [[IV]], i32 4, i1 true)
-; CHECK-NEXT: [[IV_NEXT]] = sub i32 [[IV]], [[X]]
-; CHECK-NEXT: [[EC:%.*]] = icmp eq i32 [[IV_NEXT]], 0
-; CHECK-NEXT: br i1 [[EC]], label %[[EXIT:.*]], label %[[LOOP]]
+; CHECK-NEXT: br label %[[EXIT:.*]]
; CHECK: [[EXIT]]:
-; CHECK-NEXT: ret i32 [[X]]
+; CHECK-NEXT: ret i32 16
;
entry:
br label %loop
@@ -121,7 +109,7 @@ exit:
; Can't simplify because %iv isn't guaranteed <= max lanes.
define i32 @count_le_max_lanes_scalable_unknown() {
-; CHECK-LABEL: define i32 @count_le_max_lanes_scalable_unknown() {
+; CHECK-LABEL: define range(i32 0, -1) i32 @count_le_max_lanes_scalable_unknown() {
; CHECK-NEXT: [[ENTRY:.*]]:
; CHECK-NEXT: br label %[[LOOP:.*]]
; CHECK: [[LOOP]]:
>From 67801c511c2286f2773b5eb5e0ed9e9971f888b3 Mon Sep 17 00:00:00 2001
From: Luke Lau <luke at igalia.com>
Date: Wed, 26 Nov 2025 02:16:07 +0800
Subject: [PATCH 3/3] Use larger of the two bitwidths, matches how
SelectionDAGBuilder expands
---
llvm/lib/Transforms/Utils/SCCPSolver.cpp | 12 +++++++++---
.../Transforms/SCCP/get_vector_length-intrinsic.ll | 11 +++++++++++
2 files changed, 20 insertions(+), 3 deletions(-)
diff --git a/llvm/lib/Transforms/Utils/SCCPSolver.cpp b/llvm/lib/Transforms/Utils/SCCPSolver.cpp
index 7a5cc289fa5c9..951bf1ca62fc2 100644
--- a/llvm/lib/Transforms/Utils/SCCPSolver.cpp
+++ b/llvm/lib/Transforms/Utils/SCCPSolver.cpp
@@ -2099,15 +2099,20 @@ void SCCPInstVisitor::handleCallResult(CallBase &CB) {
ValueLatticeElement::getRange(Result));
}
if (II->getIntrinsicID() == Intrinsic::experimental_get_vector_length) {
- unsigned BitWidth = CB.getType()->getScalarSizeInBits();
Value *CountArg = II->getArgOperand(0);
Value *VF = II->getArgOperand(1);
bool Scalable = cast<ConstantInt>(II->getArgOperand(2))->isOne();
+
+ // Computation happens in the larger type.
+ unsigned BitWidth = std::max(CountArg->getType()->getScalarSizeInBits(),
+ VF->getType()->getScalarSizeInBits());
+
ConstantRange Count = getValueState(CountArg)
.asConstantRange(CountArg->getType(), false)
.zextOrTrunc(BitWidth);
- ConstantRange MaxLanes =
- getValueState(VF).asConstantRange(BitWidth, false);
+ ConstantRange MaxLanes = getValueState(VF)
+ .asConstantRange(VF->getType(), false)
+ .zextOrTrunc(BitWidth);
if (Scalable)
MaxLanes =
MaxLanes.multiply(getVScaleRange(II->getFunction(), BitWidth));
@@ -2121,6 +2126,7 @@ void SCCPInstVisitor::handleCallResult(CallBase &CB) {
if (Count.icmp(CmpInst::ICMP_ULE, MaxLanes))
Result = Count;
+ Result = Result.zextOrTrunc(II->getType()->getScalarSizeInBits());
return (void)mergeInValue(ValueState[II], II,
ValueLatticeElement::getRange(Result));
}
diff --git a/llvm/test/Transforms/SCCP/get_vector_length-intrinsic.ll b/llvm/test/Transforms/SCCP/get_vector_length-intrinsic.ll
index 3cb6154447631..d0741161e729e 100644
--- a/llvm/test/Transforms/SCCP/get_vector_length-intrinsic.ll
+++ b/llvm/test/Transforms/SCCP/get_vector_length-intrinsic.ll
@@ -134,3 +134,14 @@ loop:
exit:
ret i32 %x
}
+
+define i1 @result_le_overflow() {
+; CHECK-LABEL: define i1 @result_le_overflow() {
+; CHECK-NEXT: [[X:%.*]] = call i32 @llvm.experimental.get.vector.length.i64(i64 4294967296, i32 4, i1 false)
+; CHECK-NEXT: [[RES:%.*]] = icmp ule i32 [[X]], 3
+; CHECK-NEXT: ret i1 [[RES]]
+;
+ %x = call i32 @llvm.experimental.get.vector.length(i64 u0x100000000, i32 4, i1 false)
+ %res = icmp ule i32 %x, 3
+ ret i1 %res
+}
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