[llvm] acfd1da - [RISCV] Add further constraints on vsetvli intrinsics range (#219417)
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Sun Aug 30 21:07:56 PDT 2026
Author: Luke Lau
Date: 2026-08-31T04:07:51Z
New Revision: acfd1da182f4794a782d629698d8fd3a4fdc0f7d
URL: https://github.com/llvm/llvm-project/commit/acfd1da182f4794a782d629698d8fd3a4fdc0f7d
DIFF: https://github.com/llvm/llvm-project/commit/acfd1da182f4794a782d629698d8fd3a4fdc0f7d.diff
LOG: [RISCV] Add further constraints on vsetvli intrinsics range (#219417)
The spec also mandates:
- `ceil(AVL / 2) ≤ vl ≤ VLMAX if AVL < (2 * VLMAX)`
- `vl = VLMAX if AVL ≥ (2 * VLMAX)`
This also reworks the constraints to be based on ConstantRange so `vl =
AVL if AVL ≤ VLMAX` is no longer restricted to constants.
Added:
Modified:
llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp
llvm/test/Transforms/InstCombine/RISCV/riscv-vsetvli-range.ll
Removed:
################################################################################
diff --git a/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp b/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp
index f51e47895c4bb..cd14ff3d2dded 100644
--- a/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp
+++ b/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp
@@ -3786,21 +3786,36 @@ RISCVTTIImpl::instCombineIntrinsic(InstCombiner &IC, IntrinsicInst &II) const {
// only the VLMAX upper bound is sound.
ConstantRange VLRange = VLMAXRange;
if (HasAVL) {
- APInt MaxVL = VLMAXRange.getUnsignedMax();
+ // vl ≤ VLMAX
+ VLRange =
+ ConstantRange::makeAllowedICmpRegion(CmpInst::ICMP_ULE, VLMAXRange);
+
Value *AVL = II.getArgOperand(0);
+ ConstantRange AVLRange = computeConstantRangeIncludingKnownBits(
+ AVL, /*ForSigned=*/false,
+ IC.getSimplifyQuery().getWithInstruction(&II));
+
+ // vl = AVL if AVL ≤ VLMAX
+ if (AVLRange.icmp(CmpInst::ICMP_ULE, VLMAXRange))
+ return IC.replaceInstUsesWith(II, AVL);
+
+ // vl ≤ AVL
+ VLRange = VLRange.umin(AVLRange.getUnsignedMax());
+
// vl > 0 if AVL > 0
- APInt MinVL = APInt(BitWidth, isKnownNonZero(AVL, DL) ? 1 : 0);
- if (auto *AVLC = dyn_cast<ConstantInt>(AVL)) {
- const APInt &C = AVLC->getValue();
- // A constant AVL not exceeding the smallest possible VLMAX means vl is
- // exactly AVL, so replace the intrinsic with that constant.
- if (C.ule(VLMAXRange.getUnsignedMin()))
- return IC.replaceInstUsesWith(II, ConstantInt::get(II.getType(), C));
- VLRange =
- ConstantRange::getNonEmpty(MinVL, APIntOps::umin(C, MaxVL) + 1);
- } else {
- VLRange = ConstantRange::getNonEmpty(MinVL, MaxVL + 1);
- }
+ if (AVLRange.icmp(CmpInst::ICMP_UGT, APInt::getZero(BitWidth)))
+ VLRange = VLRange.umax(APInt(BitWidth, 1));
+
+ // vl = VLMAX if AVL ≥ (2 * VLMAX)
+ ConstantRange TwoVLMAX = VLMAXRange.multiply(APInt(BitWidth, 2));
+ if (AVLRange.icmp(CmpInst::ICMP_UGE, TwoVLMAX))
+ VLRange = VLRange.intersectWith(VLMAXRange);
+
+ // ceil(AVL / 2) ≤ vl ≤ VLMAX if AVL < (2 * VLMAX)
+ if (AVLRange.icmp(CmpInst::ICMP_ULT, TwoVLMAX))
+ VLRange = VLRange.umax(APIntOps::RoundingUDiv(AVLRange.getUnsignedMin(),
+ APInt(BitWidth, 2),
+ APInt::Rounding::UP));
}
ConstantRange OldRange =
diff --git a/llvm/test/Transforms/InstCombine/RISCV/riscv-vsetvli-range.ll b/llvm/test/Transforms/InstCombine/RISCV/riscv-vsetvli-range.ll
index 837ae6a9eb702..f74ec414077ab 100644
--- a/llvm/test/Transforms/InstCombine/RISCV/riscv-vsetvli-range.ll
+++ b/llvm/test/Transforms/InstCombine/RISCV/riscv-vsetvli-range.ll
@@ -34,11 +34,11 @@ define i64 @vsetvli_const_avl_at_min128() {
}
; AVL == 20 sits in (MinVLMAX, ...) at VLEN128, so vl is only known to be
-; [0, 20]; at VLEN512 it is still below VLMAX (64), so vl == 20 folds.
+; [10, 20]; at VLEN512 it is still below VLMAX (64), so vl == 20 folds.
define i64 @vsetvli_const_avl_mid() {
; VLEN128-LABEL: define i64 @vsetvli_const_avl_mid(
; VLEN128-SAME: ) #[[ATTR0]] {
-; VLEN128-NEXT: [[VL:%.*]] = call range(i64 1, 21) i64 @llvm.riscv.vsetvli.i64(i64 20, i64 0, i64 0)
+; VLEN128-NEXT: [[VL:%.*]] = call range(i64 10, 21) i64 @llvm.riscv.vsetvli.i64(i64 20, i64 0, i64 0)
; VLEN128-NEXT: ret i64 [[VL]]
;
; VLEN512-LABEL: define i64 @vsetvli_const_avl_mid(
@@ -50,12 +50,17 @@ define i64 @vsetvli_const_avl_mid() {
}
; AVL far above the largest VLMAX (8192): vl is capped by VLMAX, giving the
-; VLEN-independent range [0, 8192].
+; VLEN-independent range [MinVLMAX, 8192].
define i64 @vsetvli_const_avl_above_max() {
-; CHECK-LABEL: define i64 @vsetvli_const_avl_above_max(
-; CHECK-SAME: ) #[[ATTR0]] {
-; CHECK-NEXT: [[VL:%.*]] = call range(i64 1, 8193) i64 @llvm.riscv.vsetvli.i64(i64 100000, i64 0, i64 0)
-; CHECK-NEXT: ret i64 [[VL]]
+; VLEN128-LABEL: define i64 @vsetvli_const_avl_above_max(
+; VLEN128-SAME: ) #[[ATTR0]] {
+; VLEN128-NEXT: [[VL:%.*]] = call range(i64 16, 8193) i64 @llvm.riscv.vsetvli.i64(i64 100000, i64 0, i64 0)
+; VLEN128-NEXT: ret i64 [[VL]]
+;
+; VLEN512-LABEL: define i64 @vsetvli_const_avl_above_max(
+; VLEN512-SAME: ) #[[ATTR0]] {
+; VLEN512-NEXT: [[VL:%.*]] = call range(i64 64, 8193) i64 @llvm.riscv.vsetvli.i64(i64 100000, i64 0, i64 0)
+; VLEN512-NEXT: ret i64 [[VL]]
;
%vl = call i64 @llvm.riscv.vsetvli.i64(i64 100000, i64 0, i64 0)
ret i64 %vl
@@ -124,7 +129,7 @@ define i1 @vsetvli_runtime_avl_gt_max_folds(i64 %avl) {
ret i1 %c
}
-; vl known > 0, so range must be > 0
+; avl known > 0, so range must be > 0
define i64 @vsetvli_vl_known_nonzero(i64 %x) {
; CHECK-LABEL: define i64 @vsetvli_vl_known_nonzero(
; CHECK-SAME: i64 [[X:%.*]]) #[[ATTR0]] {
@@ -136,3 +141,15 @@ define i64 @vsetvli_vl_known_nonzero(i64 %x) {
%vl = call i64 @llvm.riscv.vsetvli.i64(i64 %avl, i64 0, i64 0)
ret i64 %vl
}
+
+; avl known <= vlmax, so vl = avl
+define i64 @vsetvli_avl_known_lt_vlmax(i64 %x) {
+; CHECK-LABEL: define i64 @vsetvli_avl_known_lt_vlmax(
+; CHECK-SAME: i64 [[X:%.*]]) #[[ATTR0]] {
+; CHECK-NEXT: [[VL:%.*]] = and i64 [[X]], 7
+; CHECK-NEXT: ret i64 [[VL]]
+;
+ %avl = and i64 %x, 7
+ %vl = call i64 @llvm.riscv.vsetvli.i64(i64 %avl, i64 0, i64 0)
+ ret i64 %vl
+}
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