[InstCombine] Canonicalize active lane mask params (#158065)

MDevereau · web-flow · commit ead4f3e271fd · 2025-09-12T16:35:58.000+01:00
Rewrite active lane mask intrinsics to begin their range from 0 when
both parameters are constant integers.
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -3952,6 +3952,19 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
     }
     break;
   }
+  case Intrinsic::get_active_lane_mask: {
+    const APInt *Op0, *Op1;
+    if (match(II->getOperand(0), m_StrictlyPositive(Op0)) &&
+        match(II->getOperand(1), m_APInt(Op1))) {
+      Type *OpTy = II->getOperand(0)->getType();
+      return replaceInstUsesWith(
+          *II, Builder.CreateIntrinsic(
+                   II->getType(), Intrinsic::get_active_lane_mask,
+                   {Constant::getNullValue(OpTy),
+                    ConstantInt::get(OpTy, Op1->usub_sat(*Op0))}));
+    }
+    break;
+  }
   default: {
     // Handle target specific intrinsics
     std::optional<Instruction *> V = targetInstCombineIntrinsic(*II);
diff --git a/llvm/test/Transforms/InstCombine/get_active_lane_mask.ll b/llvm/test/Transforms/InstCombine/get_active_lane_mask.ll
@@ -0,0 +1,38 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt < %s -passes=instcombine -S | FileCheck %s
+
+define <vscale x 4 x i1> @rewrite_range_nxv4i1() {
+; CHECK-LABEL: define <vscale x 4 x i1> @rewrite_range_nxv4i1() {
+; CHECK-NEXT:    [[MASK:%.*]] = call <vscale x 4 x i1> @llvm.get.active.lane.mask.nxv4i1.i32(i32 0, i32 3)
+; CHECK-NEXT:    ret <vscale x 4 x i1> [[MASK]]
+;
+  %mask = call <vscale x 4 x i1> @llvm.get.active.lane.mask.nxv4i1.i32(i32 1, i32 4)
+  ret <vscale x 4 x i1> %mask
+}
+
+define <vscale x 16 x i1> @rewrite_range_nxv16i1() {
+; CHECK-LABEL: define <vscale x 16 x i1> @rewrite_range_nxv16i1() {
+; CHECK-NEXT:    [[MASK:%.*]] = call <vscale x 16 x i1> @llvm.get.active.lane.mask.nxv16i1.i64(i64 0, i64 7)
+; CHECK-NEXT:    ret <vscale x 16 x i1> [[MASK]]
+;
+  %mask = call <vscale x 16 x i1> @llvm.get.active.lane.mask.nxv16i1.i64(i64 123123, i64 123130)
+  ret <vscale x 16 x i1> %mask
+}
+
+define <vscale x 16 x i1> @rewrite_range_nxv16i1_i128() {
+; CHECK-LABEL: define <vscale x 16 x i1> @rewrite_range_nxv16i1_i128() {
+; CHECK-NEXT:    [[MASK:%.*]] = call <vscale x 16 x i1> @llvm.get.active.lane.mask.nxv16i1.i128(i128 0, i128 10)
+; CHECK-NEXT:    ret <vscale x 16 x i1> [[MASK]]
+;
+  %mask = call <vscale x 16 x i1> @llvm.get.active.lane.mask.nxv16i1.i128(i128 18446744073709551616, i128 18446744073709551626)
+  ret <vscale x 16 x i1> %mask
+}
+
+define <vscale x 4 x i1> @bail_lhs_is_zero() {
+; CHECK-LABEL: define <vscale x 4 x i1> @bail_lhs_is_zero() {
+; CHECK-NEXT:    [[MASK:%.*]] = call <vscale x 4 x i1> @llvm.get.active.lane.mask.nxv4i1.i32(i32 0, i32 4)
+; CHECK-NEXT:    ret <vscale x 4 x i1> [[MASK]]
+;
+  %mask = call <vscale x 4 x i1> @llvm.get.active.lane.mask.nxv4i1.i32(i32 0, i32 4)
+  ret <vscale x 4 x i1> %mask
+}
