https://github.com/arsenm updated 
https://github.com/llvm/llvm-project/pull/174101

>From 4c4344feefa0084aecfc61b22fa27c5b673e0849 Mon Sep 17 00:00:00 2001
From: Matt Arsenault <[email protected]>
Date: Wed, 31 Dec 2025 12:13:26 +0100
Subject: [PATCH] InstCombine: Rudimentary support of shufflevector in
 SimplifyDemandedFPClass

This should look more like the computeKnownFPClass handling, with knowledge
of demanded vector elements.
---
 .../InstCombineSimplifyDemanded.cpp           |  11 +
 ...simplify-demanded-fpclass-shufflevector.ll | 269 ++++++++++++++++++
 2 files changed, 280 insertions(+)
 create mode 100644 
llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-shufflevector.ll

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp 
b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
index 9ae6ab25c6033..b71133a7b6470 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
@@ -2313,6 +2313,17 @@ Value 
*InstCombinerImpl::SimplifyDemandedUseFPClass(Value *V,
     Known = KnownVec | KnownInserted;
     break;
   }
+  case Instruction::ShuffleVector: {
+    KnownFPClass KnownLHS, KnownRHS;
+    if (SimplifyDemandedFPClass(I, 1, DemandedMask, KnownRHS, Depth + 1) ||
+        SimplifyDemandedFPClass(I, 0, DemandedMask, KnownLHS, Depth + 1))
+      return I;
+
+    // TODO: This is overly conservative and should consider demanded elements,
+    // and splats.
+    Known = KnownLHS | KnownRHS;
+    break;
+  }
   default:
     Known = computeKnownFPClass(I, DemandedMask, CxtI, Depth + 1);
     break;
diff --git 
a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-shufflevector.ll 
b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-shufflevector.ll
new file mode 100644
index 0000000000000..042e77c3ee2a9
--- /dev/null
+++ 
b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass-shufflevector.ll
@@ -0,0 +1,269 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py 
UTC_ARGS: --version 6
+; RUN: opt -S -passes=instcombine < %s | FileCheck %s
+
+declare nofpclass(inf zero sub norm) <4 x half> @returns_nan()
+declare nofpclass(nan zero sub norm) <4 x half> @returns_inf()
+declare nofpclass(inf zero sub norm) half @returns_nan_f16()
+
+define nofpclass(inf zero sub norm) <4 x half> 
@ret_only_nan__shufflevector_unknown(<4 x half> %vec0, <4 x half> %vec1) {
+; CHECK-LABEL: define nofpclass(inf zero sub norm) <4 x half> 
@ret_only_nan__shufflevector_unknown(
+; CHECK-SAME: <4 x half> [[VEC0:%.*]], <4 x half> [[VEC1:%.*]]) {
+; CHECK-NEXT:    [[SHUFFLE:%.*]] = shufflevector <4 x half> [[VEC0]], <4 x 
half> [[VEC1]], <4 x i32> <i32 6, i32 2, i32 3, i32 0>
+; CHECK-NEXT:    ret <4 x half> [[SHUFFLE]]
+;
+  %shuffle = shufflevector <4 x half> %vec0, <4 x half> %vec1, <4 x i32> <i32 
6, i32 2, i32 3, i32 0>
+  ret <4 x half> %shuffle
+}
+
+define nofpclass(qnan inf zero sub norm) <4 x half> 
@ret_only_snan__shufflevector_unknown(<4 x half> %vec0, <4 x half> %vec1) {
+; CHECK-LABEL: define nofpclass(qnan inf zero sub norm) <4 x half> 
@ret_only_snan__shufflevector_unknown(
+; CHECK-SAME: <4 x half> [[VEC0:%.*]], <4 x half> [[VEC1:%.*]]) {
+; CHECK-NEXT:    [[SHUFFLE:%.*]] = shufflevector <4 x half> [[VEC0]], <4 x 
half> [[VEC1]], <4 x i32> <i32 6, i32 2, i32 3, i32 0>
+; CHECK-NEXT:    ret <4 x half> [[SHUFFLE]]
+;
+  %shuffle = shufflevector <4 x half> %vec0, <4 x half> %vec1, <4 x i32> <i32 
6, i32 2, i32 3, i32 0>
+  ret <4 x half> %shuffle
+}
+
+define nofpclass(snan inf zero sub norm) <4 x half> 
@ret_only_qnan__shufflevector_unknown(<4 x half> %vec0, <4 x half> %vec1) {
+; CHECK-LABEL: define nofpclass(snan inf zero sub norm) <4 x half> 
@ret_only_qnan__shufflevector_unknown(
+; CHECK-SAME: <4 x half> [[VEC0:%.*]], <4 x half> [[VEC1:%.*]]) {
+; CHECK-NEXT:    [[SHUFFLE:%.*]] = shufflevector <4 x half> [[VEC0]], <4 x 
half> [[VEC1]], <4 x i32> <i32 6, i32 2, i32 3, i32 0>
+; CHECK-NEXT:    ret <4 x half> [[SHUFFLE]]
+;
+  %shuffle = shufflevector <4 x half> %vec0, <4 x half> %vec1, <4 x i32> <i32 
6, i32 2, i32 3, i32 0>
+  ret <4 x half> %shuffle
+}
+
+define nofpclass(nan inf sub norm) <4 x half> 
@ret_only_zero__shufflevector_unknown(<4 x half> %vec0, <4 x half> %vec1) {
+; CHECK-LABEL: define nofpclass(nan inf sub norm) <4 x half> 
@ret_only_zero__shufflevector_unknown(
+; CHECK-SAME: <4 x half> [[VEC0:%.*]], <4 x half> [[VEC1:%.*]]) {
+; CHECK-NEXT:    [[SHUFFLE:%.*]] = shufflevector <4 x half> [[VEC0]], <4 x 
half> [[VEC1]], <4 x i32> <i32 6, i32 2, i32 3, i32 0>
+; CHECK-NEXT:    ret <4 x half> [[SHUFFLE]]
+;
+  %shuffle = shufflevector <4 x half> %vec0, <4 x half> %vec1, <4 x i32> <i32 
6, i32 2, i32 3, i32 0>
+  ret <4 x half> %shuffle
+}
+
+define nofpclass(nan inf nzero sub norm) <4 x half> 
@ret_only_pzero__shufflevector_unknown(<4 x half> %vec0, <4 x half> %vec1) {
+; CHECK-LABEL: define nofpclass(nan inf nzero sub norm) <4 x half> 
@ret_only_pzero__shufflevector_unknown(
+; CHECK-SAME: <4 x half> [[VEC0:%.*]], <4 x half> [[VEC1:%.*]]) {
+; CHECK-NEXT:    ret <4 x half> zeroinitializer
+;
+  %shuffle = shufflevector <4 x half> %vec0, <4 x half> %vec1, <4 x i32> <i32 
6, i32 2, i32 3, i32 0>
+  ret <4 x half> %shuffle
+}
+
+define nofpclass(nan inf pzero sub norm) <4 x half> 
@ret_only_nzero__shufflevector_unknown(<4 x half> %vec0, <4 x half> %vec1) {
+; CHECK-LABEL: define nofpclass(nan inf pzero sub norm) <4 x half> 
@ret_only_nzero__shufflevector_unknown(
+; CHECK-SAME: <4 x half> [[VEC0:%.*]], <4 x half> [[VEC1:%.*]]) {
+; CHECK-NEXT:    ret <4 x half> splat (half 0xH8000)
+;
+  %shuffle = shufflevector <4 x half> %vec0, <4 x half> %vec1, <4 x i32> <i32 
6, i32 2, i32 3, i32 0>
+  ret <4 x half> %shuffle
+}
+
+define nofpclass(nan zero sub norm) <4 x half> 
@ret_only_inf__shufflevector_unknown(<4 x half> %vec0, <4 x half> %vec1) {
+; CHECK-LABEL: define nofpclass(nan zero sub norm) <4 x half> 
@ret_only_inf__shufflevector_unknown(
+; CHECK-SAME: <4 x half> [[VEC0:%.*]], <4 x half> [[VEC1:%.*]]) {
+; CHECK-NEXT:    [[SHUFFLE:%.*]] = shufflevector <4 x half> [[VEC0]], <4 x 
half> [[VEC1]], <4 x i32> <i32 6, i32 2, i32 3, i32 0>
+; CHECK-NEXT:    ret <4 x half> [[SHUFFLE]]
+;
+  %shuffle = shufflevector <4 x half> %vec0, <4 x half> %vec1, <4 x i32> <i32 
6, i32 2, i32 3, i32 0>
+  ret <4 x half> %shuffle
+}
+
+define nofpclass(nan ninf zero sub norm) <4 x half> 
@ret_only_pinf__shufflevector_unknown(<4 x half> %vec0, <4 x half> %vec1) {
+; CHECK-LABEL: define nofpclass(nan ninf zero sub norm) <4 x half> 
@ret_only_pinf__shufflevector_unknown(
+; CHECK-SAME: <4 x half> [[VEC0:%.*]], <4 x half> [[VEC1:%.*]]) {
+; CHECK-NEXT:    ret <4 x half> splat (half 0xH7C00)
+;
+  %shuffle = shufflevector <4 x half> %vec0, <4 x half> %vec1, <4 x i32> <i32 
6, i32 2, i32 3, i32 0>
+  ret <4 x half> %shuffle
+}
+
+define nofpclass(nan pinf zero sub norm) <4 x half> 
@ret_only_ninf__shufflevector_unknown(<4 x half> %vec0, <4 x half> %vec1) {
+; CHECK-LABEL: define nofpclass(nan pinf zero sub norm) <4 x half> 
@ret_only_ninf__shufflevector_unknown(
+; CHECK-SAME: <4 x half> [[VEC0:%.*]], <4 x half> [[VEC1:%.*]]) {
+; CHECK-NEXT:    ret <4 x half> splat (half 0xHFC00)
+;
+  %shuffle = shufflevector <4 x half> %vec0, <4 x half> %vec1, <4 x i32> <i32 
6, i32 2, i32 3, i32 0>
+  ret <4 x half> %shuffle
+}
+
+define nofpclass(nan) <4 x half> 
@ret_no_nan__shufflevector_one_input_select_nan(i1 %cond, <4 x half> %unknown) {
+; CHECK-LABEL: define nofpclass(nan) <4 x half> 
@ret_no_nan__shufflevector_one_input_select_nan(
+; CHECK-SAME: i1 [[COND:%.*]], <4 x half> [[UNKNOWN:%.*]]) {
+; CHECK-NEXT:    [[NAN:%.*]] = call <4 x half> @returns_nan()
+; CHECK-NEXT:    [[SHUFFLE:%.*]] = shufflevector <4 x half> [[UNKNOWN]], <4 x 
half> poison, <4 x i32> <i32 3, i32 1, i32 0, i32 0>
+; CHECK-NEXT:    ret <4 x half> [[SHUFFLE]]
+;
+  %nan = call <4 x half> @returns_nan()
+  %select = select i1 %cond, <4 x half> %nan, <4 x half> %unknown
+  %shuffle = shufflevector <4 x half> %select, <4 x half> poison, <4 x i32> 
<i32 3, i32 1, i32 0, i32 0>
+  ret <4 x half> %shuffle
+}
+
+define nofpclass(nan) <4 x half> 
@ret_no_nan__shufflevector_two_input_select_nans(i1 %cond, <4 x half> 
%unknown0, <4 x half> %unknown1) {
+; CHECK-LABEL: define nofpclass(nan) <4 x half> 
@ret_no_nan__shufflevector_two_input_select_nans(
+; CHECK-SAME: i1 [[COND:%.*]], <4 x half> [[UNKNOWN0:%.*]], <4 x half> 
[[UNKNOWN1:%.*]]) {
+; CHECK-NEXT:    [[NAN:%.*]] = call <4 x half> @returns_nan()
+; CHECK-NEXT:    [[SHUFFLE:%.*]] = shufflevector <4 x half> [[UNKNOWN0]], <4 x 
half> [[UNKNOWN1]], <4 x i32> <i32 4, i32 7, i32 1, i32 3>
+; CHECK-NEXT:    ret <4 x half> [[SHUFFLE]]
+;
+  %nan = call <4 x half> @returns_nan()
+  %select0 = select i1 %cond, <4 x half> %nan, <4 x half> %unknown0
+  %select1 = select i1 %cond, <4 x half> %unknown1, <4 x half> %nan
+  %shuffle = shufflevector <4 x half> %select0, <4 x half> %select1, <4 x i32> 
<i32 4, i32 7, i32 1, i32 3>
+  ret <4 x half> %shuffle
+}
+
+define nofpclass(nan) <4 x half> 
@ret_no_nan__shufflevector_two_input_eliminate_vector0(<4 x half> %unknown) {
+; CHECK-LABEL: define nofpclass(nan) <4 x half> 
@ret_no_nan__shufflevector_two_input_eliminate_vector0(
+; CHECK-SAME: <4 x half> [[UNKNOWN:%.*]]) {
+; CHECK-NEXT:    [[NAN:%.*]] = call <4 x half> @returns_nan()
+; CHECK-NEXT:    [[SHUFFLE:%.*]] = shufflevector <4 x half> [[UNKNOWN]], <4 x 
half> poison, <4 x i32> <i32 0, i32 3, i32 poison, i32 poison>
+; CHECK-NEXT:    ret <4 x half> [[SHUFFLE]]
+;
+  %nan = call <4 x half> @returns_nan()
+  %shuffle = shufflevector <4 x half> %nan, <4 x half> %unknown, <4 x i32> 
<i32 4, i32 7, i32 1, i32 3>
+  ret <4 x half> %shuffle
+}
+
+define nofpclass(nan) <4 x half> 
@ret_no_nan__shufflevector_two_input_eliminate_vector1(<4 x half> %unknown) {
+; CHECK-LABEL: define nofpclass(nan) <4 x half> 
@ret_no_nan__shufflevector_two_input_eliminate_vector1(
+; CHECK-SAME: <4 x half> [[UNKNOWN:%.*]]) {
+; CHECK-NEXT:    [[NAN:%.*]] = call <4 x half> @returns_nan()
+; CHECK-NEXT:    [[SHUFFLE:%.*]] = shufflevector <4 x half> [[UNKNOWN]], <4 x 
half> poison, <4 x i32> <i32 poison, i32 poison, i32 1, i32 3>
+; CHECK-NEXT:    ret <4 x half> [[SHUFFLE]]
+;
+  %nan = call <4 x half> @returns_nan()
+  %shuffle = shufflevector <4 x half> %unknown, <4 x half> %nan, <4 x i32> 
<i32 4, i32 7, i32 1, i32 3>
+  ret <4 x half> %shuffle
+}
+
+; Cannot simplify
+define nofpclass(inf nan) <4 x half> 
@ret_nonan_noinf___shuffle_not_nan_not_inf(i1 %cond, <4 x half> nofpclass(nan) 
%not.nan, <4 x half> %not.inf) {
+; CHECK-LABEL: define nofpclass(nan inf) <4 x half> 
@ret_nonan_noinf___shuffle_not_nan_not_inf(
+; CHECK-SAME: i1 [[COND:%.*]], <4 x half> nofpclass(nan) [[NOT_NAN:%.*]], <4 x 
half> [[NOT_INF:%.*]]) {
+; CHECK-NEXT:    [[SHUFFLE:%.*]] = shufflevector <4 x half> [[NOT_NAN]], <4 x 
half> [[NOT_INF]], <4 x i32> <i32 4, i32 2, i32 3, i32 0>
+; CHECK-NEXT:    ret <4 x half> [[SHUFFLE]]
+;
+  %shuffle = shufflevector <4 x half> %not.nan, <4 x half> %not.inf, <4 x i32> 
<i32 4, i32 2, i32 3, i32 0>
+  ret <4 x half> %shuffle
+}
+
+; poison
+define nofpclass(inf nan) <4 x half> 
@ret_nonan_noinf__shufflevector_nan_inf(i1 %cond) {
+; CHECK-LABEL: define nofpclass(nan inf) <4 x half> 
@ret_nonan_noinf__shufflevector_nan_inf(
+; CHECK-SAME: i1 [[COND:%.*]]) {
+; CHECK-NEXT:    [[NAN:%.*]] = call <4 x half> @returns_nan()
+; CHECK-NEXT:    [[INF:%.*]] = call <4 x half> @returns_inf()
+; CHECK-NEXT:    ret <4 x half> <half undef, half poison, half poison, half 
poison>
+;
+  %nan = call <4 x half> @returns_nan()
+  %inf = call <4 x half> @returns_inf()
+  %shuffle = shufflevector <4 x half> %inf, <4 x half> %nan, <4 x i32> <i32 4, 
i32 2, i32 3, i32 0>
+  ret <4 x half> %shuffle
+}
+
+define nofpclass(ninf nnorm nsub nzero) <4 x half> 
@ret_positives___shuffle_fabs_positive_or_nans(i1 %cond, <4 x half> 
nofpclass(ninf nnorm nsub nzero) %known.positive0, <4 x half> nofpclass(ninf 
nnorm nsub nzero) %known.positive1) {
+; CHECK-LABEL: define nofpclass(ninf nzero nsub nnorm) <4 x half> 
@ret_positives___shuffle_fabs_positive_or_nans(
+; CHECK-SAME: i1 [[COND:%.*]], <4 x half> nofpclass(ninf nzero nsub nnorm) 
[[KNOWN_POSITIVE0:%.*]], <4 x half> nofpclass(ninf nzero nsub nnorm) 
[[KNOWN_POSITIVE1:%.*]]) {
+; CHECK-NEXT:    [[TMP1:%.*]] = shufflevector <4 x half> [[KNOWN_POSITIVE0]], 
<4 x half> [[KNOWN_POSITIVE1]], <4 x i32> <i32 4, i32 2, i32 3, i32 0>
+; CHECK-NEXT:    [[SHUFFLE:%.*]] = call <4 x half> @llvm.fabs.v4f16(<4 x half> 
[[TMP1]])
+; CHECK-NEXT:    ret <4 x half> [[SHUFFLE]]
+;
+  %fabs.0 = call <4 x half> @llvm.fabs.v4f16(<4 x half> %known.positive0)
+  %fabs.1 = call <4 x half> @llvm.fabs.v4f16(<4 x half> %known.positive1)
+  %shuffle = shufflevector <4 x half> %fabs.0, <4 x half> %fabs.1, <4 x i32> 
<i32 4, i32 2, i32 3, i32 0>
+  ret <4 x half> %shuffle
+}
+
+define nofpclass(ninf nnorm nsub nzero) <4 x half> 
@ret_positives___shuffle_fabs_positives(i1 %cond, <4 x half> nofpclass(nan ninf 
nnorm nsub nzero) %known.positive0, <4 x half> nofpclass(nan ninf nnorm nsub 
nzero) %known.positive1) {
+; CHECK-LABEL: define nofpclass(ninf nzero nsub nnorm) <4 x half> 
@ret_positives___shuffle_fabs_positives(
+; CHECK-SAME: i1 [[COND:%.*]], <4 x half> nofpclass(nan ninf nzero nsub nnorm) 
[[KNOWN_POSITIVE0:%.*]], <4 x half> nofpclass(nan ninf nzero nsub nnorm) 
[[KNOWN_POSITIVE1:%.*]]) {
+; CHECK-NEXT:    [[SHUFFLE:%.*]] = shufflevector <4 x half> 
[[KNOWN_POSITIVE0]], <4 x half> [[KNOWN_POSITIVE1]], <4 x i32> <i32 4, i32 2, 
i32 3, i32 0>
+; CHECK-NEXT:    ret <4 x half> [[SHUFFLE]]
+;
+  %fabs.0 = call <4 x half> @llvm.fabs.v4f16(<4 x half> %known.positive0)
+  %fabs.1 = call <4 x half> @llvm.fabs.v4f16(<4 x half> %known.positive1)
+  %shuffle = shufflevector <4 x half> %fabs.0, <4 x half> %fabs.1, <4 x i32> 
<i32 4, i32 2, i32 3, i32 0>
+  ret <4 x half> %shuffle
+}
+
+; TODO: Should be able to eliminate fabs with no-nans from return
+define nofpclass(nan ninf nnorm nsub nzero) <4 x half> 
@ret_positives_non_nan___shuffle_fabs(i1 %cond, <4 x half> nofpclass(ninf nnorm 
nsub nzero) %known.positive0, <4 x half> nofpclass(ninf nnorm nsub nzero) 
%known.positive1) {
+; CHECK-LABEL: define nofpclass(nan ninf nzero nsub nnorm) <4 x half> 
@ret_positives_non_nan___shuffle_fabs(
+; CHECK-SAME: i1 [[COND:%.*]], <4 x half> nofpclass(ninf nzero nsub nnorm) 
[[KNOWN_POSITIVE0:%.*]], <4 x half> nofpclass(ninf nzero nsub nnorm) 
[[KNOWN_POSITIVE1:%.*]]) {
+; CHECK-NEXT:    [[TMP1:%.*]] = shufflevector <4 x half> [[KNOWN_POSITIVE0]], 
<4 x half> [[KNOWN_POSITIVE1]], <4 x i32> <i32 4, i32 2, i32 3, i32 0>
+; CHECK-NEXT:    [[SHUFFLE:%.*]] = call <4 x half> @llvm.fabs.v4f16(<4 x half> 
[[TMP1]])
+; CHECK-NEXT:    ret <4 x half> [[SHUFFLE]]
+;
+  %fabs.0 = call <4 x half> @llvm.fabs.v4f16(<4 x half> %known.positive0)
+  %fabs.1 = call <4 x half> @llvm.fabs.v4f16(<4 x half> %known.positive1)
+  %shuffle = shufflevector <4 x half> %fabs.0, <4 x half> %fabs.1, <4 x i32> 
<i32 4, i32 2, i32 3, i32 0>
+  ret <4 x half> %shuffle
+}
+
+define nofpclass(nan) <4 x half> @ret_nonan_splat(i1 %cond, half %unknown) {
+; CHECK-LABEL: define nofpclass(nan) <4 x half> @ret_nonan_splat(
+; CHECK-SAME: i1 [[COND:%.*]], half [[UNKNOWN:%.*]]) {
+; CHECK-NEXT:    [[NAN:%.*]] = call half @returns_nan_f16()
+; CHECK-NEXT:    [[UNKNOWN_VEC:%.*]] = insertelement <4 x half> poison, half 
[[UNKNOWN]], i64 0
+; CHECK-NEXT:    [[SPLAT_UNKNOWN:%.*]] = shufflevector <4 x half> 
[[UNKNOWN_VEC]], <4 x half> poison, <4 x i32> zeroinitializer
+; CHECK-NEXT:    ret <4 x half> [[SPLAT_UNKNOWN]]
+;
+  %nan = call half @returns_nan_f16()
+  %nan.vec = insertelement <4 x half> poison, half %nan, i32 0
+  %unknown.vec = insertelement <4 x half> poison, half %unknown, i32 0
+  %splat.nan = shufflevector <4 x half> %nan.vec, <4 x half> poison, <4 x i32> 
zeroinitializer
+  %splat.unknown = shufflevector <4 x half> %unknown.vec, <4 x half> poison, 
<4 x i32> zeroinitializer
+  %select = select i1 %cond, <4 x half> %splat.nan, <4 x half> %splat.unknown
+  ret <4 x half> %select
+}
+
+define nofpclass(nan) <4 x half> @ret_nonan_splat_select_unknown_or_nan(i1 
%cond, half %unknown) {
+; CHECK-LABEL: define nofpclass(nan) <4 x half> 
@ret_nonan_splat_select_unknown_or_nan(
+; CHECK-SAME: i1 [[COND:%.*]], half [[UNKNOWN:%.*]]) {
+; CHECK-NEXT:    [[NAN:%.*]] = call half @returns_nan_f16()
+; CHECK-NEXT:    [[SELECT_VEC:%.*]] = insertelement <4 x half> poison, half 
[[UNKNOWN]], i64 0
+; CHECK-NEXT:    [[SPLAT:%.*]] = shufflevector <4 x half> [[SELECT_VEC]], <4 x 
half> poison, <4 x i32> zeroinitializer
+; CHECK-NEXT:    ret <4 x half> [[SPLAT]]
+;
+  %nan = call half @returns_nan_f16()
+  %select = select i1 %cond, half %nan, half %unknown
+  %select.vec = insertelement <4 x half> poison, half %select, i32 0
+  %splat = shufflevector <4 x half> %select.vec, <4 x half> poison, <4 x i32> 
zeroinitializer
+  ret <4 x half> %splat
+}
+
+; Do not rewrite exp into fadd
+define nofpclass(snan) <4 x half> @ret_nonnan_rhs_taints_known_nan_result(i1 
%cond, <4 x half> %unknown) {
+; CHECK-LABEL: define nofpclass(snan) <4 x half> 
@ret_nonnan_rhs_taints_known_nan_result(
+; CHECK-SAME: i1 [[COND:%.*]], <4 x half> [[UNKNOWN:%.*]]) {
+; CHECK-NEXT:    [[NAN:%.*]] = call <4 x half> @returns_nan()
+; CHECK-NEXT:    [[SHUFFLE:%.*]] = shufflevector <4 x half> [[NAN]], <4 x 
half> [[UNKNOWN]], <4 x i32> <i32 5, i32 0, i32 1, i32 3>
+; CHECK-NEXT:    [[EXP:%.*]] = call <4 x half> @llvm.exp.v4f16(<4 x half> 
[[SHUFFLE]])
+; CHECK-NEXT:    ret <4 x half> [[EXP]]
+;
+  %nan = call <4 x half> @returns_nan()
+  %shuffle = shufflevector <4 x half> %nan, <4 x half> %unknown, <4 x i32> 
<i32 5, i32 0, i32 1, i32 3>
+  %exp = call <4 x half> @llvm.exp.v4f16(<4 x half> %shuffle)
+  ret <4 x half> %exp
+}
+
+; Do not rewrite exp into fadd
+define nofpclass(snan) <4 x half> @ret_nonnan_lhs_taints_known_nan_result(i1 
%cond, <4 x half> %unknown) {
+; CHECK-LABEL: define nofpclass(snan) <4 x half> 
@ret_nonnan_lhs_taints_known_nan_result(
+; CHECK-SAME: i1 [[COND:%.*]], <4 x half> [[UNKNOWN:%.*]]) {
+; CHECK-NEXT:    [[NAN:%.*]] = call <4 x half> @returns_nan()
+; CHECK-NEXT:    [[SHUFFLE:%.*]] = shufflevector <4 x half> [[UNKNOWN]], <4 x 
half> [[NAN]], <4 x i32> <i32 5, i32 0, i32 1, i32 3>
+; CHECK-NEXT:    [[EXP:%.*]] = call <4 x half> @llvm.exp.v4f16(<4 x half> 
[[SHUFFLE]])
+; CHECK-NEXT:    ret <4 x half> [[EXP]]
+;
+  %nan = call <4 x half> @returns_nan()
+  %shuffle = shufflevector <4 x half> %unknown, <4 x half> %nan, <4 x i32> 
<i32 5, i32 0, i32 1, i32 3>
+  %exp = call <4 x half> @llvm.exp.v4f16(<4 x half> %shuffle)
+  ret <4 x half> %exp
+}

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