From 699a9dd7c3d217f16c7dd0e6ea53738f7754ba6a Mon Sep 17 00:00:00 2001
From: Ahmed Bougacha <ahmed.bougacha@gmail.com>
Date: Tue, 1 Sep 2015 21:56:00 +0000
Subject: [PATCH] [ARM] Don't abort on variable-idx extractelt in
 ReconstructShuffle.

The code introduced in r244314 assumed that EXTRACT_VECTOR_ELT only
takes constant indices, but it does accept variables.
Bail out for those: we can't use them, as the shuffles we want to
reconstruct do require constant masks.

llvm-svn: 246594
---
 llvm/lib/Target/ARM/ARMISelLowering.cpp |  4 ++++
 llvm/test/CodeGen/ARM/vdup.ll           | 16 ++++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/llvm/lib/Target/ARM/ARMISelLowering.cpp b/llvm/lib/Target/ARM/ARMISelLowering.cpp
index 17c48287f059..f2915a4ab152 100644
--- a/llvm/lib/Target/ARM/ARMISelLowering.cpp
+++ b/llvm/lib/Target/ARM/ARMISelLowering.cpp
@@ -5554,6 +5554,10 @@ SDValue ARMTargetLowering::ReconstructShuffle(SDValue Op,
       // A shuffle can only come from building a vector from various
       // elements of other vectors.
       return SDValue();
+    } else if (!isa<ConstantSDNode>(V.getOperand(1))) {
+      // Furthermore, shuffles require a constant mask, whereas extractelts
+      // accept variable indices.
+      return SDValue();
     }
 
     // Add this element source to the list if it's not already there.
diff --git a/llvm/test/CodeGen/ARM/vdup.ll b/llvm/test/CodeGen/ARM/vdup.ll
index 36eebbfc4650..25c4807d9862 100644
--- a/llvm/test/CodeGen/ARM/vdup.ll
+++ b/llvm/test/CodeGen/ARM/vdup.ll
@@ -364,3 +364,19 @@ define <4 x float> @check_spr_splat4_lane1(<4 x float> %p, i16 %q) {
   %sub = fsub <4 x float> %splat.splat, %p
   ret <4 x float> %sub
 }
+
+; Also make sure we don't barf on variable-index extractelts, where we almost
+; could have generated a vdup.
+
+define <8 x i8> @check_i8_varidx(<16 x i8> %v, i32 %idx) {
+; CHECK-LABEL: check_i8_varidx:
+; CHECK: mov r[[FP:[0-9]+]], sp
+; CHECK: ldr r[[IDX:[0-9]+]], [r[[FP]], #4]
+; CHECK: mov r[[SPCOPY:[0-9]+]], sp
+; CHECK: vst1.64 {d{{.*}}, d{{.*}}}, [r[[SPCOPY]]:128], r[[IDX]]
+; CHECK: vld1.8 {d{{.*}}[]}, [r[[SPCOPY]]]
+  %x = extractelement <16 x i8> %v, i32 %idx
+  %1 = insertelement  <8 x i8> undef, i8 %x, i32 0
+  %2 = insertelement  <8 x i8> %1, i8 %x, i32 1
+  ret <8 x i8> %2
+}