[llvm] r246594 - [ARM] Don't abort on variable-idx extractelt in ReconstructShuffle.

[Ahmed Bougacha via llvm-commits]

Author: ab
Date: Tue Sep  1 16:56:00 2015
New Revision: 246594

URL: http://llvm.org/viewvc/llvm-project?rev=246594&view=rev
Log:
[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.

Modified:
    llvm/trunk/lib/Target/ARM/ARMISelLowering.cpp
    llvm/trunk/test/CodeGen/ARM/vdup.ll

Modified: llvm/trunk/lib/Target/ARM/ARMISelLowering.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/ARM/ARMISelLowering.cpp?rev=246594&r1=246593&r2=246594&view=diff
==============================================================================
--- llvm/trunk/lib/Target/ARM/ARMISelLowering.cpp (original)
+++ llvm/trunk/lib/Target/ARM/ARMISelLowering.cpp Tue Sep  1 16:56:00 2015
@@ -5554,6 +5554,10 @@ SDValue ARMTargetLowering::ReconstructSh
       // 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.

Modified: llvm/trunk/test/CodeGen/ARM/vdup.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/ARM/vdup.ll?rev=246594&r1=246593&r2=246594&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/ARM/vdup.ll (original)
+++ llvm/trunk/test/CodeGen/ARM/vdup.ll Tue Sep  1 16:56:00 2015
@@ -364,3 +364,19 @@ define <4 x float> @check_spr_splat4_lan
   %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
+}