[mips] Correct lowering of VECTOR_SHUFFLE to VSHF.

Summary:
VECTOR_SHUFFLE concatenates the vectors in an vectorwise fashion.
  <0b00, 0b01> + <0b10, 0b11> -> <0b00, 0b01, 0b10, 0b11>
VSHF concatenates the vectors in a bitwise fashion:
  <0b00, 0b01> + <0b10, 0b11> ->
  0b0100       + 0b1110       -> 0b01001110
                                 <0b10, 0b11, 0b00, 0b01>
We must therefore swap the operands to get the correct result.

The test case that discovered the issue was MultiSource/Benchmarks/nbench.

Reviewers: matheusalmeida

Reviewed By: matheusalmeida

Differential Revision: http://llvm-reviews.chandlerc.com/D3142

llvm-svn: 204480

2 files changed, 20 insertions, 5 deletions

diff --git a/llvm/lib/Target/Mips/MipsSEISelLowering.cpp b/llvm/lib/Target/Mips/MipsSEISelLowering.cpp
index c40426d0e20..2fe5714e841 100644
--- a/llvm/lib/Target/Mips/MipsSEISelLowering.cpp
+++ b/llvm/lib/Target/Mips/MipsSEISelLowering.cpp
@@ -2566,7 +2566,14 @@ static SDValue lowerVECTOR_SHUFFLE_VSHF(SDValue Op, EVT ResTy,
   else
     llvm_unreachable("shuffle vector mask references neither vector operand?");
 
-  return DAG.getNode(MipsISD::VSHF, DL, ResTy, MaskVec, Op0, Op1);
+  // VECTOR_SHUFFLE concatenates the vectors in an vectorwise fashion.
+  // <0b00, 0b01> + <0b10, 0b11> -> <0b00, 0b01, 0b10, 0b11>
+  // VSHF concatenates the vectors in a bitwise fashion:
+  // <0b00, 0b01> + <0b10, 0b11> ->
+  // 0b0100       + 0b1110       -> 0b01001110
+  //                                <0b10, 0b11, 0b00, 0b01>
+  // We must therefore swap the operands to get the correct result.
+  return DAG.getNode(MipsISD::VSHF, DL, ResTy, MaskVec, Op1, Op0);
 }
 
 // Lower VECTOR_SHUFFLE into one of a number of instructions depending on the
diff --git a/llvm/test/CodeGen/Mips/msa/shuffle.ll b/llvm/test/CodeGen/Mips/msa/shuffle.ll
index 81aefbcace1..faeec5d58dd 100644
--- a/llvm/test/CodeGen/Mips/msa/shuffle.ll
+++ b/llvm/test/CodeGen/Mips/msa/shuffle.ll
@@ -58,7 +58,9 @@ define void @vshf_v16i8_3(<16 x i8>* %c, <16 x i8>* %a, <16 x i8>* %b) nounwind
   %3 = shufflevector <16 x i8> %1, <16 x i8> %2, <16 x i32> <i32 17, i32 24, i32 25, i32 18, i32 19, i32 20, i32 28, i32 19, i32 1, i32 8, i32 9, i32 2, i32 3, i32 4, i32 12, i32 3>
   ; CHECK-DAG: addiu [[PTR_A:\$[0-9]+]], {{.*}}, %lo($
   ; CHECK-DAG: ld.b [[R3:\$w[0-9]+]], 0([[PTR_A]])
-  ; CHECK-DAG: vshf.b [[R3]], [[R1]], [[R2]]
+  ; The concatenation step of vshf is bitwise not vectorwise so we must reverse
+  ; the operands to get the right answer.
+  ; CHECK-DAG: vshf.b [[R3]], [[R2]], [[R1]]
   store <16 x i8> %3, <16 x i8>* %c
   ; CHECK-DAG: st.b [[R3]], 0($4)
 
@@ -137,7 +139,9 @@ define void @vshf_v8i16_3(<8 x i16>* %c, <8 x i16>* %a, <8 x i16>* %b) nounwind
   %3 = shufflevector <8 x i16> %1, <8 x i16> %2, <8 x i32> <i32 1, i32 8, i32 9, i32 2, i32 3, i32 4, i32 12, i32 3>
   ; CHECK-DAG: addiu [[PTR_A:\$[0-9]+]], {{.*}}, %lo($
   ; CHECK-DAG: ld.h [[R3:\$w[0-9]+]], 0([[PTR_A]])
-  ; CHECK-DAG: vshf.h [[R3]], [[R1]], [[R2]]
+  ; The concatenation step of vshf is bitwise not vectorwise so we must reverse
+  ; the operands to get the right answer.
+  ; CHECK-DAG: vshf.h [[R3]], [[R2]], [[R1]]
   store <8 x i16> %3, <8 x i16>* %c
   ; CHECK-DAG: st.h [[R3]], 0($4)
 
@@ -215,7 +219,9 @@ define void @vshf_v4i32_3(<4 x i32>* %c, <4 x i32>* %a, <4 x i32>* %b) nounwind
   %3 = shufflevector <4 x i32> %1, <4 x i32> %2, <4 x i32> <i32 1, i32 5, i32 6, i32 4>
   ; CHECK-DAG: addiu [[PTR_A:\$[0-9]+]], {{.*}}, %lo($
   ; CHECK-DAG: ld.w [[R3:\$w[0-9]+]], 0([[PTR_A]])
-  ; CHECK-DAG: vshf.w [[R3]], [[R1]], [[R2]]
+  ; The concatenation step of vshf is bitwise not vectorwise so we must reverse
+  ; the operands to get the right answer.
+  ; CHECK-DAG: vshf.w [[R3]], [[R2]], [[R1]]
   store <4 x i32> %3, <4 x i32>* %c
   ; CHECK-DAG: st.w [[R3]], 0($4)
 
@@ -294,7 +300,9 @@ define void @vshf_v2i64_3(<2 x i64>* %c, <2 x i64>* %a, <2 x i64>* %b) nounwind
   %3 = shufflevector <2 x i64> %1, <2 x i64> %2, <2 x i32> <i32 1, i32 2>
   ; CHECK-DAG: addiu [[PTR_A:\$[0-9]+]], {{.*}}, %lo($
   ; CHECK-DAG: ld.d [[R3:\$w[0-9]+]], 0([[PTR_A]])
-  ; CHECK-DAG: vshf.d [[R3]], [[R1]], [[R2]]
+  ; The concatenation step of vshf is bitwise not vectorwise so we must reverse
+  ; the operands to get the right answer.
+  ; CHECK-DAG: vshf.d [[R3]], [[R2]], [[R1]]
   store <2 x i64> %3, <2 x i64>* %c
   ; CHECK-DAG: st.d [[R3]], 0($4)