[X86] Allow pack instructions to be used for 512->256 truncates when -mprefer-vector-width=256 is causing 512-bit vectors to be split

If we're splitting the 512-bit vector anyway and we have zero/sign bits, then we might as well use pack instructions to concat and truncate at once.

Differential Revision: https://reviews.llvm.org/D65904

llvm-svn: 368210

2 files changed, 22 insertions, 22 deletions

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index e18b55b9629..368f409394e 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -40898,8 +40898,8 @@ static SDValue combineVectorTruncation(SDNode *N, SelectionDAG &DAG,
 static SDValue combineVectorSignBitsTruncation(SDNode *N, const SDLoc &DL,
                                                SelectionDAG &DAG,
                                                const X86Subtarget &Subtarget) {
-  // Requires SSE2 but AVX512 has fast truncate.
-  if (!Subtarget.hasSSE2() || Subtarget.hasAVX512())
+  // Requires SSE2.
+  if (!Subtarget.hasSSE2())
     return SDValue();
 
   if (!N->getValueType(0).isVector() || !N->getValueType(0).isSimple())
@@ -40923,6 +40923,13 @@ static SDValue combineVectorSignBitsTruncation(SDNode *N, const SDLoc &DL,
   if (InSVT != MVT::i16 && InSVT != MVT::i32 && InSVT != MVT::i64)
     return SDValue();
 
+  // AVX512 has fast truncate, but if the input is already going to be split,
+  // there's no harm in trying pack.
+  if (Subtarget.hasAVX512() &&
+      !(!Subtarget.useAVX512Regs() && VT.is256BitVector() &&
+        InVT.is512BitVector()))
+    return SDValue();
+
   unsigned NumPackedSignBits = std::min<unsigned>(SVT.getSizeInBits(), 16);
   unsigned NumPackedZeroBits = Subtarget.hasSSE41() ? NumPackedSignBits : 8;
 
diff --git a/llvm/test/CodeGen/X86/min-legal-vector-width.ll b/llvm/test/CodeGen/X86/min-legal-vector-width.ll
index b75fd2d8e05..40d557afe2b 100644
--- a/llvm/test/CodeGen/X86/min-legal-vector-width.ll
+++ b/llvm/test/CodeGen/X86/min-legal-vector-width.ll
@@ -757,9 +757,8 @@ define <8 x i32> @trunc_v8i64_v8i32_zeroes(<8 x i64>* %x) nounwind "min-legal-ve
 ; CHECK:       # %bb.0:
 ; CHECK-NEXT:    vpsrlq $48, 32(%rdi), %ymm0
 ; CHECK-NEXT:    vpsrlq $48, (%rdi), %ymm1
-; CHECK-NEXT:    vpmovqd %ymm1, %xmm1
-; CHECK-NEXT:    vpmovqd %ymm0, %xmm0
-; CHECK-NEXT:    vinserti128 $1, %xmm0, %ymm1, %ymm0
+; CHECK-NEXT:    vpackusdw %ymm0, %ymm1, %ymm0
+; CHECK-NEXT:    vpermq {{.*#+}} ymm0 = ymm0[0,2,1,3]
 ; CHECK-NEXT:    retq
   %a = load <8 x i64>, <8 x i64>* %x
   %b = lshr <8 x i64> %a, <i64 48, i64 48, i64 48, i64 48, i64 48, i64 48, i64 48, i64 48>
@@ -770,11 +769,9 @@ define <8 x i32> @trunc_v8i64_v8i32_zeroes(<8 x i64>* %x) nounwind "min-legal-ve
 define <16 x i16> @trunc_v16i32_v16i16_zeroes(<16 x i32>* %x) nounwind "min-legal-vector-width"="256" {
 ; CHECK-LABEL: trunc_v16i32_v16i16_zeroes:
 ; CHECK:       # %bb.0:
-; CHECK-NEXT:    vpsrld $16, 32(%rdi), %ymm0
-; CHECK-NEXT:    vpsrld $16, (%rdi), %ymm1
-; CHECK-NEXT:    vpmovdw %ymm1, %xmm1
-; CHECK-NEXT:    vpmovdw %ymm0, %xmm0
-; CHECK-NEXT:    vinserti128 $1, %xmm0, %ymm1, %ymm0
+; CHECK-NEXT:    vmovdqa (%rdi), %ymm1
+; CHECK-NEXT:    vmovdqa {{.*#+}} ymm0 = [1,3,5,7,9,11,13,15,17,19,21,23,25,27,29,31]
+; CHECK-NEXT:    vpermi2w 32(%rdi), %ymm1, %ymm0
 ; CHECK-NEXT:    retq
   %a = load <16 x i32>, <16 x i32>* %x
   %b = lshr <16 x i32> %a, <i32 16, i32 16, i32 16, i32 16, i32 16, i32 16, i32 16, i32 16, i32 16, i32 16, i32 16, i32 16, i32 16, i32 16, i32 16, i32 16>
@@ -787,9 +784,8 @@ define <32 x i8> @trunc_v32i16_v32i8_zeroes(<32 x i16>* %x) nounwind "min-legal-
 ; CHECK:       # %bb.0:
 ; CHECK-NEXT:    vpsrlw $8, 32(%rdi), %ymm0
 ; CHECK-NEXT:    vpsrlw $8, (%rdi), %ymm1
-; CHECK-NEXT:    vpmovwb %ymm1, %xmm1
-; CHECK-NEXT:    vpmovwb %ymm0, %xmm0
-; CHECK-NEXT:    vinserti128 $1, %xmm0, %ymm1, %ymm0
+; CHECK-NEXT:    vpackuswb %ymm0, %ymm1, %ymm0
+; CHECK-NEXT:    vpermq {{.*#+}} ymm0 = ymm0[0,2,1,3]
 ; CHECK-NEXT:    retq
   %a = load <32 x i16>, <32 x i16>* %x
   %b = lshr <32 x i16> %a, <i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8>
@@ -802,9 +798,8 @@ define <8 x i32> @trunc_v8i64_v8i32_sign(<8 x i64>* %x) nounwind "min-legal-vect
 ; CHECK:       # %bb.0:
 ; CHECK-NEXT:    vpsraq $48, 32(%rdi), %ymm0
 ; CHECK-NEXT:    vpsraq $48, (%rdi), %ymm1
-; CHECK-NEXT:    vpmovqd %ymm1, %xmm1
-; CHECK-NEXT:    vpmovqd %ymm0, %xmm0
-; CHECK-NEXT:    vinserti128 $1, %xmm0, %ymm1, %ymm0
+; CHECK-NEXT:    vpackssdw %ymm0, %ymm1, %ymm0
+; CHECK-NEXT:    vpermq {{.*#+}} ymm0 = ymm0[0,2,1,3]
 ; CHECK-NEXT:    retq
   %a = load <8 x i64>, <8 x i64>* %x
   %b = ashr <8 x i64> %a, <i64 48, i64 48, i64 48, i64 48, i64 48, i64 48, i64 48, i64 48>
@@ -817,9 +812,8 @@ define <16 x i16> @trunc_v16i32_v16i16_sign(<16 x i32>* %x) nounwind "min-legal-
 ; CHECK:       # %bb.0:
 ; CHECK-NEXT:    vpsrad $16, 32(%rdi), %ymm0
 ; CHECK-NEXT:    vpsrad $16, (%rdi), %ymm1
-; CHECK-NEXT:    vpmovdw %ymm1, %xmm1
-; CHECK-NEXT:    vpmovdw %ymm0, %xmm0
-; CHECK-NEXT:    vinserti128 $1, %xmm0, %ymm1, %ymm0
+; CHECK-NEXT:    vpackssdw %ymm0, %ymm1, %ymm0
+; CHECK-NEXT:    vpermq {{.*#+}} ymm0 = ymm0[0,2,1,3]
 ; CHECK-NEXT:    retq
   %a = load <16 x i32>, <16 x i32>* %x
   %b = ashr <16 x i32> %a, <i32 16, i32 16, i32 16, i32 16, i32 16, i32 16, i32 16, i32 16, i32 16, i32 16, i32 16, i32 16, i32 16, i32 16, i32 16, i32 16>
@@ -832,9 +826,8 @@ define <32 x i8> @trunc_v32i16_v32i8_sign(<32 x i16>* %x) nounwind "min-legal-ve
 ; CHECK:       # %bb.0:
 ; CHECK-NEXT:    vpsraw $8, 32(%rdi), %ymm0
 ; CHECK-NEXT:    vpsraw $8, (%rdi), %ymm1
-; CHECK-NEXT:    vpmovwb %ymm1, %xmm1
-; CHECK-NEXT:    vpmovwb %ymm0, %xmm0
-; CHECK-NEXT:    vinserti128 $1, %xmm0, %ymm1, %ymm0
+; CHECK-NEXT:    vpacksswb %ymm0, %ymm1, %ymm0
+; CHECK-NEXT:    vpermq {{.*#+}} ymm0 = ymm0[0,2,1,3]
 ; CHECK-NEXT:    retq
   %a = load <32 x i16>, <32 x i16>* %x
   %b = ashr <32 x i16> %a, <i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8, i16 8>