[llvm] cc77da5 - [X86] LowerTRUNCATE - use LowerTruncateVecPackWithSignBits for prefer-256 bit AVX512 cases during type legalization

[Simon Pilgrim via llvm-commits]

Author: Simon Pilgrim
Date: 2023-07-20T13:55:28+01:00
New Revision: cc77da50204b993dd68b717cfb1fb6c3d10045c5

URL: https://github.com/llvm/llvm-project/commit/cc77da50204b993dd68b717cfb1fb6c3d10045c5
DIFF: https://github.com/llvm/llvm-project/commit/cc77da50204b993dd68b717cfb1fb6c3d10045c5.diff

LOG: [X86] LowerTRUNCATE - use LowerTruncateVecPackWithSignBits for prefer-256 bit AVX512 cases during type legalization

If the AVX512 target will split the 512-bit vector truncation then try to use PACKSS/PACKUS first.

Added: 
    

Modified: 
    llvm/lib/Target/X86/X86ISelLowering.cpp
    llvm/test/CodeGen/X86/min-legal-vector-width.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 2c65984d706567..44654a804d5505 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -23113,14 +23113,16 @@ SDValue X86TargetLowering::LowerTRUNCATE(SDValue Op, SelectionDAG &DAG) const {
       return DAG.getNode(ISD::CONCAT_VECTORS, DL, VT, Lo, Hi);
     }
 
-    // Pre-AVX512 see if we can make use of PACKSS/PACKUS.
-    if (!Subtarget.hasAVX512()) {
+    // Pre-AVX512 (or prefer-256bit) see if we can make use of PACKSS/PACKUS.
+    if (!Subtarget.hasAVX512() ||
+        (InVT.is512BitVector() && VT.is256BitVector()))
       if (SDValue SignPack =
               LowerTruncateVecPackWithSignBits(VT, In, DL, Subtarget, DAG))
         return SignPack;
 
+    // Pre-AVX512 see if we can make use of PACKSS/PACKUS.
+    if (!Subtarget.hasAVX512())
       return LowerTruncateVecPack(VT, In, DL, Subtarget, DAG);
-    }
 
     // Otherwise let default legalization handle it.
     return SDValue();

diff  --git a/llvm/test/CodeGen/X86/min-legal-vector-width.ll b/llvm/test/CodeGen/X86/min-legal-vector-width.ll
index 8dffb2c8559264..7dd4af76897929 100644
--- a/llvm/test/CodeGen/X86/min-legal-vector-width.ll
+++ b/llvm/test/CodeGen/X86/min-legal-vector-width.ll
@@ -1186,9 +1186,8 @@ 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>