[llvm] a701dc5 - [PowerPC] Remove undefs from splat input when changing shuffle mask

[Nemanja Ivanovic via llvm-commits]

Author: Nemanja Ivanovic
Date: 2020-07-02T12:26:56-05:00
New Revision: a701dc5510ab8e977dcb797035475e641d6a353a

URL: https://github.com/llvm/llvm-project/commit/a701dc5510ab8e977dcb797035475e641d6a353a
DIFF: https://github.com/llvm/llvm-project/commit/a701dc5510ab8e977dcb797035475e641d6a353a.diff

LOG: [PowerPC] Remove undefs from splat input when changing shuffle mask

As of 1fed131660b2c5d3ea7007e273a7a5da80699445, we have code that
changes shuffle masks so that we can put the shuffle in a canonical
form that can be matched to a single instruction. However, it
does not properly account for undef elements in the BUILD_VECTOR
that is the RHS splat so we can end up with undefs where they
shouldn't be. This patch converts the splat input with undefs to
one without.

Added: 
    

Modified: 
    llvm/lib/Target/PowerPC/PPCISelLowering.cpp
    llvm/test/CodeGen/PowerPC/canonical-merge-shuffles.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
index 0743a5a4373b..6083a0d26dd8 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -14452,6 +14452,11 @@ SDValue PPCTargetLowering::combineVectorShuffle(ShuffleVectorSDNode *SVN,
     for (int i = 0, e = Mask.size(); i < e; i += 2)
       ShuffV[i] = (ShuffV[i + 1] + NumElts);
 
+  // If the RHS has undefs, we need to remove them since we may have created
+  // a shuffle that adds those instead of the splat value.
+  SDValue SplatVal = cast<BuildVectorSDNode>(RHS.getNode())->getSplatValue();
+  RHS = DAG.getSplatBuildVector(RHS.getValueType(), dl, SplatVal);
+
   Res = DAG.getVectorShuffle(SVN->getValueType(0), dl, LHS, RHS, ShuffV);
   return Res;
 }

diff  --git a/llvm/test/CodeGen/PowerPC/canonical-merge-shuffles.ll b/llvm/test/CodeGen/PowerPC/canonical-merge-shuffles.ll
index 6c7923cd94aa..53e48b185714 100644
--- a/llvm/test/CodeGen/PowerPC/canonical-merge-shuffles.ll
+++ b/llvm/test/CodeGen/PowerPC/canonical-merge-shuffles.ll
@@ -343,5 +343,37 @@ test_entry:
   unreachable
 }
 
+define dso_local <4 x i32> @replace_undefs_in_splat(<4 x i32> %a) local_unnamed_addr #0 {
+; CHECK-P8-LABEL: replace_undefs_in_splat:
+; CHECK-P8:       # %bb.0: # %entry
+; CHECK-P8-NEXT:    addis r3, r2, .LCPI14_0 at toc@ha
+; CHECK-P8-NEXT:    addi r3, r3, .LCPI14_0 at toc@l
+; CHECK-P8-NEXT:    lvx v3, 0, r3
+; CHECK-P8-NEXT:    vmrgow v2, v3, v2
+; CHECK-P8-NEXT:    blr
+;
+; CHECK-P9-LABEL: replace_undefs_in_splat:
+; CHECK-P9:       # %bb.0: # %entry
+; CHECK-P9-NEXT:    addis r3, r2, .LCPI14_0 at toc@ha
+; CHECK-P9-NEXT:    addi r3, r3, .LCPI14_0 at toc@l
+; CHECK-P9-NEXT:    lxvx v3, 0, r3
+; CHECK-P9-NEXT:    vmrgow v2, v3, v2
+; CHECK-P9-NEXT:    blr
+;
+; CHECK-NOVSX-LABEL: replace_undefs_in_splat:
+; CHECK-NOVSX:       # %bb.0: # %entry
+; CHECK-NOVSX-NEXT:    addis r3, r2, .LCPI14_0 at toc@ha
+; CHECK-NOVSX-NEXT:    addis r4, r2, .LCPI14_1 at toc@ha
+; CHECK-NOVSX-NEXT:    addi r3, r3, .LCPI14_0 at toc@l
+; CHECK-NOVSX-NEXT:    lvx v3, 0, r3
+; CHECK-NOVSX-NEXT:    addi r3, r4, .LCPI14_1 at toc@l
+; CHECK-NOVSX-NEXT:    lvx v4, 0, r3
+; CHECK-NOVSX-NEXT:    vperm v2, v4, v2, v3
+; CHECK-NOVSX-NEXT:    blr
+entry:
+  %vecins1 = shufflevector <4 x i32> %a, <4 x i32> <i32 undef, i32 566, i32 undef, i32 566>, <4 x i32> <i32 0, i32 5, i32 2, i32 7>
+  ret <4 x i32> %vecins1
+}
+
 declare double @dummy() local_unnamed_addr
 attributes #0 = { nounwind }