[PowerPC] Don't crash on larger splats that can be achieved through 1-byte splats

[nemanjai]

Summary

There's code in the back end to ensure that we leave nodes that are 1-byte splats as-is so that they'd match the XXSPLTISB instruction. However, the code doesn't handle a situation where the value being splat is a larger value that happens to have repeating bytes. This patch addresses those situation by adding v16i8 constant splat and bitcasting it to the target type.

This fixes PR33808.

[echristo]

Seems reasonable...

[nemanjai]

In D35650#815439, @echristo wrote:

Seems reasonable...

Is this an equivalent of a LGTM? :)

[hfinkel]

In D35650#828815, @nemanjai wrote:

In D35650#815439, @echristo wrote:

Seems reasonable...

Is this an equivalent of a LGTM? :)

LGTM (too).

[echristo]

Yep.

llvm/trunk/lib/Target/PowerPC/PPCISelLowering.cpp

if (Subtarget.hasP9Vector() && SplatSize == 1) {
     if (HasAnyUndefs || ISD::isBuildVectorAllOnes(BVN)) {
       SmallVector<SDValue, 16> Ops(16, DAG.getConstant(SplatBits,
                                                        dl, MVT::i32));
       SDValue NewBV = DAG.getBuildVector(MVT::v16i8, dl, Ops);
       if (Op.getValueType() != MVT::v16i8)
         return DAG.getBitcast(Op.getValueType(), NewBV);
       return NewBV;
     }
+
+    // BuildVectorSDNode::isConstantSplat() is actually pretty smart. It'll
+    // detect that constant splats like v8i16: 0xABAB are really just splats
+    // of a 1-byte constant. In this case, we need to convert the node to a
+    // splat of v16i8 and a bitcast.
+    if (Op.getValueType() != MVT::v16i8)
+      return DAG.getBitcast(Op.getValueType(),
+                            DAG.getConstant(SplatBits, dl, MVT::v16i8));
+
     return Op;
   }
 
   // If the sign extended value is in the range [-16,15], use VSPLTI[bhw].
   int32_t SextVal= (int32_t(SplatBits << (32-SplatBitSize)) >>
                     (32-SplatBitSize));
   if (SextVal >= -16 && SextVal <= 15)
     return BuildSplatI(SextVal, SplatSize, Op.getValueType(), DAG, dl);

llvm/trunk/test/CodeGen/PowerPC/splat-larger-types-as-v16i8.ll

+; RUN: llc -mcpu=pwr9 -mtriple=powerpc64-unknown-unknown < %s | FileCheck %s
+; RUN: llc -mcpu=pwr9 -mtriple=powerpc64le-unknown-unknown < %s | FileCheck %s
+define <8 x i16> @test1() {
+entry:
+  ret <8 x i16> <i16 257, i16 257, i16 257, i16 257, i16 257, i16 257, i16 257, i16 257>
+; CHECK-LABEL: test1
+; CHECK: xxspltib 34, 1
+}
+define <8 x i16> @testAB() {
+entry:
+; CHECK-LABEL: testAB
+; CHECK: xxspltib 34, 171
+  ret <8 x i16> <i16 43947, i16 43947, i16 43947, i16 43947, i16 43947, i16 43947, i16 43947, i16 43947>
+}
+define <4 x i32> @testAB32() {
+entry:
+; CHECK-LABEL: testAB32
+; CHECK: xxspltib 34, 171
+  ret <4 x i32> <i32 2880154539, i32 2880154539, i32 2880154539, i32 2880154539>
+}