[LLVM][IR] Use splat syntax when printing ConstantExpr based splats.

Author: paulwalker-arm

llvm/lib/IR/AsmWriter.cpp

@@ -1741,6 +1741,24 @@ static void WriteConstantInternal(raw_ostream &Out, const Constant *CV,
   }
 
   if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(CV)) {
+    // Use the same shorthand for splat vector (i.e. "splat(Ty val)") as is
+    // permitted on IR input to reduce the output changes when enabling
+    // UseConstant{Int,FP}ForScalableSplat.
+    // TODO: Remove this block when the UseConstant{Int,FP}ForScalableSplat
+    // options are removed.
+    if (CE->getOpcode() == Instruction::ShuffleVector) {
+      if (auto *SplatVal = CE->getSplatValue()) {
+        if (isa<ConstantInt>(SplatVal) || isa<ConstantFP>(SplatVal)) {
+          Out << "splat (";
+          WriterCtx.TypePrinter->print(SplatVal->getType(), Out);
+          Out << ' ';
+          WriteAsOperandInternal(Out, SplatVal, WriterCtx);
+          Out << ')';
+          return;
+        }
+      }
+    }
+
     Out << CE->getOpcodeName();
     WriteOptimizationInfo(Out, CE);
     Out << " (";