From 7c69a03c56601a55f47f29ea59e33c37e62db556 Mon Sep 17 00:00:00 2001
From: Eli Friedman <efriedma@quicinc.com>
Date: Fri, 6 Dec 2019 12:33:46 -0800
Subject: [PATCH] [ConstantFold][SVE] Fix constant folding for shufflevector.

Don't try to fold away shuffles which can't be folded.  Fix creation of
shufflevector constant expressions.

Differential Revision: https://reviews.llvm.org/D71147
---
 llvm/lib/IR/ConstantFold.cpp                        |  6 ++++++
 llvm/lib/IR/Constants.cpp                           |  2 +-
 llvm/lib/IR/ConstantsContext.h                      |  2 +-
 llvm/test/Analysis/ConstantFolding/shufflevector.ll | 11 +++++++++++
 4 files changed, 19 insertions(+), 2 deletions(-)
 create mode 100644 llvm/test/Analysis/ConstantFolding/shufflevector.ll

diff --git a/llvm/lib/IR/ConstantFold.cpp b/llvm/lib/IR/ConstantFold.cpp
index bf01f9f2ae6..6e24f03c4cf 100644
--- a/llvm/lib/IR/ConstantFold.cpp
+++ b/llvm/lib/IR/ConstantFold.cpp
@@ -873,6 +873,12 @@ Constant *llvm::ConstantFoldShuffleVectorInstruction(Constant *V1,
   // Don't break the bitcode reader hack.
   if (isa<ConstantExpr>(Mask)) return nullptr;
 
+  // Do not iterate on scalable vector. The num of elements is unknown at
+  // compile-time.
+  VectorType *ValTy = cast<VectorType>(V1->getType());
+  if (ValTy->isScalable())
+    return nullptr;
+
   unsigned SrcNumElts = V1->getType()->getVectorNumElements();
 
   // Loop over the shuffle mask, evaluating each element.
diff --git a/llvm/lib/IR/Constants.cpp b/llvm/lib/IR/Constants.cpp
index 7ea5cb8b167..fc215d6bf95 100644
--- a/llvm/lib/IR/Constants.cpp
+++ b/llvm/lib/IR/Constants.cpp
@@ -2211,7 +2211,7 @@ Constant *ConstantExpr::getShuffleVector(Constant *V1, Constant *V2,
   if (Constant *FC = ConstantFoldShuffleVectorInstruction(V1, V2, Mask))
     return FC;          // Fold a few common cases.
 
-  unsigned NElts = Mask->getType()->getVectorNumElements();
+  ElementCount NElts = Mask->getType()->getVectorElementCount();
   Type *EltTy = V1->getType()->getVectorElementType();
   Type *ShufTy = VectorType::get(EltTy, NElts);
 
diff --git a/llvm/lib/IR/ConstantsContext.h b/llvm/lib/IR/ConstantsContext.h
index 1ec9087551f..f5e2481f390 100644
--- a/llvm/lib/IR/ConstantsContext.h
+++ b/llvm/lib/IR/ConstantsContext.h
@@ -149,7 +149,7 @@ public:
   ShuffleVectorConstantExpr(Constant *C1, Constant *C2, Constant *C3)
   : ConstantExpr(VectorType::get(
                    cast<VectorType>(C1->getType())->getElementType(),
-                   cast<VectorType>(C3->getType())->getNumElements()),
+                   cast<VectorType>(C3->getType())->getElementCount()),
                  Instruction::ShuffleVector,
                  &Op<0>(), 3) {
     Op<0>() = C1;
diff --git a/llvm/test/Analysis/ConstantFolding/shufflevector.ll b/llvm/test/Analysis/ConstantFolding/shufflevector.ll
new file mode 100644
index 00000000000..d69c2caecc0
--- /dev/null
+++ b/llvm/test/Analysis/ConstantFolding/shufflevector.ll
@@ -0,0 +1,11 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -constprop -S | FileCheck %s
+
+define <vscale x 4 x i32> @shufflevector_scalable_constant() {
+; CHECK-LABEL: @shufflevector_scalable_constant(
+; CHECK-NEXT:    ret <vscale x 4 x i32> shufflevector (<vscale x 4 x i32> insertelement (<vscale x 4 x i32> undef, i32 1, i32 0), <vscale x 4 x i32> undef, <vscale x 4 x i32> zeroinitializer)
+;
+  %i = insertelement <vscale x 4 x i32> undef, i32 1, i32 0
+  %i2 = shufflevector <vscale x 4 x i32> %i, <vscale x 4 x i32> undef, <vscale x 4 x i32> zeroinitializer
+  ret <vscale x 4 x i32> %i2
+}