From 1ee6ec2bf370fbd1d93f34c8b56741a9d3f22ed2 Mon Sep 17 00:00:00 2001
From: Eli Friedman <efriedma@quicinc.com>
Date: Tue, 31 Mar 2020 13:08:59 -0700
Subject: Remove "mask" operand from shufflevector.

Instead, represent the mask as out-of-line data in the instruction. This
should be more efficient in the places that currently use
getShuffleVector(), and paves the way for further changes to add new
shuffles for scalable vectors.

This doesn't change the syntax in textual IR. And I don't currently plan
to change the bitcode encoding in this patch, although we'll probably
need to do something once we extend shufflevector for scalable types.

I expect that once this is finished, we can then replace the raw "mask"
with something more appropriate for scalable vectors.  Not sure exactly
what this looks like at the moment, but there are a few different ways
we could handle it.  Maybe we could try to describe specific shuffles.
Or maybe we could define it in terms of a function to convert a fixed-length
array into an appropriate scalable vector, using a "step", or something
like that.

Differential Revision: https://reviews.llvm.org/D72467
---
 llvm/lib/Bitcode/Reader/BitcodeReader.cpp | 52 ++++++++++++++++++++++---------
 1 file changed, 38 insertions(+), 14 deletions(-)

(limited to 'llvm/lib/Bitcode/Reader/BitcodeReader.cpp')

diff --git a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
index de2a6b4..16d3b79 100644
--- a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -2337,6 +2337,15 @@ Error BitcodeReader::parseConstants() {
   Type *CurFullTy = Type::getInt32Ty(Context);
   unsigned NextCstNo = ValueList.size();
 
+  struct DelayedShufTy {
+    VectorType *OpTy;
+    VectorType *RTy;
+    Type *CurFullTy;
+    uint64_t Op0Idx;
+    uint64_t Op1Idx;
+    uint64_t Op2Idx;
+  };
+  std::vector<DelayedShufTy> DelayedShuffles;
   while (true) {
     Expected<BitstreamEntry> MaybeEntry = Stream.advanceSkippingSubblocks();
     if (!MaybeEntry)
@@ -2353,6 +2362,29 @@ Error BitcodeReader::parseConstants() {
 
       // Once all the constants have been read, go through and resolve forward
       // references.
+      //
+      // We have to treat shuffles specially because they don't have three
+      // operands anymore.  We need to convert the shuffle mask into an array,
+      // and we can't convert a forward reference.
+      for (auto &DelayedShuffle : DelayedShuffles) {
+        VectorType *OpTy = DelayedShuffle.OpTy;
+        VectorType *RTy = DelayedShuffle.RTy;
+        uint64_t Op0Idx = DelayedShuffle.Op0Idx;
+        uint64_t Op1Idx = DelayedShuffle.Op1Idx;
+        uint64_t Op2Idx = DelayedShuffle.Op2Idx;
+        Constant *Op0 = ValueList.getConstantFwdRef(Op0Idx, OpTy);
+        Constant *Op1 = ValueList.getConstantFwdRef(Op1Idx, OpTy);
+        Type *ShufTy =
+            VectorType::get(Type::getInt32Ty(Context), RTy->getElementCount());
+        Constant *Op2 = ValueList.getConstantFwdRef(Op2Idx, ShufTy);
+        if (!ShuffleVectorInst::isValidOperands(Op0, Op1, Op2))
+          return error("Invalid shufflevector operands");
+        SmallVector<int, 16> Mask;
+        ShuffleVectorInst::getShuffleMask(Op2, Mask);
+        Value *V = ConstantExpr::getShuffleVector(Op0, Op1, Mask);
+        ValueList.assignValue(V, NextCstNo, DelayedShuffle.CurFullTy);
+        ++NextCstNo;
+      }
       ValueList.resolveConstantForwardRefs();
       return Error::success();
     case BitstreamEntry::Record:
@@ -2694,13 +2726,9 @@ Error BitcodeReader::parseConstants() {
       VectorType *OpTy = dyn_cast<VectorType>(CurTy);
       if (Record.size() < 3 || !OpTy)
         return error("Invalid record");
-      Constant *Op0 = ValueList.getConstantFwdRef(Record[0], OpTy);
-      Constant *Op1 = ValueList.getConstantFwdRef(Record[1], OpTy);
-      Type *ShufTy = VectorType::get(Type::getInt32Ty(Context),
-                                     OpTy->getElementCount());
-      Constant *Op2 = ValueList.getConstantFwdRef(Record[2], ShufTy);
-      V = ConstantExpr::getShuffleVector(Op0, Op1, Op2);
-      break;
+      DelayedShuffles.push_back(
+          {OpTy, OpTy, CurFullTy, Record[0], Record[1], Record[2]});
+      continue;
     }
     case bitc::CST_CODE_CE_SHUFVEC_EX: { // [opty, opval, opval, opval]
       VectorType *RTy = dyn_cast<VectorType>(CurTy);
@@ -2708,13 +2736,9 @@ Error BitcodeReader::parseConstants() {
         dyn_cast_or_null<VectorType>(getTypeByID(Record[0]));
       if (Record.size() < 4 || !RTy || !OpTy)
         return error("Invalid record");
-      Constant *Op0 = ValueList.getConstantFwdRef(Record[1], OpTy);
-      Constant *Op1 = ValueList.getConstantFwdRef(Record[2], OpTy);
-      Type *ShufTy = VectorType::get(Type::getInt32Ty(Context),
-                                     RTy->getElementCount());
-      Constant *Op2 = ValueList.getConstantFwdRef(Record[3], ShufTy);
-      V = ConstantExpr::getShuffleVector(Op0, Op1, Op2);
-      break;
+      DelayedShuffles.push_back(
+          {OpTy, RTy, CurFullTy, Record[1], Record[2], Record[3]});
+      continue;
     }
     case bitc::CST_CODE_CE_CMP: {     // CE_CMP: [opty, opval, opval, pred]
       if (Record.size() < 4)
-- 
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