From b5740105d270a2d76da8812cafb63e4b799ada73 Mon Sep 17 00:00:00 2001
From: Eli Friedman <efriedma@quicinc.com>
Date: Wed, 20 May 2020 15:08:36 -0700
Subject: [PATCH] [BitcodeReader] Fix DelayedShuffle handling for ConstantExpr
 shuffles.

The indexing was messed up, so the result was completely broken.

Shuffle constant exprs are rare in practice; without vscale types,
constant folding generally elminates them. So sort of hard to trip over.

Fixes regression from D72467.

Differential Revision: https://reviews.llvm.org/D80330
---
 llvm/lib/Bitcode/Reader/BitcodeReader.cpp | 18 +++++++++++-------
 llvm/test/Bitcode/vscale-shuffle.ll       | 10 ++++++++++
 2 files changed, 21 insertions(+), 7 deletions(-)
 create mode 100644 llvm/test/Bitcode/vscale-shuffle.ll

diff --git a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
index a428416244f9..1ee9f7b7a50c 100644
--- a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -2337,6 +2337,7 @@ Error BitcodeReader::parseConstants() {
     uint64_t Op0Idx;
     uint64_t Op1Idx;
     uint64_t Op2Idx;
+    unsigned CstNo;
   };
   std::vector<DelayedShufTy> DelayedShuffles;
   while (true) {
@@ -2350,9 +2351,6 @@ Error BitcodeReader::parseConstants() {
     case BitstreamEntry::Error:
       return error("Malformed block");
     case BitstreamEntry::EndBlock:
-      if (NextCstNo != ValueList.size())
-        return error("Invalid constant reference");
-
       // Once all the constants have been read, go through and resolve forward
       // references.
       //
@@ -2365,6 +2363,7 @@ Error BitcodeReader::parseConstants() {
         uint64_t Op0Idx = DelayedShuffle.Op0Idx;
         uint64_t Op1Idx = DelayedShuffle.Op1Idx;
         uint64_t Op2Idx = DelayedShuffle.Op2Idx;
+        uint64_t CstNo = DelayedShuffle.CstNo;
         Constant *Op0 = ValueList.getConstantFwdRef(Op0Idx, OpTy);
         Constant *Op1 = ValueList.getConstantFwdRef(Op1Idx, OpTy);
         Type *ShufTy =
@@ -2375,9 +2374,12 @@ Error BitcodeReader::parseConstants() {
         SmallVector<int, 16> Mask;
         ShuffleVectorInst::getShuffleMask(Op2, Mask);
         Value *V = ConstantExpr::getShuffleVector(Op0, Op1, Mask);
-        ValueList.assignValue(V, NextCstNo, DelayedShuffle.CurFullTy);
-        ++NextCstNo;
+        ValueList.assignValue(V, CstNo, DelayedShuffle.CurFullTy);
       }
+
+      if (NextCstNo != ValueList.size())
+        return error("Invalid constant reference");
+
       ValueList.resolveConstantForwardRefs();
       return Error::success();
     case BitstreamEntry::Record:
@@ -2733,7 +2735,8 @@ Error BitcodeReader::parseConstants() {
       if (Record.size() < 3 || !OpTy)
         return error("Invalid record");
       DelayedShuffles.push_back(
-          {OpTy, OpTy, CurFullTy, Record[0], Record[1], Record[2]});
+          {OpTy, OpTy, CurFullTy, Record[0], Record[1], Record[2], NextCstNo});
+      ++NextCstNo;
       continue;
     }
     case bitc::CST_CODE_CE_SHUFVEC_EX: { // [opty, opval, opval, opval]
@@ -2743,7 +2746,8 @@ Error BitcodeReader::parseConstants() {
       if (Record.size() < 4 || !RTy || !OpTy)
         return error("Invalid record");
       DelayedShuffles.push_back(
-          {OpTy, RTy, CurFullTy, Record[1], Record[2], Record[3]});
+          {OpTy, RTy, CurFullTy, Record[1], Record[2], Record[3], NextCstNo});
+      ++NextCstNo;
       continue;
     }
     case bitc::CST_CODE_CE_CMP: {     // CE_CMP: [opty, opval, opval, pred]
diff --git a/llvm/test/Bitcode/vscale-shuffle.ll b/llvm/test/Bitcode/vscale-shuffle.ll
new file mode 100644
index 000000000000..3f36209c7aaf
--- /dev/null
+++ b/llvm/test/Bitcode/vscale-shuffle.ll
@@ -0,0 +1,10 @@
+; RUN: llvm-as < %s | llvm-dis -disable-output
+; RUN: verify-uselistorder < %s
+
+define void @f() {
+  %l = call <vscale x 16 x i8> @l(<vscale x 16 x i1> shufflevector (<vscale x 16 x i1> insertelement (<vscale x 16 x i1> undef, i1 true, i32 0), <vscale x 16 x i1> undef, <vscale x 16 x i32> zeroinitializer))
+  %i = add <vscale x 2 x i64> undef, shufflevector (<vscale x 2 x i64> insertelement (<vscale x 2 x i64> undef, i64 1, i32 0), <vscale x 2 x i64> undef, <vscale x 2 x i32> zeroinitializer)
+  unreachable
+}
+
+declare <vscale x 16 x i8> @l(<vscale x 16 x i1>)