Revert r343407 "[InstCombine] try to convert vector insert+extract to trunc"

This caused Chromium builds to fail with "Illegal Trunc" assertion.
See https://crbug.com/890723 for repro.

> This transform is requested for the backend in:
> https://bugs.llvm.org/show_bug.cgi?id=39016
> ...but I figured it was worth doing in IR too, and it's probably
> easier to implement here, so that's this patch.
>
> In the simplest case, we are just truncating a scalar value. If the
> extract index doesn't correspond to the LSBs of the scalar, then we
> have to shift-right before the truncate. Endian-ness makes this tricky,
> but hopefully the ASCII-art helps visualize the transform.
>
> Differential Revision: https://reviews.llvm.org/D52439

llvm-svn: 343458

1 files changed, 2 insertions, 44 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp b/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
index ca29be097e6..c391034dc00 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
@@ -167,8 +167,7 @@ Instruction *InstCombiner::scalarizePHI(ExtractElementInst &EI, PHINode *PN) {
 }
 
 static Instruction *foldBitcastExtElt(ExtractElementInst &Ext,
-                                      InstCombiner::BuilderTy &Builder,
-                                      bool IsBigEndian) {
+                                      InstCombiner::BuilderTy &Builder) {
   Value *X;
   uint64_t ExtIndexC;
   if (!match(Ext.getVectorOperand(), m_BitCast(m_Value(X))) ||
@@ -187,47 +186,6 @@ static Instruction *foldBitcastExtElt(ExtractElementInst &Ext,
     if (Value *Elt = findScalarElement(X, ExtIndexC))
       return new BitCastInst(Elt, DestTy);
 
-  // If the source elements are wider than the destination, try to shift and
-  // truncate a subset of scalar bits of an insert op.
-  if (NumSrcElts < NumElts && SrcTy->getScalarType()->isIntegerTy()) {
-    Value *Scalar;
-    uint64_t InsIndexC;
-    if (!match(X, m_InsertElement(m_Value(), m_Value(Scalar),
-                                  m_ConstantInt(InsIndexC))))
-      return nullptr;
-
-    // The extract must be from the subset of vector elements that we inserted
-    // into. Example: if we inserted element 1 of a <2 x i64> and we are
-    // extracting an i16 (narrowing ratio = 4), then this extract must be from 1
-    // of elements 4-7 of the bitcasted vector.
-    unsigned NarrowingRatio = NumElts / NumSrcElts;
-    if (ExtIndexC / NarrowingRatio != InsIndexC)
-      return nullptr;
-
-    // We are extracting part of the original scalar. How that scalar is
-    // inserted into the vector depends on the endian-ness. Example:
-    //              Vector Byte Elt Index:    0  1  2  3  4  5  6  7
-    //                                       +--+--+--+--+--+--+--+--+
-    // inselt <2 x i32> V, <i32> S, 1:       |V0|V1|V2|V3|S0|S1|S2|S3|
-    // extelt <4 x i16> V', 3:               |                 |S2|S3|
-    //                                       +--+--+--+--+--+--+--+--+
-    // If this is little-endian, S2|S3 are the MSB of the 32-bit 'S' value.
-    // If this is big-endian, S2|S3 are the LSB of the 32-bit 'S' value.
-    // In this example, we must right-shift little-endian. Big-endian is just a
-    // truncate.
-    unsigned Chunk = ExtIndexC % NarrowingRatio;
-    if (IsBigEndian)
-      Chunk = NarrowingRatio - 1 - Chunk;
-    unsigned ShAmt = Chunk * DestTy->getPrimitiveSizeInBits();
-    if (ShAmt) {
-      // Bail out if we could end with more instructions than we started with.
-      if (!Ext.getVectorOperand()->hasOneUse())
-        return nullptr;
-      Scalar = Builder.CreateLShr(Scalar, ShAmt);
-    }
-    return new TruncInst(Scalar, DestTy);
-  }
-
   return nullptr;
 }
 
@@ -266,7 +224,7 @@ Instruction *InstCombiner::visitExtractElementInst(ExtractElementInst &EI) {
       }
     }
 
-    if (Instruction *I = foldBitcastExtElt(EI, Builder, DL.isBigEndian()))
+    if (Instruction *I = foldBitcastExtElt(EI, Builder))
       return I;
 
     // If there's a vector PHI feeding a scalar use through this extractelement