From a60aa91374bbcafc0d032c3f4217637fc816b8bc Mon Sep 17 00:00:00 2001 From: Hans Wennborg Date: Mon, 1 Oct 2018 12:07:45 +0000 Subject: 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 --- .../InstCombine/InstCombineVectorOps.cpp | 46 +--------------------- 1 file changed, 2 insertions(+), 44 deletions(-) (limited to 'llvm/lib/Transforms') 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, 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 -- cgit v1.2.3