[SLP] Match poison as instruction with the same opcode

Patch allows to vector scalar instruction + poison values as if poisons
are instructions with the same opcode. It allows better vectorization of
the repeated values, reduces number of insertelement instructions and
serves as a base ground for copyable elements vectorization

AVX512, -O3 + LTO

JM/ldecod - better vector code
Applications/oggenc - better vectorization
CINT2017speed/625.x264_s
CINT2017rate/525.x264_r - better vector code
CFP2017rate/526.blender_r - better vector code
CFP2006/447.dealII - small variations
Benchmarks/Bullet - extra vector code
CFP2017rate/510.parest_r - better vectorization
CINT2017rate/502.gcc_r
CINT2017speed/602.gcc_s - extra vector code
Benchmarks/tramp3d-v4 - small variations
CFP2006/453.povray - extra vector code
JM/lencod - better vector code
CFP2017rate/511.povray_r - extra vector code
MemFunctions/MemFunctions - extra vector code
LoopVectorization/LoopVectorizationBenchmarks - extra vector code
XRay/FDRMode - extra vector code
XRay/ReturnReference - extra vector code
LCALS/SubsetCLambdaLoops - extra vector code
LCALS/SubsetCRawLoops - extra vector code
LCALS/SubsetARawLoops - extra vector code
LCALS/SubsetALambdaLoops - extra vector code
DOE-ProxyApps-C++/miniFE - extra vector code
LoopVectorization/LoopInterleavingBenchmarks - extra vector code
LCALS/SubsetBLambdaLoops - extra vector code
MicroBenchmarks/harris - extra vector code
ImageProcessing/Dither - extra vector code
MicroBenchmarks/SLPVectorization - extra vector code
ImageProcessing/Blur - extra vector code
ImageProcessing/Dilate - extra vector code
Builtins/Int128 - extra vector code
ImageProcessing/Interpolation - extra vector code
ImageProcessing/BilateralFiltering - extra vector code
ImageProcessing/AnisotropicDiffusion - extra vector code
MicroBenchmarks/LoopInterchange - extra code vectorized
LCALS/SubsetBRawLoops - extra code vectorized
CINT2006/464.h264ref - extra vectorization with wider vectors
CFP2017rate/508.namd_r - small variations, extra phis vectorized
CFP2006/444.namd - 2 2 x phi replaced by 4 x phi
DOE-ProxyApps-C/SimpleMOC - extra code vectorized
CINT2017rate/541.leela_r
CINT2017speed/641.leela_s - the function better vectorized and inlined
Benchmarks/Misc/oourafft - 2 4 x bit reductions replaced by 2 x vector code
FreeBench/fourinarow - better vectorization

Reviewers: RKSimon

Reviewed By: RKSimon

Pull Request: llvm#115946

Author: alexey-bataev

llvm/include/llvm/IR/Instruction.h

@@ -278,6 +278,7 @@ class Instruction : public User,
   bool isUnaryOp() const { return isUnaryOp(getOpcode()); }
   bool isBinaryOp() const { return isBinaryOp(getOpcode()); }
   bool isIntDivRem() const { return isIntDivRem(getOpcode()); }
+  bool isFPDivRem() const { return isFPDivRem(getOpcode()); }
   bool isShift() const { return isShift(getOpcode()); }
   bool isCast() const { return isCast(getOpcode()); }
   bool isFuncletPad() const { return isFuncletPad(getOpcode()); }
@@ -304,6 +305,10 @@ class Instruction : public User,
     return Opcode == UDiv || Opcode == SDiv || Opcode == URem || Opcode == SRem;
   }
 
+  static inline bool isFPDivRem(unsigned Opcode) {
+    return Opcode == FDiv || Opcode == FRem;
+  }
+
   /// Determine if the Opcode is one of the shift instructions.
   static inline bool isShift(unsigned Opcode) {
     return Opcode >= Shl && Opcode <= AShr;