[SLP]Fix compiler crash when calculating extract cost for undefs.

[ABataev]

Summary

Need to add an extra check for potential undef values in
computeExtractCost function to avoid compiler crash on casting to
instructon.

[RKSimon]

LGTM

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

computeExtractCost(ArrayRef<Value *> VL, FixedVectorType *VecTy,
   InstructionCost Cost = 0;
 
   // Process extracts in blocks of EltsPerVector to check if the source vector
   // operand can be re-used directly. If not, add the cost of creating a shuffle
   // to extract the values into a vector register.
   for (auto *V : VL) {
     ++Idx;
 
+    // Need to exclude undefs from analysis.
+    if (isa<UndefValue>(V) || Mask[Idx] == UndefMaskElem)
+      continue;
+
     // Reached the start of a new vector registers.
     if (Idx % EltsPerVector == 0) {
       AllConsecutive = true;
       continue;
     }
 
     // Check all extracts for a vector register on the target directly
     // extract values in order.
     unsigned CurrentIdx = *getExtractIndex(cast<Instruction>(V));
+    if (!isa<UndefValue>(VL[Idx - 1]) && Mask[Idx - 1] != UndefMaskElem) {
       unsigned PrevIdx = *getExtractIndex(cast<Instruction>(VL[Idx - 1]));
       AllConsecutive &= PrevIdx + 1 == CurrentIdx &&
                         CurrentIdx % EltsPerVector == Idx % EltsPerVector;
+    }
 
     if (AllConsecutive)
       continue;
 
     // Skip all indices, except for the last index per vector block.
     if ((Idx + 1) % EltsPerVector != 0 && Idx + 1 != VL.size())
       continue;
 

llvm/test/Transforms/SLPVectorizer/X86/extracts-with-undefs.ll

+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -slp-vectorizer -S -mtriple=x86_64-unknown-linux-gnu | FileCheck %s
+
+define void @test() {
+; CHECK-LABEL: @test(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[BODY:%.*]]
+; CHECK:       body:
+; CHECK-NEXT:    [[TMP0:%.*]] = phi <2 x double> [ zeroinitializer, [[ENTRY:%.*]] ], [ zeroinitializer, [[BODY]] ]
+; CHECK-NEXT:    [[TMP1:%.*]] = extractelement <2 x double> [[TMP0]], i32 1
+; CHECK-NEXT:    [[TMP2:%.*]] = insertelement <2 x double> <double poison, double undef>, double [[TMP1]], i32 0
+; CHECK-NEXT:    [[TMP3:%.*]] = fmul fast <2 x double> [[TMP2]], zeroinitializer
+; CHECK-NEXT:    [[TMP4:%.*]] = extractelement <2 x double> [[TMP3]], i32 0
+; CHECK-NEXT:    [[TMP5:%.*]] = extractelement <2 x double> [[TMP3]], i32 1
+; CHECK-NEXT:    [[ADD8_I_I:%.*]] = fadd fast double [[TMP4]], [[TMP5]]
+; CHECK-NEXT:    [[CMP42_I:%.*]] = fcmp fast ole double [[ADD8_I_I]], 0.000000e+00
+; CHECK-NEXT:    br i1 false, label [[BODY]], label [[EXIT:%.*]]
+; CHECK:       exit:
+; CHECK-NEXT:    br i1 false, label [[IF_THEN135_I:%.*]], label [[IF_END209_I:%.*]]
+; CHECK:       if.then135.i:
+; CHECK-NEXT:    [[TMP6:%.*]] = fcmp fast olt <2 x double> [[TMP0]], zeroinitializer
+; CHECK-NEXT:    [[TMP7:%.*]] = extractelement <2 x i1> [[TMP6]], i32 0
+; CHECK-NEXT:    [[TMP8:%.*]] = insertelement <2 x i1> <i1 poison, i1 false>, i1 [[TMP7]], i32 0
+; CHECK-NEXT:    [[TMP9:%.*]] = select <2 x i1> [[TMP8]], <2 x double> zeroinitializer, <2 x double> zeroinitializer
+; CHECK-NEXT:    [[TMP10:%.*]] = fmul fast <2 x double> zeroinitializer, [[TMP9]]
+; CHECK-NEXT:    [[TMP11:%.*]] = fmul fast <2 x double> [[TMP10]], zeroinitializer
+; CHECK-NEXT:    [[TMP12:%.*]] = fadd fast <2 x double> [[TMP11]], zeroinitializer
+; CHECK-NEXT:    br label [[IF_END209_I]]
+; CHECK:       if.end209.i:
+; CHECK-NEXT:    [[TMP13:%.*]] = phi <2 x double> [ [[TMP12]], [[IF_THEN135_I]] ], [ zeroinitializer, [[EXIT]] ]
+; CHECK-NEXT:    ret void
+;
+entry:
+  br label %body
+
+body:
+  %phi1 = phi double [ 0.000000e+00, %entry ], [ 0.000000e+00, %body ]
+  %phi2 = phi double [ 0.000000e+00, %entry ], [ 0.000000e+00, %body ]
+  %mul.i478.i = fmul fast double %phi1, 0.000000e+00
+  %mul7.i485.i = fmul fast double undef, 0.000000e+00
+  %add8.i.i = fadd fast double %mul.i478.i, %mul7.i485.i
+  %cmp42.i = fcmp fast ole double %add8.i.i, 0.000000e+00
+  br i1 false, label %body, label %exit
+
+exit:
+  br i1 false, label %if.then135.i, label %if.end209.i
+
+if.then135.i:
+  %cmp145.i = fcmp fast olt double %phi1, 0.000000e+00
+  %0 = select i1 false, double 0.000000e+00, double 0.000000e+00
+  %cmp152.i = fcmp fast olt double %phi2, 0.000000e+00
+  %1 = select i1 %cmp152.i, double 0.000000e+00, double 0.000000e+00
+  %mul166.i = fmul fast double 0.000000e+00, %0
+  %mul177.i = fmul fast double %mul166.i, 0.000000e+00
+  %add178.i = fadd fast double %mul177.i, 0.000000e+00
+  %mul181.i = fmul fast double 0.000000e+00, %1
+  %mul182.i = fmul fast double %mul181.i, 0.000000e+00
+  %add183.i = fadd fast double %mul182.i, 0.000000e+00
+  br label %if.end209.i
+
+if.end209.i:
+  %drdys.1.i = phi double [ %add183.i, %if.then135.i ], [ 0.000000e+00, %exit ]
+  %dbdxs.1.i = phi double [ %add178.i, %if.then135.i ], [ 0.000000e+00, %exit ]
+  ret void
+}