[x86] Fix compile fail in combineX86ShufflesRecursively function in case of IncomingMask has -1 elements

[rob.khasanov]

Summary

Fix compile fail in combineX86ShufflesRecursively function in case of IncomingMask has -1 elements.
If IncomingMask[i] = -1 for some i, push -1 to Mask instead of OpMask[IncomingMask[i]]
PR20540

[chandlerc]

Obsolete after a deeper fix was applied.

lib/Target/X86/X86ISelLowering.cpp

assert(VT.getVectorNumElements() == OpMask.size() &&
          "Different mask size from vector size!");
 
   SmallVector<int, 16> Mask;
   Mask.reserve(std::max(OpMask.size(), IncomingMask.size()));
 
   // Merge this shuffle operation's mask into our accumulated mask. This is
   // a bit tricky as the shuffle may have a different size from the root.
   if (OpMask.size() == IncomingMask.size()) {
-    for (int M : IncomingMask)
+    for (int M : IncomingMask) {
+      if (M == SM_SentinelZero)
+        Mask.push_back(SM_SentinelZero);
+      else
         Mask.push_back(OpMask[M]);
+    }
   } else if (OpMask.size() < IncomingMask.size()) {
     assert(IncomingMask.size() % OpMask.size() == 0 &&
            "The smaller number of elements must divide the larger.");
     int Ratio = IncomingMask.size() / OpMask.size();
     for (int M : IncomingMask)
       Mask.push_back(Ratio * OpMask[M / Ratio] + M % Ratio);
   } else {
     assert(OpMask.size() > IncomingMask.size() && "All other cases handled!");

test/CodeGen/X86/pr20540.ll

+; RUN: llc  < %s -mtriple=x86_64-apple-darwin -march=x86  -mcpu=corei7 | FileCheck %s
+
+declare i32 @llvm.x86.sse2.pmovmskb.128(<16 x i8>)
+
+define void @f_fu_(float* noalias nocapture %RET, <8 x i8> %__mask) {
+  ; CHECK: pshufb
+  %mask8.i.i.i = shufflevector <8 x i8> %__mask, <8 x i8> zeroinitializer, <16 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 8, i32 8, i32 8, i32 8, i32 8, i32 8, i32 8, i32 8>
+  %m.i.i.i = call i32 @llvm.x86.sse2.pmovmskb.128(<16 x i8> %mask8.i.i.i)
+  %RET.i = bitcast float* %RET to i32*
+  store i32 %m.i.i.i, i32* %RET.i
+  ret void
+}
+