[PATCH] D42044: X86: Utilize ZeroableElements for canWidenShuffleElements

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon added inline comments.


================
Comment at: lib/Target/X86/X86ISelLowering.cpp:14571
+    for (int i = 0, e = Mask.size(); i != e; ++i)
+      if (Mask[i] != SM_SentinelUndef && Zeroable[i])
+        ZeroableMask[i] = SM_SentinelZero;
----------------
Are there any cases where the zero entry came from V1 that could cause a problem?


================
Comment at: lib/Target/X86/X86ISelLowering.cpp:14595
+               "V2's non-undef elements are used?!");
+        APInt Undefs(NewNumElts, -1);
+        SmallVector<APInt, 32> ZeroVecVals(NewNumElts,
----------------
APInt Undefs = APInt::getAllOnesValue(NewNumElts);


================
Comment at: lib/Target/X86/X86ISelLowering.cpp:14597
+        SmallVector<APInt, 32> ZeroVecVals(NewNumElts,
+                                           APInt(NewEltVT.getSizeInBits(), 0));
+        for (int i = 0; i != NewNumElts; ++i)
----------------
APInt::getNullValue(NewEltVT.getSizeInBits())


================
Comment at: lib/Target/X86/X86ISelLowering.cpp:14600
+          if (WidenedMask[i] == SM_SentinelZero) {
+            WidenedMask[i] = i > NewNumElts ? i : i + NewNumElts;
+            Undefs.clearBit(i);
----------------
i > NewNumElts can't ever be true? And anyway, we expect the zero to have come from V2.


Repository:
  rL LLVM

https://reviews.llvm.org/D42044