[SelectionDAG] Don't inspect !range metadata for extended loads

Summary:
Don't call `computeKnownBitsFromRangeMetadata` for extended loads --
this can cause a mismatch between the width of the !range metadata and
the width of the APInt's accumulating `KnownZero` (and `KnownOne` in the
future).  This isn't a problem now, but will be after a future change.

Note: this can be made more aggressive in the future.

Reviewers: nlewycky

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D14107

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@251486 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/SelectionDAG/SelectionDAG.cpp

@@ -2284,7 +2284,8 @@ void SelectionDAG::computeKnownBits(SDValue Op, APInt &KnownZero,
       unsigned MemBits = VT.getScalarType().getSizeInBits();
       KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - MemBits);
     } else if (const MDNode *Ranges = LD->getRanges()) {
-      computeKnownBitsFromRangeMetadata(*Ranges, KnownZero);
+      if (LD->getExtensionType() == ISD::NON_EXTLOAD)
+        computeKnownBitsFromRangeMetadata(*Ranges, KnownZero);
     }
     break;
   }

test/CodeGen/PowerPC/selectiondag-extload-computeknownbits.ll

@@ -0,0 +1,12 @@
+; RUN: llc -mtriple=powerpc64-bgq-linux < %s
+
+; Check that llc does not crash due to an illegal APInt operation
+
+define i1 @f(i8* %ptr) {
+ entry:
+  %val = load i8, i8* %ptr, align 8, !range !0
+  %tobool = icmp eq i8 %val, 0
+  ret i1 %tobool
+}
+
+!0 = !{i8 0, i8 2}