[LoopUnrollAnalyzer] Bail out instead of dying with assert when facing huge index.

This fixes PR27902.

llvm-svn: 270946

llvm/lib/Analysis/LoopUnrollAnalyzer.cpp

@@ -119,8 +119,8 @@ bool UnrolledInstAnalyzer::visitLoad(LoadInst &I) {
     return false;
 
   int ElemSize = CDS->getElementType()->getPrimitiveSizeInBits() / 8U;
-  assert(SimplifiedAddrOp->getValue().getActiveBits() < 64 &&
-         "Unexpectedly large index value.");
+  if (SimplifiedAddrOp->getValue().getActiveBits() >= 64)
+    return false;
   int64_t Index = SimplifiedAddrOp->getSExtValue() / ElemSize;
   if (Index >= CDS->getNumElements()) {
     // FIXME: For now we conservatively ignore out of bound accesses, but

llvm/test/Transforms/LoopUnroll/full-unroll-crashers.ll

@@ -167,3 +167,24 @@ for.inc:
 for.end:
   ret void
 }
+
+define void @index_too_large() {
+entry:
+  br label %for.body
+
+for.body:
+  %iv = phi i64 [ -73631599, %entry ], [ %iv.next, %for.inc ]
+  br i1 undef, label %for.body2, label %for.inc
+
+for.body2:
+  %idx = getelementptr inbounds [10 x i32], [10 x i32]* @known_constant, i64 0, i64 %iv
+  %x = load i32, i32* %idx, align 1
+  br label %for.inc
+
+for.inc:
+  %iv.next = add nsw i64 %iv, -1
+  br i1 undef, label %for.body, label %for.end
+
+for.end:
+  ret void
+}