Fix DAGCombiner to avoid going into an infinite loop when it

encounters (and:i64 (shl:i64 (load:i64), 1), 0xffffffff).
This fixes rdar://8606584.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@118143 91177308-0d34-0410-b5e6-96231b3b80d8

test/CodeGen/X86/narrow-shl-load.ll

@@ -0,0 +1,32 @@
+; RUN: llc -march=x86-64 < %s
+
+; DAGCombiner should fold this code in finite time.
+
+; rdar://8606584
+
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
+target triple = "x86_64-pc-linux-gnu"
+
+define void @D() nounwind readnone {
+bb.nph:
+  br label %while.cond
+
+while.cond:                                       ; preds = %while.cond, %bb.nph
+  %tmp6 = load i32* undef, align 4
+  %and = or i64 undef, undef
+  %conv11 = zext i32 undef to i64
+  %conv14 = zext i32 %tmp6 to i64
+  %shl15 = shl i64 %conv14, 1
+  %shl15.masked = and i64 %shl15, 4294967294
+  %and17 = or i64 %shl15.masked, %conv11
+  %add = add i64 %and17, 1
+  %xor = xor i64 %add, %and
+  %tmp20 = load i64* undef, align 8
+  %add21 = add i64 %xor, %tmp20
+  %conv22 = trunc i64 %add21 to i32
+  store i32 %conv22, i32* undef, align 4
+  br i1 false, label %while.end, label %while.cond
+
+while.end:                                        ; preds = %while.cond
+  ret void
+}