Merging r323331:

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r323331 | spatel | 2018-01-24 16:20:37 +0100 (Wed, 24 Jan 2018) | 21 lines

[ValueTracking] add recursion depth param to matchSelectPattern 

We're getting bug reports:
https://bugs.llvm.org/show_bug.cgi?id=35807
https://bugs.llvm.org/show_bug.cgi?id=35840
https://bugs.llvm.org/show_bug.cgi?id=36045
...where we blow up the stack in value tracking because other passes are sending 
in selects that have an operand that is itself the select.

We don't currently have a reliable way to avoid analyzing dead code that may take 
non-standard forms, so bail out when things go too far.

This mimics the recursion depth limitations in other parts of value tracking.

Unfortunately, this pushes the underlying problems for other passes (jump-threading,
simplifycfg, correlated-propagation) into hiding. If someone wants to uncover those
again, the first draft of this patch on Phab would do that (it would assert rather
than bail out).

Differential Revision: https://reviews.llvm.org/D42442

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_60@323737 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 46 insertions, 0 deletions

diff --git a/test/Analysis/ValueTracking/select-pattern.ll b/test/Analysis/ValueTracking/select-pattern.ll
new file mode 100644
index 00000000000..455df00ef12
--- /dev/null
+++ b/test/Analysis/ValueTracking/select-pattern.ll
@@ -0,0 +1,46 @@
+; RUN: opt -simplifycfg < %s -S | FileCheck %s
+
+; The dead code would cause a select that had itself
+; as an operand to be analyzed. This would then cause
+; infinite recursion and eventual crash.
+
+define void @PR36045(i1 %t, i32* %b) {
+; CHECK-LABEL: @PR36045(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    ret void
+;
+entry:
+  br i1 %t, label %if, label %end
+
+if:
+  br i1 %t, label %unreach, label %pre
+
+unreach:
+  unreachable
+
+pre:
+  %p = phi i32 [ 70, %if ], [ %sel, %for ]
+  br label %for
+
+for:
+  %cmp = icmp sgt i32 %p, 8
+  %add = add i32 %p, 2
+  %sel = select i1 %cmp, i32 %p, i32 %add
+  %cmp21 = icmp ult i32 %sel, 21
+  br i1 %cmp21, label %pre, label %for.end
+
+for.end:
+  br i1 %t, label %unreach2, label %then12
+
+then12:
+  store i32 0, i32* %b
+  br label %unreach2
+
+unreach2:
+  %spec = phi i32 [ %sel, %for.end ], [ 42, %then12 ]
+  unreachable
+
+end:
+  ret void
+}
+