From 77e22b7836613f97bfd7579e064b66e3ebc6c2f3 Mon Sep 17 00:00:00 2001
From: David Majnemer <david.majnemer@gmail.com>
Date: Sun, 4 Jan 2015 07:06:53 +0000
Subject: [PATCH] ValueTracking: ComputeNumSignBits should tolerate misshapen
 phi nodes

PHI nodes can have zero operands in the middle of a transform.  It is
expected that utilities in Analysis don't freak out when this happens.

Note that it is considered invalid to allow these misshapen phi nodes to
make it to another pass.

This fixes PR22086.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@225126 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Analysis/ValueTracking.cpp           |  7 ++++--
 test/Transforms/JumpThreading/pr22086.ll | 28 ++++++++++++++++++++++++
 2 files changed, 33 insertions(+), 2 deletions(-)
 create mode 100644 test/Transforms/JumpThreading/pr22086.ll

diff --git a/lib/Analysis/ValueTracking.cpp b/lib/Analysis/ValueTracking.cpp
index 6fdf4afebc2..b292af6cee7 100644
--- a/lib/Analysis/ValueTracking.cpp
+++ b/lib/Analysis/ValueTracking.cpp
@@ -1821,13 +1821,16 @@ unsigned ComputeNumSignBits(Value *V, const DataLayout *TD,
 
   case Instruction::PHI: {
     PHINode *PN = cast<PHINode>(U);
+    unsigned NumIncomingValues = PN->getNumIncomingValues();
     // Don't analyze large in-degree PHIs.
-    if (PN->getNumIncomingValues() > 4) break;
+    if (NumIncomingValues > 4) break;
+    // Unreachable blocks may have zero-operand PHI nodes.
+    if (NumIncomingValues == 0) break;
 
     // Take the minimum of all incoming values.  This can't infinitely loop
     // because of our depth threshold.
     Tmp = ComputeNumSignBits(PN->getIncomingValue(0), TD, Depth+1, Q);
-    for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i) {
+    for (unsigned i = 1, e = NumIncomingValues; i != e; ++i) {
       if (Tmp == 1) return Tmp;
       Tmp = std::min(Tmp,
                      ComputeNumSignBits(PN->getIncomingValue(i), TD,
diff --git a/test/Transforms/JumpThreading/pr22086.ll b/test/Transforms/JumpThreading/pr22086.ll
new file mode 100644
index 00000000000..35d9aa5b184
--- /dev/null
+++ b/test/Transforms/JumpThreading/pr22086.ll
@@ -0,0 +1,28 @@
+; RUN: opt -S -jump-threading < %s | FileCheck %s
+
+
+; CHECK-LABEL: @f(
+; CHECK-LABEL: entry:
+; CHECK-NEXT:  br label %[[loop:.*]]
+; CHECK:       [[loop]]:
+; CHECK-NEXT:  br label %[[loop]]
+
+define void @f() {
+entry:
+  br label %for.cond1
+
+if.end16:
+  %phi1 = phi i32 [ undef, %for.cond1 ]
+  %g.3 = phi i32 [ %g.1, %for.cond1 ]
+  %sext = shl i32 %g.3, 16
+  %conv20 = ashr exact i32 %sext, 16
+  %tobool21 = icmp eq i32 %phi1, 0
+  br i1 %tobool21, label %lor.rhs, label %for.cond1
+
+for.cond1:
+  %g.1 = phi i32 [ 0, %entry ], [ 0, %lor.rhs ], [ %g.3, %if.end16 ]
+  br i1 undef, label %lor.rhs, label %if.end16
+
+lor.rhs:
+  br label %for.cond1
+}
-- 
2.34.1