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

diff --git a/lib/Analysis/ValueTracking.cpp b/lib/Analysis/ValueTracking.cpp
index 6fdf4afebc2bf97f0958d837f5daf17433cb45cc..b292af6cee77fc9cf70891f0b244bbf686feb0cc 100644 (file)
--- 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 (file)
index 0000000..35d9aa5
--- /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
+}