[llvm] r224168 - ValueTracking: Don't recurse too deeply in computeKnownBitsFromAssume

[David Majnemer]

Author: majnemer
Date: Fri Dec 12 17:59:29 2014
New Revision: 224168

URL: http://llvm.org/viewvc/llvm-project?rev=224168&view=rev
Log:
ValueTracking: Don't recurse too deeply in computeKnownBitsFromAssume

Respect the MaxDepth recursion limit, doing otherwise will trigger an
assert in computeKnownBits.

This fixes PR21891.

Added:
    llvm/trunk/test/Transforms/InstCombine/pr21891.ll
Modified:
    llvm/trunk/lib/Analysis/ValueTracking.cpp

Modified: llvm/trunk/lib/Analysis/ValueTracking.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ValueTracking.cpp?rev=224168&r1=224167&r2=224168&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ValueTracking.cpp (original)
+++ llvm/trunk/lib/Analysis/ValueTracking.cpp Fri Dec 12 17:59:29 2014
@@ -511,6 +511,10 @@ static void computeKnownBitsFromAssume(V
       return;
     }
 
+    // The remaining tests are all recursive, so bail out if we hit the limit.
+    if (Depth == MaxDepth)
+      continue;
+
     Value *A, *B;
     auto m_V = m_CombineOr(m_Specific(V),
                            m_CombineOr(m_PtrToInt(m_Specific(V)),

Added: llvm/trunk/test/Transforms/InstCombine/pr21891.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/pr21891.ll?rev=224168&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/pr21891.ll (added)
+++ llvm/trunk/test/Transforms/InstCombine/pr21891.ll Fri Dec 12 17:59:29 2014
@@ -0,0 +1,18 @@
+; RUN: opt %s -instcombine
+
+define i32 @f(i32 %theNumber) {
+entry:
+  %cmp = icmp sgt i32 %theNumber, -1
+  call void @llvm.assume(i1 %cmp)
+  br i1 true, label %if.then, label %if.end
+
+if.then:                                          ; preds = %entry
+  %shl = shl nuw i32 %theNumber, 1
+  br label %if.end
+
+if.end:                                           ; preds = %if.then, %entry
+  %phi = phi i32 [ %shl, %if.then ], [ undef, %entry ]
+  ret i32 %phi
+}
+
+declare void @llvm.assume(i1)