Revert r333226 "[ValueTracking] Teach computeKnownBits that the result of an absolute value pattern that uses nsw flag is always positive."

This breaks some libFuzzer tests. http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux-fuzzer/builds/15589/steps/check-fuzzer/logs/stdio

Reverting to investigate

llvm-svn: 333253

1 files changed, 0 insertions, 6 deletions

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 5f5d1be9baa..7f33c67b8ab 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -1078,12 +1078,6 @@ static void computeKnownBitsFromOperator(const Operator *I, KnownBits &Known,
       // leading zero bits.
       MaxHighZeros =
           std::max(Known.countMinLeadingZeros(), Known2.countMinLeadingZeros());
-    } else if (SPF == SPF_ABS) {
-      // RHS from matchSelectPattern returns the negation part of abs pattern.
-      // If the negate has an NSW flag we can assume the sign bit of the result
-      // will be 0 because that makes abs(INT_MIN) undefined.
-      if (cast<Instruction>(RHS)->hasNoSignedWrap())
-        MaxHighZeros = 1;
     }
 
     // Only known if known in both the LHS and RHS.