[llvm] r339515 - [InstSimplify] Guard against large shift amounts.

[Benjamin Kramer via llvm-commits]

Author: d0k
Date: Sun Aug 12 04:43:03 2018
New Revision: 339515

URL: http://llvm.org/viewvc/llvm-project?rev=339515&view=rev
Log:
[InstSimplify] Guard against large shift amounts.

These are always UB, but can happen for large integer inputs. Testing it
is very fragile as -simplifycfg will nuke the UB top-down.

Modified:
    llvm/trunk/lib/Analysis/InstructionSimplify.cpp

Modified: llvm/trunk/lib/Analysis/InstructionSimplify.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/InstructionSimplify.cpp?rev=339515&r1=339514&r2=339515&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/InstructionSimplify.cpp (original)
+++ llvm/trunk/lib/Analysis/InstructionSimplify.cpp Sun Aug 12 04:43:03 2018
@@ -1338,7 +1338,7 @@ static Value *SimplifyLShrInst(Value *Op
     const KnownBits YKnown = computeKnownBits(Y, Q.DL, 0, Q.AC, Q.CxtI, Q.DT);
     const unsigned Width = Op0->getType()->getScalarSizeInBits();
     const unsigned EffWidthY = Width - YKnown.countMinLeadingZeros();
-    if (EffWidthY <= ShRAmt->getZExtValue())
+    if (ShRAmt->uge(EffWidthY))
       return X;
   }
 
@@ -1880,9 +1880,9 @@ static Value *SimplifyAndInst(Value *Op0
       match(Op0, m_c_Or(m_CombineAnd(m_NUWShl(m_Value(X), m_APInt(ShAmt)),
                                      m_Value(XShifted)),
                         m_Value(Y)))) {
-    const unsigned ShftCnt = ShAmt->getZExtValue();
-    const KnownBits YKnown = computeKnownBits(Y, Q.DL, 0, Q.AC, Q.CxtI, Q.DT);
     const unsigned Width = Op0->getType()->getScalarSizeInBits();
+    const unsigned ShftCnt = ShAmt->getLimitedValue(Width);
+    const KnownBits YKnown = computeKnownBits(Y, Q.DL, 0, Q.AC, Q.CxtI, Q.DT);
     const unsigned EffWidthY = Width - YKnown.countMinLeadingZeros();
     if (EffWidthY <= ShftCnt) {
       const KnownBits XKnown = computeKnownBits(X, Q.DL, 0, Q.AC, Q.CxtI,