[PatternMatch, InstSimplify] enhance m_AllOnes() to ignore undef elements in vectors

Loosening the matcher definition reveals a subtle bug in InstSimplify (we should not
assume that because an operand constant matches that it's safe to return it as a result).

So I'm making that change here too (that diff could be independent, but I'm not sure how 
to reveal it before the matcher change).

This also seems like a good reason to *not* include matchers that capture the value.
We don't want to encourage the potential misstep of propagating undef values when it's
not allowed/intended.

I didn't include the capture variant option here or in the related rL325437 (m_One), 
but it already exists for other constant matchers.

llvm-svn: 325466

1 files changed, 7 insertions, 11 deletions

diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index 34a10c5d5ea..a424e693842 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -1264,9 +1264,10 @@ static Value *SimplifyAShrInst(Value *Op0, Value *Op1, bool isExact,
                                     MaxRecurse))
     return V;
 
-  // all ones >>a X -> all ones
+  // all ones >>a X -> -1
+  // Do not return Op0 because it may contain undef elements if it's a vector.
   if (match(Op0, m_AllOnes()))
-    return Op0;
+    return Constant::getAllOnesValue(Op0->getType());
 
   // (X << A) >> A -> X
   Value *X;
@@ -1783,21 +1784,16 @@ static Value *SimplifyOrInst(Value *Op0, Value *Op1, const SimplifyQuery &Q,
     return C;
 
   // X | undef -> -1
-  if (match(Op1, m_Undef()))
+  // X | -1 = -1
+  // Do not return Op1 because it may contain undef elements if it's a vector.
+  if (match(Op1, m_Undef()) || match(Op1, m_AllOnes()))
     return Constant::getAllOnesValue(Op0->getType());
 
   // X | X = X
-  if (Op0 == Op1)
-    return Op0;
-
   // X | 0 = X
-  if (match(Op1, m_Zero()))
+  if (Op0 == Op1 || match(Op1, m_Zero()))
     return Op0;
 
-  // X | -1 = -1
-  if (match(Op1, m_AllOnes()))
-    return Op1;
-
   // A | ~A  =  ~A | A  =  -1
   if (match(Op0, m_Not(m_Specific(Op1))) ||
       match(Op1, m_Not(m_Specific(Op0))))