[InstCombine] Shift amount reassociation in bittest: relax one-use check when shifting constant

If one of the values being shifted is a constant, since the new shift
amount is known-constant, the new shift will end up being constant-folded
so, we don't need that one-use restriction then.

llvm-svn: 368519

1 files changed, 11 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index edad6a45121..f82a5b1806c 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -3314,7 +3314,7 @@ foldShiftIntoShiftInAnotherHandOfAndInICmp(ICmpInst &I, const SimplifyQuery SQ,
   // Pick the single-use shift as XShift.
   Value *XShift, *YShift;
   if (!match(I.getOperand(0),
-             m_c_And(m_OneUse(m_CombineAnd(m_AnyLogicalShift, m_Value(XShift))),
+             m_c_And(m_CombineAnd(m_AnyLogicalShift, m_Value(XShift)),
                      m_CombineAnd(m_AnyLogicalShift, m_Value(YShift)))))
     return nullptr;
 
@@ -3332,6 +3332,16 @@ foldShiftIntoShiftInAnotherHandOfAndInICmp(ICmpInst &I, const SimplifyQuery SQ,
   match(XShift, m_BinOp(m_Value(X), m_Value(XShAmt)));
   match(YShift, m_BinOp(m_Value(Y), m_Value(YShAmt)));
 
+  // If one of the values being shifted is a constant, then we will end with
+  // and+icmp, and shift instr will be constant-folded. If they are not,
+  // however, we will need to ensure that we won't increase instruction count.
+  if (!isa<Constant>(X) && !isa<Constant>(Y)) {
+    // At least one of the hands of the 'and' should be one-use shift.
+    if (!match(I.getOperand(0),
+               m_c_And(m_OneUse(m_AnyLogicalShift), m_Value())))
+      return nullptr;
+  }
+
   // Can we fold (XShAmt+YShAmt) ?
   Value *NewShAmt = SimplifyBinOp(Instruction::BinaryOps::Add, XShAmt, YShAmt,
                                   SQ.getWithInstruction(&I));