This test case:

long test(long x) { return (x & 123124) | 3; }

Currently compiles to:

_test:
        orl     $3, %edi
        movq    %rdi, %rax
        andq    $123127, %rax
        ret

This is because instruction and DAG combiners canonicalize

  (or (and x, C), D) -> (and (or, D), (C | D))

However, this is only profitable if (C & D) != 0. It gets in the way of the
3-addressification because the input bits are known to be zero.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@97616 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 4 insertions, 2 deletions

diff --git a/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index 8ddaa16ee0..86673f8096 100644
--- a/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -1464,8 +1464,7 @@ Instruction *InstCombiner::visitOr(BinaryOperator &I) {
 
   if (Value *V = SimplifyOrInst(Op0, Op1, TD))
     return ReplaceInstUsesWith(I, V);
-  
-  
+
   // See if we can simplify any instructions used by the instruction whose sole 
   // purpose is to compute bits we don't care about.
   if (SimplifyDemandedInstructionBits(I))
@@ -1474,7 +1473,9 @@ Instruction *InstCombiner::visitOr(BinaryOperator &I) {
   if (ConstantInt *RHS = dyn_cast<ConstantInt>(Op1)) {
     ConstantInt *C1 = 0; Value *X = 0;
     // (X & C1) | C2 --> (X | C2) & (C1|C2)
+    // iff (C1 & C2) == 0.
     if (match(Op0, m_And(m_Value(X), m_ConstantInt(C1))) &&
+        (RHS->getValue() & C1->getValue()) != 0 &&
         Op0->hasOneUse()) {
       Value *Or = Builder->CreateOr(X, RHS);
       Or->takeName(Op0);
@@ -1497,6 +1498,7 @@ Instruction *InstCombiner::visitOr(BinaryOperator &I) {
     if (SelectInst *SI = dyn_cast<SelectInst>(Op0))
       if (Instruction *R = FoldOpIntoSelect(I, SI))
         return R;
+
     if (isa<PHINode>(Op0))
       if (Instruction *NV = FoldOpIntoPhi(I))
         return NV;