[DAGCombiner] Improve X div/rem Y fold if single bit element type

Summary: Tests by @spatel, thanks

Reviewers: spatel, RKSimon

Reviewed By: spatel

Subscribers: sdardis, atanasyan, llvm-commits, spatel

Differential Revision: https://reviews.llvm.org/D52668

llvm-svn: 345575

1 files changed, 4 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 906223a624c..64c7dca0f6e 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -3138,11 +3138,12 @@ static SDValue simplifyDivRem(SDNode *N, SelectionDAG &DAG) {
 
   // X / 1 -> X
   // X % 1 -> 0
-  if (N1C && N1C->isOne())
-    return IsDiv ? N0 : DAG.getConstant(0, DL, VT);
   // If this is a boolean op (single-bit element type), we can't have
   // division-by-zero or remainder-by-zero, so assume the divisor is 1.
-  // Similarly, if we're zero-extending a boolean divisor, then assume it's a 1.
+  // TODO: Similarly, if we're zero-extending a boolean divisor, then assume
+  // it's a 1.
+  if ((N1C && N1C->isOne()) || (VT.getScalarType() == MVT::i1))
+    return IsDiv ? N0 : DAG.getConstant(0, DL, VT);
 
   return SDValue();
 }