InstCombine: creating selects from -1 and 0 is fine, they combine into a sext from i1.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122453 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 18 insertions, 3 deletions

diff --git a/lib/Transforms/InstCombine/InstCombineSelect.cpp b/lib/Transforms/InstCombine/InstCombineSelect.cpp
index 82ce31128c..c15378bc74 100644
--- a/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -195,7 +195,10 @@ static bool isSelect01(Constant *C1, Constant *C2) {
   ConstantInt *C2I = dyn_cast<ConstantInt>(C2);
   if (!C2I)
     return false;
-  return (C1I->isZero() || C1I->isOne()) && (C2I->isZero() || C2I->isOne());
+  if (!C1I->isZero() && !C2I->isZero()) // One side must be zero.
+    return false;
+  return C1I->isOne() || C1I->isAllOnesValue() ||
+         C2I->isOne() || C2I->isAllOnesValue();
 }
 
 /// FoldSelectIntoOp - Try fold the select into one of the operands to
@@ -219,7 +222,7 @@ Instruction *InstCombiner::FoldSelectIntoOp(SelectInst &SI, Value *TrueVal,
           Constant *C = GetSelectFoldableConstant(TVI);
           Value *OOp = TVI->getOperand(2-OpToFold);
           // Avoid creating select between 2 constants unless it's selecting
-          // between 0 and 1.
+          // between 0, 1 and -1.
           if (!isa<Constant>(OOp) || isSelect01(C, cast<Constant>(OOp))) {
             Instruction *NewSel = SelectInst::Create(SI.getCondition(), OOp, C);
             InsertNewInstBefore(NewSel, SI);
@@ -248,7 +251,7 @@ Instruction *InstCombiner::FoldSelectIntoOp(SelectInst &SI, Value *TrueVal,
           Constant *C = GetSelectFoldableConstant(FVI);
           Value *OOp = FVI->getOperand(2-OpToFold);
           // Avoid creating select between 2 constants unless it's selecting
-          // between 0 and 1.
+          // between 0, 1 and -1.
           if (!isa<Constant>(OOp) || isSelect01(C, cast<Constant>(OOp))) {
             Instruction *NewSel = SelectInst::Create(SI.getCondition(), C, OOp);
             InsertNewInstBefore(NewSel, SI);
diff --git a/test/Transforms/InstCombine/select.ll b/test/Transforms/InstCombine/select.ll
index 772299c29f..fd3937d3da 100644
--- a/test/Transforms/InstCombine/select.ll
+++ b/test/Transforms/InstCombine/select.ll
@@ -584,3 +584,15 @@ define i32 @test41(i1 %cond, i32 %x, i32 %y) {
 ; CHECK-NEXT: and i32 %x, %y
 ; CHECK-NEXT: ret i32
 }
+
+define i32 @test42(i32 %x, i32 %y) {
+  %b = add i32 %y, -1
+  %cond = icmp eq i32 %x, 0
+  %c = select i1 %cond, i32 %b, i32 %y
+  ret i32 %c
+; CHECK: @test42
+; CHECK-NEXT: %cond = icmp eq i32 %x, 0
+; CHECK-NEXT: %b = sext i1 %cond to i32
+; CHECK-NEXT: %c = add i32 %b, %y
+; CHECK-NEXT: ret i32 %c
+}