Index: lib/CodeGen/SelectionDAG/DAGCombiner.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -2288,10 +2288,12 @@
   if (SDValue V = foldAddSubMasked1(true, N0, N1, DAG, DL))
     return V;
 
-  // add (sext i1), X -> sub X, (zext i1)
+  // If the target's bool is represented as 0/1, prefer to make this 'sub 0/1'
+  // rather than 'add 0/-1' (the zext should get folded).
+  // add (sext i1 Y), X --> sub X, (zext i1 Y)
   if (N0.getOpcode() == ISD::SIGN_EXTEND &&
-      N0.getOperand(0).getValueType() == MVT::i1 &&
-      !TLI.isOperationLegal(ISD::SIGN_EXTEND, MVT::i1)) {
+      N0.getOperand(0).getScalarValueSizeInBits() == 1 &&
+      TLI.getBooleanContents(VT) == TargetLowering::ZeroOrOneBooleanContent) {
     SDValue ZExt = DAG.getNode(ISD::ZERO_EXTEND, DL, VT, N0.getOperand(0));
     return DAG.getNode(ISD::SUB, DL, VT, N1, ZExt);
   }
@@ -2739,6 +2741,17 @@
   if (SDValue V = foldAddSubMasked1(false, N0, N1, DAG, SDLoc(N)))
     return V;
 
+  // If the target's bool is represented as 0/-1, prefer to make this 'add 0/-1'
+  // rather than 'sub 0/1' (the sext should get folded).
+  // sub X, (zext i1 Y) --> add X, (sext i1 Y)
+  if (N1.getOpcode() == ISD::ZERO_EXTEND &&
+      N1.getOperand(0).getScalarValueSizeInBits() == 1 &&
+      TLI.getBooleanContents(VT) ==
+          TargetLowering::ZeroOrNegativeOneBooleanContent) {
+    SDValue SExt = DAG.getNode(ISD::SIGN_EXTEND, DL, VT, N1.getOperand(0));
+    return DAG.getNode(ISD::ADD, DL, VT, N0, SExt);
+  }
+
   // fold Y = sra (X, size(X)-1); sub (xor (X, Y), Y) -> (abs X)
   if (TLI.isOperationLegalOrCustom(ISD::ABS, VT)) {
     if (N0.getOpcode() == ISD::XOR && N1.getOpcode() == ISD::SRA) {
Index: test/CodeGen/PowerPC/bool-math.ll
===================================================================
--- test/CodeGen/PowerPC/bool-math.ll
+++ test/CodeGen/PowerPC/bool-math.ll
@@ -83,9 +83,8 @@
 define i32 @low_bit_select_constants_bigger_false_same_size_result(i32 %x) {
 ; CHECK-LABEL: low_bit_select_constants_bigger_false_same_size_result:
 ; CHECK:       # %bb.0:
-; CHECK-NEXT:    not 3, 3
 ; CHECK-NEXT:    clrldi 3, 3, 63
-; CHECK-NEXT:    subfic 3, 3, 43
+; CHECK-NEXT:    ori 3, 3, 42
 ; CHECK-NEXT:    blr
   %a = and i32 %x, 1
   %c = icmp eq i32 %a, 0
@@ -96,9 +95,8 @@
 define i64 @low_bit_select_constants_bigger_false_wider_result(i32 %x) {
 ; CHECK-LABEL: low_bit_select_constants_bigger_false_wider_result:
 ; CHECK:       # %bb.0:
-; CHECK-NEXT:    not 3, 3
 ; CHECK-NEXT:    clrldi 3, 3, 63
-; CHECK-NEXT:    subfic 3, 3, 27
+; CHECK-NEXT:    ori 3, 3, 26
 ; CHECK-NEXT:    blr
   %a = and i32 %x, 1
   %c = icmp eq i32 %a, 0
@@ -109,9 +107,8 @@
 define i16 @low_bit_select_constants_bigger_false_narrower_result(i32 %x) {
 ; CHECK-LABEL: low_bit_select_constants_bigger_false_narrower_result:
 ; CHECK:       # %bb.0:
-; CHECK-NEXT:    nor 3, 3, 3
-; CHECK-NEXT:    clrlwi 3, 3, 31
-; CHECK-NEXT:    subfic 3, 3, 37
+; CHECK-NEXT:    clrldi 3, 3, 63
+; CHECK-NEXT:    ori 3, 3, 36
 ; CHECK-NEXT:    blr
   %a = and i32 %x, 1
   %c = icmp eq i32 %a, 0
Index: test/CodeGen/PowerPC/signbit-shift.ll
===================================================================
--- test/CodeGen/PowerPC/signbit-shift.ll
+++ test/CodeGen/PowerPC/signbit-shift.ll
@@ -69,9 +69,8 @@
 define i32 @add_sext_ifpos(i32 %x) {
 ; CHECK-LABEL: add_sext_ifpos:
 ; CHECK:       # %bb.0:
-; CHECK-NEXT:    nor 3, 3, 3
-; CHECK-NEXT:    srawi 3, 3, 31
-; CHECK-NEXT:    addi 3, 3, 42
+; CHECK-NEXT:    srwi 3, 3, 31
+; CHECK-NEXT:    addi 3, 3, 41
 ; CHECK-NEXT:    blr
   %c = icmp sgt i32 %x, -1
   %e = sext i1 %c to i32