address more comments

Author: AlexMaclean

llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp

@@ -574,12 +574,17 @@ static Value *foldSelectICmpMinMax(const ICmpInst *Cmp, Value *TVal,
                                    const SimplifyQuery &SQ) {
   const Value *CmpLHS = Cmp->getOperand(0);
   const Value *CmpRHS = Cmp->getOperand(1);
-  const ICmpInst::Predicate Pred = Cmp->getPredicate();
+  ICmpInst::Predicate Pred = Cmp->getPredicate();
 
   // (X > Y) ? X : (Y - 1) ==> MIN(X, Y - 1)
   // (X < Y) ? X : (Y + 1) ==> MAX(X, Y + 1)
   // This transformation is valid when overflow corresponding to the sign of
   // the comparison is poison and we must drop the non-matching overflow flag.
+  if (CmpRHS == TVal) {
+    std::swap(CmpLHS, CmpRHS);
+    Pred = CmpInst::getSwappedPredicate(Pred);
+  }
+
   if (CmpLHS == TVal) {
     if (Pred == CmpInst::ICMP_SGT &&
         match(FVal, m_NSWAddLike(m_Specific(CmpRHS), m_One()))) {

llvm/test/Transforms/InstCombine/minmax-fold.ll

@@ -1647,6 +1647,54 @@ define i32 @test_umin_sub1_nuw(i32 %x, i32 range(i32 1, 0) %w) {
   ret i32 %r
 }
 
+define i32 @test_smin_sub1_nsw_swapped(i32 %x, i32 %w) {
+; CHECK-LABEL: @test_smin_sub1_nsw_swapped(
+; CHECK-NEXT:    [[SUB:%.*]] = add nsw i32 [[W:%.*]], -1
+; CHECK-NEXT:    [[R:%.*]] = call i32 @llvm.smin.i32(i32 [[X:%.*]], i32 [[SUB]])
+; CHECK-NEXT:    ret i32 [[R]]
+;
+  %cmp = icmp sgt i32 %w, %x
+  %sub = add nsw i32 %w, -1
+  %r = select i1 %cmp, i32 %x, i32 %sub
+  ret i32 %r
+}
+
+define i32 @test_smax_add1_nsw_swapped(i32 %x, i32 %w) {
+; CHECK-LABEL: @test_smax_add1_nsw_swapped(
+; CHECK-NEXT:    [[X2:%.*]] = add nsw i32 [[W:%.*]], 1
+; CHECK-NEXT:    [[R:%.*]] = call i32 @llvm.smax.i32(i32 [[X:%.*]], i32 [[X2]])
+; CHECK-NEXT:    ret i32 [[R]]
+;
+  %cmp = icmp slt i32 %w, %x
+  %add = add nsw i32 %w, 1
+  %r = select i1 %cmp, i32 %x, i32 %add
+  ret i32 %r
+}
+
+define i32 @test_umax_add1_nuw_swapped(i32 %x, i32 %w) {
+; CHECK-LABEL: @test_umax_add1_nuw_swapped(
+; CHECK-NEXT:    [[ADD:%.*]] = add nuw i32 [[W:%.*]], 1
+; CHECK-NEXT:    [[R:%.*]] = call i32 @llvm.umax.i32(i32 [[X:%.*]], i32 [[ADD]])
+; CHECK-NEXT:    ret i32 [[R]]
+;
+  %cmp = icmp ult i32 %w, %x
+  %add = add nuw i32 %w, 1
+  %r = select i1 %cmp, i32 %x, i32 %add
+  ret i32 %r
+}
+
+define i32 @test_umin_sub1_nuw_swapped(i32 %x, i32 range(i32 1, 0) %w) {
+; CHECK-LABEL: @test_umin_sub1_nuw_swapped(
+; CHECK-NEXT:    [[SUB:%.*]] = add i32 [[W:%.*]], -1
+; CHECK-NEXT:    [[R:%.*]] = call i32 @llvm.umin.i32(i32 [[X:%.*]], i32 [[SUB]])
+; CHECK-NEXT:    ret i32 [[R]]
+;
+  %cmp = icmp ugt i32 %w, %x
+  %sub = add i32 %w, -1
+  %r = select i1 %cmp, i32 %x, i32 %sub
+  ret i32 %r
+}
+
 define <2 x i16> @test_smin_sub1_nsw_vec(<2 x i16> %x, <2 x i16> %w) {
 ; CHECK-LABEL: @test_smin_sub1_nsw_vec(
 ; CHECK-NEXT:    [[SUB:%.*]] = add nsw <2 x i16> [[W:%.*]], splat (i16 -1)