diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
--- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1529,6 +1529,31 @@
   return Builder.CreateIntCast(Result, Ty, true);
 }
 
+/// If we have:
+///   x - ((x / y) * y)
+/// We can transform it into:
+///   x % y
+static Instruction *
+produceRemFromSubtractionOfRoundeddownValue(BinaryOperator &I) {
+  assert(I.getOpcode() == Instruction::Sub && "Must start from 'sub'.");
+
+  Value *X = I.getOperand(0);
+  Value *XroundedDownToMultipleOfY = I.getOperand(1);
+
+  Value *Y;
+  Instruction *Div;
+  // Look for  ((x / y) * y)
+  if (!match(XroundedDownToMultipleOfY,
+             m_c_Mul(m_CombineAnd(m_IDiv(m_Specific(X), m_Value(Y)),
+                                  m_Instruction(Div)),
+                     m_Deferred(Y))))
+    return nullptr;
+
+  return Div->getOpcode() == Instruction::SDiv
+             ? BinaryOperator::CreateSRem(X, Y, I.getName())
+             : BinaryOperator::CreateURem(X, Y, I.getName());
+}
+
 Instruction *InstCombiner::visitSub(BinaryOperator &I) {
   if (Value *V = SimplifySubInst(I.getOperand(0), I.getOperand(1),
                                  I.hasNoSignedWrap(), I.hasNoUnsignedWrap(),
@@ -1791,6 +1816,9 @@
     }
   }
 
+  if (Instruction *Ext = produceRemFromSubtractionOfRoundeddownValue(I))
+    return Ext;
+
   // Optimize pointer differences into the same array into a size.  Consider:
   //  &A[10] - &A[0]: we should compile this to "10".
   Value *LHSOp, *RHSOp;
diff --git a/llvm/test/Transforms/InstCombine/srem-via-sdiv-mul-sub.ll b/llvm/test/Transforms/InstCombine/srem-via-sdiv-mul-sub.ll
--- a/llvm/test/Transforms/InstCombine/srem-via-sdiv-mul-sub.ll
+++ b/llvm/test/Transforms/InstCombine/srem-via-sdiv-mul-sub.ll
@@ -18,8 +18,7 @@
 ; CHECK-LABEL: @t0_basic(
 ; CHECK-NEXT:    [[DIV:%.*]] = sdiv i8 [[X:%.*]], [[Y:%.*]]
 ; CHECK-NEXT:    call void @use8(i8 [[DIV]])
-; CHECK-NEXT:    [[ROUNDXDOWNTOMULTIPLEOFY:%.*]] = mul i8 [[DIV]], [[Y]]
-; CHECK-NEXT:    [[REM:%.*]] = sub i8 [[X]], [[ROUNDXDOWNTOMULTIPLEOFY]]
+; CHECK-NEXT:    [[REM:%.*]] = srem i8 [[X]], [[Y]]
 ; CHECK-NEXT:    ret i8 [[REM]]
 ;
   %div = sdiv i8 %x, %y
@@ -33,8 +32,7 @@
 ; CHECK-LABEL: @t1_vector(
 ; CHECK-NEXT:    [[DIV:%.*]] = sdiv <2 x i8> [[X:%.*]], [[Y:%.*]]
 ; CHECK-NEXT:    call void @use2xi8(<2 x i8> [[DIV]])
-; CHECK-NEXT:    [[ROUNDXDOWNTOMULTIPLEOFY:%.*]] = mul <2 x i8> [[DIV]], [[Y]]
-; CHECK-NEXT:    [[REM:%.*]] = sub <2 x i8> [[X]], [[ROUNDXDOWNTOMULTIPLEOFY]]
+; CHECK-NEXT:    [[REM:%.*]] = srem <2 x i8> [[X]], [[Y]]
 ; CHECK-NEXT:    ret <2 x i8> [[REM]]
 ;
   %div = sdiv <2 x i8> %x, %y
@@ -52,7 +50,7 @@
 ; CHECK-NEXT:    call void @use8(i8 [[DIV]])
 ; CHECK-NEXT:    [[ROUNDXDOWNTOMULTIPLEOFY:%.*]] = mul i8 [[DIV]], [[Y]]
 ; CHECK-NEXT:    call void @use8(i8 [[ROUNDXDOWNTOMULTIPLEOFY]])
-; CHECK-NEXT:    [[REM:%.*]] = sub i8 [[X]], [[ROUNDXDOWNTOMULTIPLEOFY]]
+; CHECK-NEXT:    [[REM:%.*]] = srem i8 [[X]], [[Y]]
 ; CHECK-NEXT:    ret i8 [[REM]]
 ;
   %div = sdiv i8 %x, %y
@@ -72,8 +70,7 @@
 ; CHECK-NEXT:    [[Y:%.*]] = call i8 @gen8()
 ; CHECK-NEXT:    [[DIV:%.*]] = sdiv i8 [[X:%.*]], [[Y]]
 ; CHECK-NEXT:    call void @use8(i8 [[DIV]])
-; CHECK-NEXT:    [[ROUNDXDOWNTOMULTIPLEOFY:%.*]] = mul i8 [[Y]], [[DIV]]
-; CHECK-NEXT:    [[REM:%.*]] = sub i8 [[X]], [[ROUNDXDOWNTOMULTIPLEOFY]]
+; CHECK-NEXT:    [[REM:%.*]] = srem i8 [[X]], [[Y]]
 ; CHECK-NEXT:    ret i8 [[REM]]
 ;
   %y = call i8 @gen8()
diff --git a/llvm/test/Transforms/InstCombine/urem-via-udiv-mul-sub.ll b/llvm/test/Transforms/InstCombine/urem-via-udiv-mul-sub.ll
--- a/llvm/test/Transforms/InstCombine/urem-via-udiv-mul-sub.ll
+++ b/llvm/test/Transforms/InstCombine/urem-via-udiv-mul-sub.ll
@@ -18,8 +18,7 @@
 ; CHECK-LABEL: @t0_basic(
 ; CHECK-NEXT:    [[DIV:%.*]] = udiv i8 [[X:%.*]], [[Y:%.*]]
 ; CHECK-NEXT:    call void @use8(i8 [[DIV]])
-; CHECK-NEXT:    [[ROUNDXDOWNTOMULTIPLEOFY:%.*]] = mul i8 [[DIV]], [[Y]]
-; CHECK-NEXT:    [[REM:%.*]] = sub i8 [[X]], [[ROUNDXDOWNTOMULTIPLEOFY]]
+; CHECK-NEXT:    [[REM:%.*]] = urem i8 [[X]], [[Y]]
 ; CHECK-NEXT:    ret i8 [[REM]]
 ;
   %div = udiv i8 %x, %y
@@ -33,8 +32,7 @@
 ; CHECK-LABEL: @t1_vector(
 ; CHECK-NEXT:    [[DIV:%.*]] = udiv <2 x i8> [[X:%.*]], [[Y:%.*]]
 ; CHECK-NEXT:    call void @use2xi8(<2 x i8> [[DIV]])
-; CHECK-NEXT:    [[ROUNDXDOWNTOMULTIPLEOFY:%.*]] = mul <2 x i8> [[DIV]], [[Y]]
-; CHECK-NEXT:    [[REM:%.*]] = sub <2 x i8> [[X]], [[ROUNDXDOWNTOMULTIPLEOFY]]
+; CHECK-NEXT:    [[REM:%.*]] = urem <2 x i8> [[X]], [[Y]]
 ; CHECK-NEXT:    ret <2 x i8> [[REM]]
 ;
   %div = udiv <2 x i8> %x, %y
@@ -52,7 +50,7 @@
 ; CHECK-NEXT:    call void @use8(i8 [[DIV]])
 ; CHECK-NEXT:    [[ROUNDXDOWNTOMULTIPLEOFY:%.*]] = mul i8 [[DIV]], [[Y]]
 ; CHECK-NEXT:    call void @use8(i8 [[ROUNDXDOWNTOMULTIPLEOFY]])
-; CHECK-NEXT:    [[REM:%.*]] = sub i8 [[X]], [[ROUNDXDOWNTOMULTIPLEOFY]]
+; CHECK-NEXT:    [[REM:%.*]] = urem i8 [[X]], [[Y]]
 ; CHECK-NEXT:    ret i8 [[REM]]
 ;
   %div = udiv i8 %x, %y
@@ -72,8 +70,7 @@
 ; CHECK-NEXT:    [[Y:%.*]] = call i8 @gen8()
 ; CHECK-NEXT:    [[DIV:%.*]] = udiv i8 [[X:%.*]], [[Y]]
 ; CHECK-NEXT:    call void @use8(i8 [[DIV]])
-; CHECK-NEXT:    [[ROUNDXDOWNTOMULTIPLEOFY:%.*]] = mul i8 [[Y]], [[DIV]]
-; CHECK-NEXT:    [[REM:%.*]] = sub i8 [[X]], [[ROUNDXDOWNTOMULTIPLEOFY]]
+; CHECK-NEXT:    [[REM:%.*]] = urem i8 [[X]], [[Y]]
 ; CHECK-NEXT:    ret i8 [[REM]]
 ;
   %y = call i8 @gen8()