diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -2264,6 +2264,36 @@
             Call, Builder.CreateBitOrPointerCast(ReturnedArg, CallTy));
     }
 
+  // Simplify nonnull arguments if possible.
+  //   ptr = select _, null, p
+  //   f(nonnull ptr)
+  // =>
+  //   f(nonnull p)
+  for (unsigned ArgNo = 0, N = Call.getNumArgOperands(); ArgNo != N; ++ArgNo) {
+    if (!Call.paramHasAttr(ArgNo, Attribute::NonNull))
+      continue;
+
+    Value *V = Call.getArgOperand(ArgNo);
+    Value *Cond, *TrueVal, *FalseVal;
+    if (!match(V, m_Select(m_Value(Cond), m_Value(TrueVal), m_Value(FalseVal))))
+      continue;
+
+    bool IsTrueNull = isa<ConstantPointerNull>(TrueVal);
+    if (IsTrueNull || isa<ConstantPointerNull>(FalseVal)) {
+      replaceUse(Call.getArgOperandUse(ArgNo), IsTrueNull ? FalseVal : TrueVal);
+
+      if (Call.paramHasAttr(ArgNo, Attribute::NoUndef)) {
+        //   ptr = select cond, null, p
+        //   f(nonnull noundef ptr)
+        // =>
+        //   llvm.assume(!cond)
+        //   f(nonnull noundef p)
+        Builder.CreateAssumption(IsTrueNull ? Builder.CreateNot(Cond) : Cond);
+      }
+      Changed = true;
+    }
+  }
+
   if (isAllocLikeFn(&Call, &TLI))
     return visitAllocSite(Call);
 
diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -2844,6 +2844,31 @@
     return nullptr;
 
   Value *ResultOp = RI.getOperand(0);
+
+  auto Attrs = RI.getFunction()->getAttributes();
+  if (Attrs.hasAttribute(AttributeList::ReturnIndex, Attribute::NonNull)) {
+    //   ptr = select _, null, p
+    //   ret nonnull ptr
+    // =>
+    //   ret nonnull p
+    Value *Cond, *TrueVal, *FalseVal;
+    if (match(ResultOp,
+              m_Select(m_Value(Cond), m_Value(TrueVal), m_Value(FalseVal))) &&
+        (isa<ConstantPointerNull>(TrueVal) ||
+         isa<ConstantPointerNull>(FalseVal))) {
+      bool IsTrueNull = isa<ConstantPointerNull>(TrueVal);
+      if (Attrs.hasAttribute(AttributeList::ReturnIndex, Attribute::NoUndef)) {
+        //   ptr = select cond, null, p
+        //   ret noundef nonnull ptr
+        // =>
+        //   llvm.assume(!cond)
+        //   ret noundef nonnull p
+        Builder.CreateAssumption(IsTrueNull ? Builder.CreateNot(Cond) : Cond);
+      }
+      return replaceOperand(RI, 0, IsTrueNull ? FalseVal : TrueVal);
+    }
+  }
+
   Type *VTy = ResultOp->getType();
   if (!VTy->isIntegerTy() || isa<Constant>(ResultOp))
     return nullptr;
diff --git a/llvm/test/Transforms/InstCombine/nonnull-select.ll b/llvm/test/Transforms/InstCombine/nonnull-select.ll
--- a/llvm/test/Transforms/InstCombine/nonnull-select.ll
+++ b/llvm/test/Transforms/InstCombine/nonnull-select.ll
@@ -5,11 +5,8 @@
 
 define nonnull i32* @pr48975(i32** %.0) {
 ; CHECK-LABEL: @pr48975(
-; CHECK-NEXT:    [[DOT1:%.*]] = load i32*, i32** [[DOT0:%.*]], align 8
-; CHECK-NEXT:    [[DOT2:%.*]] = icmp eq i32* [[DOT1]], null
-; CHECK-NEXT:    [[DOT3:%.*]] = bitcast i32** [[DOT0]] to i32*
-; CHECK-NEXT:    [[DOT4:%.*]] = select i1 [[DOT2]], i32* null, i32* [[DOT3]]
-; CHECK-NEXT:    ret i32* [[DOT4]]
+; CHECK-NEXT:    [[DOT3:%.*]] = bitcast i32** [[DOT0:%.*]] to i32*
+; CHECK-NEXT:    ret i32* [[DOT3]]
 ;
   %.1 = load i32*, i32** %.0, align 8
   %.2 = icmp eq i32* %.1, null
@@ -20,8 +17,7 @@
 
 define nonnull i32* @nonnull_ret(i1 %cond, i32* %p) {
 ; CHECK-LABEL: @nonnull_ret(
-; CHECK-NEXT:    [[RES:%.*]] = select i1 [[COND:%.*]], i32* [[P:%.*]], i32* null
-; CHECK-NEXT:    ret i32* [[RES]]
+; CHECK-NEXT:    ret i32* [[P:%.*]]
 ;
   %res = select i1 %cond, i32* %p, i32* null
   ret i32* %res
@@ -29,8 +25,7 @@
 
 define nonnull i32* @nonnull_ret2(i1 %cond, i32* %p) {
 ; CHECK-LABEL: @nonnull_ret2(
-; CHECK-NEXT:    [[RES:%.*]] = select i1 [[COND:%.*]], i32* null, i32* [[P:%.*]]
-; CHECK-NEXT:    ret i32* [[RES]]
+; CHECK-NEXT:    ret i32* [[P:%.*]]
 ;
   %res = select i1 %cond, i32* null, i32* %p
   ret i32* %res
@@ -38,8 +33,8 @@
 
 define nonnull noundef i32* @nonnull_noundef_ret(i1 %cond, i32* %p) {
 ; CHECK-LABEL: @nonnull_noundef_ret(
-; CHECK-NEXT:    [[RES:%.*]] = select i1 [[COND:%.*]], i32* [[P:%.*]], i32* null
-; CHECK-NEXT:    ret i32* [[RES]]
+; CHECK-NEXT:    call void @llvm.assume(i1 [[COND:%.*]])
+; CHECK-NEXT:    ret i32* [[P:%.*]]
 ;
   %res = select i1 %cond, i32* %p, i32* null
   ret i32* %res
@@ -47,8 +42,9 @@
 
 define nonnull noundef i32* @nonnull_noundef_ret2(i1 %cond, i32* %p) {
 ; CHECK-LABEL: @nonnull_noundef_ret2(
-; CHECK-NEXT:    [[RES:%.*]] = select i1 [[COND:%.*]], i32* null, i32* [[P:%.*]]
-; CHECK-NEXT:    ret i32* [[RES]]
+; CHECK-NEXT:    [[TMP1:%.*]] = xor i1 [[COND:%.*]], true
+; CHECK-NEXT:    call void @llvm.assume(i1 [[TMP1]])
+; CHECK-NEXT:    ret i32* [[P:%.*]]
 ;
   %res = select i1 %cond, i32* null, i32* %p
   ret i32* %res
@@ -57,8 +53,7 @@
 
 define void @nonnull_call(i1 %cond, i32* %p) {
 ; CHECK-LABEL: @nonnull_call(
-; CHECK-NEXT:    [[RES:%.*]] = select i1 [[COND:%.*]], i32* [[P:%.*]], i32* null
-; CHECK-NEXT:    call void @f(i32* nonnull [[RES]])
+; CHECK-NEXT:    call void @f(i32* nonnull [[P:%.*]])
 ; CHECK-NEXT:    ret void
 ;
   %res = select i1 %cond, i32* %p, i32* null
@@ -68,8 +63,7 @@
 
 define void @nonnull_call2(i1 %cond, i32* %p) {
 ; CHECK-LABEL: @nonnull_call2(
-; CHECK-NEXT:    [[RES:%.*]] = select i1 [[COND:%.*]], i32* null, i32* [[P:%.*]]
-; CHECK-NEXT:    call void @f(i32* nonnull [[RES]])
+; CHECK-NEXT:    call void @f(i32* nonnull [[P:%.*]])
 ; CHECK-NEXT:    ret void
 ;
   %res = select i1 %cond, i32* null, i32* %p
@@ -79,8 +73,8 @@
 
 define void @nonnull_noundef_call(i1 %cond, i32* %p) {
 ; CHECK-LABEL: @nonnull_noundef_call(
-; CHECK-NEXT:    [[RES:%.*]] = select i1 [[COND:%.*]], i32* [[P:%.*]], i32* null
-; CHECK-NEXT:    call void @f(i32* noundef nonnull [[RES]])
+; CHECK-NEXT:    call void @llvm.assume(i1 [[COND:%.*]])
+; CHECK-NEXT:    call void @f(i32* noundef nonnull [[P:%.*]])
 ; CHECK-NEXT:    ret void
 ;
   %res = select i1 %cond, i32* %p, i32* null
@@ -90,8 +84,9 @@
 
 define void @nonnull_noundef_call2(i1 %cond, i32* %p) {
 ; CHECK-LABEL: @nonnull_noundef_call2(
-; CHECK-NEXT:    [[RES:%.*]] = select i1 [[COND:%.*]], i32* null, i32* [[P:%.*]]
-; CHECK-NEXT:    call void @f(i32* noundef nonnull [[RES]])
+; CHECK-NEXT:    [[TMP1:%.*]] = xor i1 [[COND:%.*]], true
+; CHECK-NEXT:    call void @llvm.assume(i1 [[TMP1]])
+; CHECK-NEXT:    call void @f(i32* noundef nonnull [[P:%.*]])
 ; CHECK-NEXT:    ret void
 ;
   %res = select i1 %cond, i32* null, i32* %p