Index: lib/Transforms/IPO/IPConstantPropagation.cpp
===================================================================
--- lib/Transforms/IPO/IPConstantPropagation.cpp
+++ lib/Transforms/IPO/IPConstantPropagation.cpp
@@ -66,6 +66,13 @@
     if (!ACS)
       return false;
 
+    // Mismatched argument count is undefined behavior. Simply bail out to avoid
+    // handling of such situations below (avoiding asserts/crashes).
+    unsigned NumActualArgs = ACS.getNumArgOperands();
+    if (F.isVarArg() ? ArgumentConstants.size() > NumActualArgs
+                     : ArgumentConstants.size() != NumActualArgs)
+      return false;
+
     // Check out all of the potentially constant arguments.  Note that we don't
     // inspect varargs here.
     Function::arg_iterator Arg = F.arg_begin();
@@ -78,6 +85,11 @@
       Value *V = ACS.getCallArgOperand(i);
       Constant *C = dyn_cast_or_null<Constant>(V);
 
+      // Mismatched argument type is undefined behavior. Simply bail out to avoid
+      // handling of such situations below (avoiding asserts/crashes).
+      if (C && Arg->getType() != C->getType())
+        return false;
+
       // We can only propagate thread independent values through callbacks.
       // This is different to direct/indirect call sites because for them we
       // know the thread executing the caller and callee is the same. For
Index: test/Transforms/IPConstantProp/arg-count-mismatch.ll
===================================================================
--- /dev/null
+++ test/Transforms/IPConstantProp/arg-count-mismatch.ll
@@ -0,0 +1,72 @@
+; RUN: opt < %s -ipconstprop -S -o - | FileCheck %s
+
+; The original C source looked like this:
+;
+;   long long a101, b101, e101;
+;   volatile long c101;
+;   int d101;
+;
+;   static inline int bar(p1, p2)
+;   {
+;       return 0;
+;   }
+;
+;   void foo(unsigned p1)
+;   {
+;       long long *f = &b101, *g = &e101;
+;       c101 = 0;
+;       (void)((*f |= a101) - (*g = bar(d101)));
+;       c101 = (*f |= a101 &= p1) == d101;
+;   }
+;
+; When compiled with Clang it gives a warning
+;   warning: too few arguments in call to 'bar'
+;
+; This ll reproducer has been reduced to only include tha call.
+;
+; Note that -lint will report this as UB, but it passes -verify.
+
+; This test is just to verify that we do not crash/assert due to mismatch in
+; argument count between the caller and callee.
+
+define dso_local void @foo(i16 %a) {
+; CHECK-LABEL: @foo(
+; CHECK-NEXT:    [[CALL:%.*]] = call i16 bitcast (i16 (i16, i16)* @bar to i16 (i16)*)(i16 [[A:%.*]])
+; CHECK-NEXT:    ret void
+;
+  %call = call i16 bitcast (i16 (i16, i16) * @bar to i16 (i16) *)(i16 %a)
+  ret void
+}
+
+define internal i16 @bar(i16 %p1, i16 %p2) {
+; CHECK-LABEL: @bar(
+; CHECK-NEXT:    ret i16 0
+;
+  ret i16 0
+}
+
+;-------------------------------------------------------------------------------
+; Additional tests to verify that we still optimize when having a mismatch
+; in argument count due to varargs (as long as all non-variadic arguments have
+; been provided),
+
+define dso_local void @vararg_tests(i16 %a) {
+  %call1 = call i16 (i16, ...) @vararg_prop(i16 7, i16 8, i16 %a)
+  %call2 = call i16 bitcast (i16 (i16, i16, ...) * @vararg_no_prop to i16 (i16) *) (i16 7)
+  ret void
+}
+
+define internal i16 @vararg_prop(i16 %p1, ...) {
+; CHECK-LABEL: define internal i16 @vararg_prop(
+; CHECK-NEXT:    ret i16 7
+;
+  ret i16 %p1
+}
+
+define internal i16 @vararg_no_prop(i16 %p1, i16 %p2, ...) {
+; CHECK-LABEL: define internal i16 @vararg_no_prop(
+; CHECK-NEXT:    ret i16 [[P1:%.*]]
+;
+  ret i16 %p1
+}
+
Index: test/Transforms/IPConstantProp/arg-type-mismatch.ll
===================================================================
--- /dev/null
+++ test/Transforms/IPConstantProp/arg-type-mismatch.ll
@@ -0,0 +1,23 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -ipconstprop -S -o - | FileCheck %s
+
+; This test is just to verify that we do not crash/assert due to mismatch in
+; argument type between the caller and callee.
+
+define dso_local void @foo(i16 %a) {
+; CHECK-LABEL: @foo(
+; CHECK-NEXT:    [[CALL:%.*]] = call i16 bitcast (i16 (i16, i16)* @bar to i16 (i16, i32)*)(i16 [[A:%.*]], i32 7)
+; CHECK-NEXT:    ret void
+;
+  %call = call i16 bitcast (i16 (i16, i16) * @bar to i16 (i16, i32) *)(i16 %a, i32 7)
+  ret void
+}
+
+define internal i16 @bar(i16 %p1, i16 %p2) {
+; CHECK-LABEL: @bar(
+; CHECK-NEXT:    ret i16 [[P2:%.*]]
+;
+  ret i16 %p2
+}
+
+