diff --git a/clang/test/CodeGenOpenCL/overload.cl b/clang/test/CodeGenOpenCL/overload.cl
--- a/clang/test/CodeGenOpenCL/overload.cl
+++ b/clang/test/CodeGenOpenCL/overload.cl
@@ -1,5 +1,5 @@
-// RUN: %clang_cc1 -no-opaque-pointers -cl-std=CL2.0 -emit-llvm -o - -triple spir-unknown-unknown %s | FileCheck %s
-// RUN: %clang_cc1 -no-opaque-pointers -cl-std=CL3.0 -cl-ext=+__opencl_c_generic_address_space -emit-llvm -o - -triple spir-unknown-unknown %s | FileCheck %s
+// RUN: %clang_cc1 -disable-llvm-passes -no-opaque-pointers -cl-std=CL2.0 -emit-llvm -o - -triple spir-unknown-unknown %s | FileCheck %s
+// RUN: %clang_cc1 -disable-llvm-passes -no-opaque-pointers -cl-std=CL3.0 -cl-ext=+__opencl_c_generic_address_space -emit-llvm -o - -triple spir-unknown-unknown %s | FileCheck %s
 
 typedef short short4 __attribute__((ext_vector_type(4)));
 
@@ -21,18 +21,18 @@
   generic int *generic *gengen;
   generic int *local *genloc;
   generic int *global *genglob;
-  // CHECK-DAG: call spir_func void @_Z3fooPU3AS1iS0_(i32 addrspace(1)* noundef undef, i32 addrspace(1)* noundef undef)
+  // CHECK-DAG: call spir_func void @_Z3fooPU3AS1iS0_(i32 addrspace(1)* noundef {{.*}}, i32 addrspace(1)* noundef {{.*}})
   foo(a, b);
-  // CHECK-DAG: call spir_func void @_Z3fooPU3AS4iS0_(i32 addrspace(4)* noundef undef, i32 addrspace(4)* noundef undef)
+  // CHECK-DAG: call spir_func void @_Z3fooPU3AS4iS0_(i32 addrspace(4)* noundef {{.*}}, i32 addrspace(4)* noundef {{.*}})
   foo(b, c);
-  // CHECK-DAG: call spir_func void @_Z3fooPU3AS4iS0_(i32 addrspace(4)* noundef undef, i32 addrspace(4)* noundef undef)
+  // CHECK-DAG: call spir_func void @_Z3fooPU3AS4iS0_(i32 addrspace(4)* noundef {{.*}}, i32 addrspace(4)* noundef {{.*}})
   foo(a, d);
 
-  // CHECK-DAG: call spir_func void @_Z3barPU3AS4PU3AS4iS2_(i32 addrspace(4)* addrspace(4)* noundef undef, i32 addrspace(4)* addrspace(4)* noundef undef)
+  // CHECK-DAG: call spir_func void @_Z3barPU3AS4PU3AS4iS2_(i32 addrspace(4)* addrspace(4)* noundef {{.*}}, i32 addrspace(4)* addrspace(4)* noundef {{.*}})
   bar(gengen, genloc);
-  // CHECK-DAG: call spir_func void @_Z3barPU3AS4PU3AS4iS2_(i32 addrspace(4)* addrspace(4)* noundef undef, i32 addrspace(4)* addrspace(4)* noundef undef)
+  // CHECK-DAG: call spir_func void @_Z3barPU3AS4PU3AS4iS2_(i32 addrspace(4)* addrspace(4)* noundef {{.*}}, i32 addrspace(4)* addrspace(4)* noundef {{.*}})
   bar(gengen, genglob);
-  // CHECK-DAG: call spir_func void @_Z3barPU3AS1PU3AS4iS2_(i32 addrspace(4)* addrspace(1)* noundef undef, i32 addrspace(4)* addrspace(1)* noundef undef)
+  // CHECK-DAG: call spir_func void @_Z3barPU3AS1PU3AS4iS2_(i32 addrspace(4)* addrspace(1)* noundef {{.*}}, i32 addrspace(4)* addrspace(1)* noundef {{.*}})
   bar(genglob, genglob);
 }
 
@@ -40,8 +40,8 @@
 void kernel test2() {
   short4 e0=0;
 
-  // CHECK-DAG: call spir_func <4 x i16> @_Z5clampDv4_sss(<4 x i16> noundef zeroinitializer, i16 noundef signext 0, i16 noundef signext 255)
+  // CHECK-DAG: call spir_func <4 x i16> @_Z5clampDv4_sss(<4 x i16> noundef {{.*}}, i16 noundef signext 0, i16 noundef signext 255)
   clamp(e0, 0, 255);
-  // CHECK-DAG: call spir_func <4 x i16> @_Z5clampDv4_sS_S_(<4 x i16> noundef zeroinitializer, <4 x i16> noundef zeroinitializer, <4 x i16> noundef zeroinitializer)
+  // CHECK-DAG: call spir_func <4 x i16> @_Z5clampDv4_sS_S_(<4 x i16> noundef {{.*}}, <4 x i16> noundef {{.*}}, <4 x i16> noundef {{.*}})
   clamp(e0, e0, e0);
 }
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
@@ -2900,6 +2900,15 @@
   return nullptr;
 }
 
+static bool callPassesUndefToPassingUndefUBParam(CallBase &Call) {
+  for (unsigned I = 0; I < Call.arg_size(); ++I) {
+    if (isa<UndefValue>(Call.getArgOperand(I)) && Call.isPassingUndefUB(I)) {
+      return true;
+    }
+  }
+  return false;
+}
+
 bool InstCombinerImpl::annotateAnyAllocSite(CallBase &Call,
                                             const TargetLibraryInfo *TLI) {
   // Note: We only handle cases which can't be driven from generic attributes
@@ -3026,9 +3035,11 @@
 
   // Calling a null function pointer is undefined if a null address isn't
   // dereferenceable.
+  // Passing undef/poison to any parameter where doing so is UB is undefined (of
+  // course).
   if ((isa<ConstantPointerNull>(Callee) &&
        !NullPointerIsDefined(Call.getFunction())) ||
-      isa<UndefValue>(Callee)) {
+      isa<UndefValue>(Callee) || callPassesUndefToPassingUndefUBParam(Call)) {
     // If Call does not return void then replaceInstUsesWith poison.
     // This allows ValueHandlers and custom metadata to adjust itself.
     if (!Call.getType()->isVoidTy())
diff --git a/llvm/test/Transforms/InstCombine/call-undef.ll b/llvm/test/Transforms/InstCombine/call-undef.ll
--- a/llvm/test/Transforms/InstCombine/call-undef.ll
+++ b/llvm/test/Transforms/InstCombine/call-undef.ll
@@ -8,7 +8,7 @@
 
 define void @test1() {
 ; CHECK-LABEL: @test1(
-; CHECK-NEXT:    call void @c(i32 undef)
+; CHECK-NEXT:    store i1 true, ptr poison, align 1
 ; CHECK-NEXT:    ret void
 ;
   call void @c(i32 undef)
@@ -17,7 +17,7 @@
 
 define void @test2() {
 ; CHECK-LABEL: @test2(
-; CHECK-NEXT:    call void @c(i32 poison)
+; CHECK-NEXT:    store i1 true, ptr poison, align 1
 ; CHECK-NEXT:    ret void
 ;
   call void @c(i32 poison)
@@ -26,7 +26,7 @@
 
 define void @test3() {
 ; CHECK-LABEL: @test3(
-; CHECK-NEXT:    call void @e(i32 noundef undef)
+; CHECK-NEXT:    store i1 true, ptr poison, align 1
 ; CHECK-NEXT:    ret void
 ;
   call void @e(i32 noundef undef)
@@ -35,7 +35,7 @@
 
 define void @test4() {
 ; CHECK-LABEL: @test4(
-; CHECK-NEXT:    call void @e(i32 noundef poison)
+; CHECK-NEXT:    store i1 true, ptr poison, align 1
 ; CHECK-NEXT:    ret void
 ;
   call void @e(i32 noundef poison)
@@ -44,7 +44,7 @@
 
 define void @test5() {
 ; CHECK-LABEL: @test5(
-; CHECK-NEXT:    call void @d(ptr undef)
+; CHECK-NEXT:    store i1 true, ptr poison, align 1
 ; CHECK-NEXT:    ret void
 ;
   call void @d(ptr undef)
@@ -53,7 +53,7 @@
 
 define void @test6() {
 ; CHECK-LABEL: @test6(
-; CHECK-NEXT:    call void @d(ptr poison)
+; CHECK-NEXT:    store i1 true, ptr poison, align 1
 ; CHECK-NEXT:    ret void
 ;
   call void @d(ptr poison)
@@ -62,7 +62,7 @@
 
 define void @test7() {
 ; CHECK-LABEL: @test7(
-; CHECK-NEXT:    call void @f(ptr dereferenceable(1) undef)
+; CHECK-NEXT:    store i1 true, ptr poison, align 1
 ; CHECK-NEXT:    ret void
 ;
   call void @f(ptr dereferenceable(1) undef)
@@ -71,7 +71,7 @@
 
 define void @test8() {
 ; CHECK-LABEL: @test8(
-; CHECK-NEXT:    call void @f(ptr dereferenceable(1) poison)
+; CHECK-NEXT:    store i1 true, ptr poison, align 1
 ; CHECK-NEXT:    ret void
 ;
   call void @f(ptr dereferenceable(1) poison)
diff --git a/llvm/test/Transforms/InstCombine/out-of-bounds-indexes.ll b/llvm/test/Transforms/InstCombine/out-of-bounds-indexes.ll
--- a/llvm/test/Transforms/InstCombine/out-of-bounds-indexes.ll
+++ b/llvm/test/Transforms/InstCombine/out-of-bounds-indexes.ll
@@ -6,7 +6,7 @@
 ; CHECK-LABEL: @test_out_of_bounds(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[AND1:%.*]] = and i32 [[A:%.*]], 3
-; CHECK-NEXT:    tail call void @llvm.assume(i1 poison)
+; CHECK-NEXT:    store i1 true, ptr poison, align 1
 ; CHECK-NEXT:    ret i32 [[AND1]]
 ;
 entry:
@@ -20,7 +20,7 @@
 define i128 @test_non64bit(i128 %a) {
 ; CHECK-LABEL: @test_non64bit(
 ; CHECK-NEXT:    [[AND1:%.*]] = and i128 [[A:%.*]], 3
-; CHECK-NEXT:    tail call void @llvm.assume(i1 poison)
+; CHECK-NEXT:    store i1 true, ptr poison, align 1
 ; CHECK-NEXT:    ret i128 [[AND1]]
 ;
   %and1 = and i128 %a, 3