[OpenCL] Handle address space conversions for constexpr (PR44177)

[svenvh]

Summary

The AST for the constexpr.cl test contains address space conversion
nodes to cast through the implicit generic address space. These
caused the evaluator to reject the input as constexpr in C++ for
OpenCL mode, whereas the input was considered constexpr in plain C++
mode.

[Anastasia]

LGTM! Thanks!

clang/lib/AST/ExprConstant.cpp

bool VisitCastExpr(const CastExpr *E) {
     case CK_LValueToRValueBitCast: {
       APValue DestValue, SourceValue;
       if (!Evaluate(SourceValue, Info, E->getSubExpr()))
         return false;
       if (!handleLValueToRValueBitCast(Info, DestValue, SourceValue, E))
         return false;
       return DerivedSuccess(DestValue, E);
     }
+
+    case CK_AddressSpaceConversion: {
+      APValue Value;
+      if (!Evaluate(Value, Info, E->getSubExpr()))
+        return false;
+      return DerivedSuccess(Value, E);
+    }
     }
 
     return Error(E);
   }
 
   bool VisitUnaryPostInc(const UnaryOperator *UO) {
     return VisitUnaryPostIncDec(UO);
   }

clang/test/CodeGenOpenCLCXX/address-space-deduction.cl

 // RUN: %clang_cc1 %s -triple spir-unknown-unknown -cl-std=clc++ -O0 -emit-llvm -o - | FileCheck %s -check-prefixes=COMMON,PTR
 // RUN: %clang_cc1 %s -triple spir-unknown-unknown -cl-std=clc++ -O0 -emit-llvm -o - -DREF | FileCheck %s -check-prefixes=COMMON,REF
 
 #ifdef REF
 #define PTR &
 #define ADR(x) x
 #else
 #define PTR *
 #define ADR(x) &x
 #endif
 
 //COMMON: @glob = addrspace(1) global i32
 int glob;
 //PTR: @glob_p = addrspace(1) global i32 addrspace(4)* addrspacecast (i32 addrspace(1)* @glob to i32 addrspace(4)*)
-//REF: @glob_p = addrspace(1) global i32 addrspace(4)* null
+//REF: @glob_p = addrspace(1) constant i32 addrspace(4)* addrspacecast (i32 addrspace(1)* @glob to i32 addrspace(4)*)
 int PTR glob_p = ADR(glob);
 
 //COMMON: @_ZZ3fooi{{P|R}}U3AS4iE6loc_st = internal addrspace(1) global i32
 //PTR: @_ZZ3fooiPU3AS4iE8loc_st_p = internal addrspace(1) global i32 addrspace(4)* addrspacecast (i32 addrspace(1)* @_ZZ3fooiPU3AS4iE6loc_st to i32 addrspace(4)*)
-//REF: @_ZZ3fooiRU3AS4iE8loc_st_p = internal addrspace(1) global i32 addrspace(4)* null
+//REF: @_ZZ3fooiRU3AS4iE8loc_st_p = internal addrspace(1) constant i32 addrspace(4)* addrspacecast (i32 addrspace(1)* @_ZZ3fooiRU3AS4iE6loc_st to i32 addrspace(4)*)
 //COMMON: @loc_ext_p = external addrspace(1) {{global|constant}} i32 addrspace(4)*
 //COMMON: @loc_ext = external addrspace(1) global i32
 
-//REF: store i32 addrspace(4)* addrspacecast (i32 addrspace(1)* @glob to i32 addrspace(4)*), i32 addrspace(4)* addrspace(1)* @glob_p
-
 //COMMON: define spir_func i32 @_Z3fooi{{P|R}}U3AS4i(i32 %par, i32 addrspace(4)*{{.*}} %par_p)
 int foo(int par, int PTR par_p){
   //COMMON: %loc = alloca i32
   int loc;
   //COMMON: %loc_p = alloca i32 addrspace(4)*
   //COMMON: %loc_p_const = alloca i32*
   //COMMON: [[GAS:%[._a-z0-9]*]] = addrspacecast i32* %loc to i32 addrspace(4)*
   //COMMON: store i32 addrspace(4)* [[GAS]], i32 addrspace(4)** %loc_p
   int PTR loc_p = ADR(loc);
   //COMMON: store i32* %loc, i32** %loc_p_const
   const __private int PTR loc_p_const = ADR(loc);
 
   // CHECK directives for the following code are located above.
   static int loc_st;
-  //REF: store i32 addrspace(4)* addrspacecast (i32 addrspace(1)* @_ZZ3fooiRU3AS4iE6loc_st to i32 addrspace(4)*), i32 addrspace(4)* addrspace(1)* @_ZZ3fooiRU3AS4iE8loc_st_p
   static int PTR loc_st_p = ADR(loc_st);
   extern int loc_ext;
   extern int PTR loc_ext_p;
   (void)loc_ext_p;
   return loc_ext;
 }

clang/test/CodeGenOpenCLCXX/constexpr.cl

+// RUN: %clang_cc1 %s -triple spir-unknown-unknown -cl-std=clc++ -O0 -emit-llvm -o - | FileCheck %s
+
+struct Storage final {
+  constexpr const float& operator[](const int index) const noexcept {
+    return InternalStorage[index];
+  }
+
+  const float InternalStorage[1];
+};
+
+constexpr Storage getStorage() {
+  return Storage{{1.0f}};
+}
+
+constexpr float compute() {
+  constexpr auto s = getStorage();
+  return 2.0f / (s[0]);
+}
+
+constexpr float FloatConstant = compute();
+
+// CHECK-LABEL: define spir_kernel void @foo
+// CHECK: store float 2.000000e+00
+kernel void foo(global float *x) {
+  *x = FloatConstant;
+}