[OpenCL] Generate opaque type for sampler_t and function call for the initializer

Currently Clang use int32 to represent sampler_t, which have been a source of issue for some backends, because in some backends sampler_t cannot be represented by int32. They have to depend on kernel argument metadata and use IPA to find the sampler arguments and global variables and transform them to target specific sampler type.

This patch uses opaque pointer type opencl.sampler_t* for sampler_t. For each use of file-scope sampler variable, it generates a function call of __translate_sampler_initializer. For each initialization of function-scope sampler variable, it generates a function call of __translate_sampler_initializer.

Each builtin library can implement its own __translate_sampler_initializer(). Since the real sampler type tends to be architecture dependent, allowing it to be initialized by a library function simplifies backend design. A typical implementation of __translate_sampler_initializer could be a table lookup of real sampler literal values. Since its argument is always a literal, the returned pointer is known at compile time and easily optimized to finally become some literal values directly put into image read instructions.

This patch is partially based on Alexey Sotkin's work in Khronos Clang (https://github.com/KhronosGroup/SPIR/commit/3d4eec61623502fc306e8c67c9868be2b136e42b).

Differential Revision: https://reviews.llvm.org/D21567

llvm-svn: 277024

1 files changed, 83 insertions, 8 deletions

diff --git a/clang/lib/Sema/SemaInit.cpp b/clang/lib/Sema/SemaInit.cpp
index af7fdc40c7b..fc896941df0 100644
--- a/clang/lib/Sema/SemaInit.cpp
+++ b/clang/lib/Sema/SemaInit.cpp
@@ -4885,7 +4885,8 @@ static bool TryOCLSamplerInitialization(Sema &S,
                                         QualType DestType,
                                         Expr *Initializer) {
   if (!S.getLangOpts().OpenCL || !DestType->isSamplerT() ||
-    !Initializer->isIntegerConstantExpr(S.getASTContext()))
+      (!Initializer->isIntegerConstantExpr(S.Context) &&
+      !Initializer->getType()->isSamplerT()))
     return false;
 
   Sequence.AddOCLSamplerInitStep(DestType);
@@ -6903,19 +6904,93 @@ InitializationSequence::Perform(Sema &S,
     }
 
     case SK_OCLSamplerInit: {
-      assert(Step->Type->isSamplerT() && 
+      // Sampler initialzation have 5 cases:
+      //   1. function argument passing
+      //      1a. argument is a file-scope variable
+      //      1b. argument is a function-scope variable
+      //      1c. argument is one of caller function's parameters
+      //   2. variable initialization
+      //      2a. initializing a file-scope variable
+      //      2b. initializing a function-scope variable
+      //
+      // For file-scope variables, since they cannot be initialized by function
+      // call of __translate_sampler_initializer in LLVM IR, their references
+      // need to be replaced by a cast from their literal initializers to
+      // sampler type. Since sampler variables can only be used in function
+      // calls as arguments, we only need to replace them when handling the
+      // argument passing.
+      assert(Step->Type->isSamplerT() &&
              "Sampler initialization on non-sampler type.");
-
-      QualType SourceType = CurInit.get()->getType();
-
+      Expr *Init = CurInit.get();
+      QualType SourceType = Init->getType();
+      // Case 1
       if (Entity.isParameterKind()) {
-        if (!SourceType->isSamplerT())
+        if (!SourceType->isSamplerT()) {
           S.Diag(Kind.getLocation(), diag::err_sampler_argument_required)
             << SourceType;
-      } else if (Entity.getKind() != InitializedEntity::EK_Variable) {
-        llvm_unreachable("Invalid EntityKind!");
+          break;
+        } else if (const DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(Init)) {
+          auto Var = cast<VarDecl>(DRE->getDecl());
+          // Case 1b and 1c
+          // No cast from integer to sampler is needed.
+          if (!Var->hasGlobalStorage()) {
+            CurInit = ImplicitCastExpr::Create(S.Context, Step->Type,
+                                               CK_LValueToRValue, Init,
+                                               /*BasePath=*/nullptr, VK_RValue);
+            break;
+          }
+          // Case 1a
+          // For function call with a file-scope sampler variable as argument,
+          // get the integer literal.
+          // Do not diagnose if the file-scope variable does not have initializer
+          // since this has already been diagnosed when parsing the variable
+          // declaration.
+          if (!Var->getInit() || !isa<ImplicitCastExpr>(Var->getInit()))
+            break;
+          Init = cast<ImplicitCastExpr>(const_cast<Expr*>(
+            Var->getInit()))->getSubExpr();
+          SourceType = Init->getType();
+        }
+      } else {
+        // Case 2
+        // Check initializer is 32 bit integer constant.
+        // If the initializer is taken from global variable, do not diagnose since
+        // this has already been done when parsing the variable declaration.
+        if (!Init->isConstantInitializer(S.Context, false))
+          break;
+        
+        if (!SourceType->isIntegerType() ||
+            32 != S.Context.getIntWidth(SourceType)) {
+          S.Diag(Kind.getLocation(), diag::err_sampler_initializer_not_integer)
+            << SourceType;
+          break;
+        }
+
+        llvm::APSInt Result;
+        Init->EvaluateAsInt(Result, S.Context);
+        const uint64_t SamplerValue = Result.getLimitedValue();
+        // 32-bit value of sampler's initializer is interpreted as
+        // bit-field with the following structure:
+        // |unspecified|Filter|Addressing Mode| Normalized Coords|
+        // |31        6|5    4|3             1|                 0|
+        // This structure corresponds to enum values of sampler properties
+        // defined in SPIR spec v1.2 and also opencl-c.h
+        unsigned AddressingMode  = (0x0E & SamplerValue) >> 1;
+        unsigned FilterMode      = (0x30 & SamplerValue) >> 4;
+        if (FilterMode != 1 && FilterMode != 2)
+          S.Diag(Kind.getLocation(),
+                 diag::warn_sampler_initializer_invalid_bits)
+                 << "Filter Mode";
+        if (AddressingMode > 4)
+          S.Diag(Kind.getLocation(),
+                 diag::warn_sampler_initializer_invalid_bits)
+                 << "Addressing Mode";
       }
 
+      // Cases 1a, 2a and 2b
+      // Insert cast from integer to sampler.
+      CurInit = S.ImpCastExprToType(Init, S.Context.OCLSamplerTy,
+                                      CK_IntToOCLSampler);
       break;
     }
     case SK_OCLZeroEvent: {