From 0ef3d3b429030ebd26d762e6dd945bc00f5ab6f8 Mon Sep 17 00:00:00 2001
From: Vsevolod Livinskiy <vsevolod.livinskij@frtk.ru>
Date: Fri, 5 Feb 2016 14:49:42 +0300
Subject: [PATCH] Define dereferencing varying pointer to uniform struct with
 'bound uniform' member.

---
 ctx.cpp                    | 40 +++++++++++++++++++++++++++++++++++---
 ctx.h                      |  3 ++-
 tests/struct-test-127.ispc | 37 +++++++++++++++++++++++++++++++++++
 3 files changed, 76 insertions(+), 4 deletions(-)
 create mode 100644 tests/struct-test-127.ispc

diff --git a/ctx.cpp b/ctx.cpp
index 367ec381..d0aa9ef2 100644
--- a/ctx.cpp
+++ b/ctx.cpp
@@ -2805,7 +2805,8 @@ FunctionEmitContext::loadUniformFromSOA(llvm::Value *ptr, llvm::Value *mask,
 
 llvm::Value *
 FunctionEmitContext::LoadInst(llvm::Value *ptr, llvm::Value *mask,
-                              const Type *ptrRefType, const char *name) {
+                              const Type *ptrRefType, const char *name, 
+                              bool one_elem) {
     if (ptr == NULL) {
         AssertPos(currentPos, m->errorCount > 0);
         return NULL;
@@ -2861,7 +2862,33 @@ FunctionEmitContext::LoadInst(llvm::Value *ptr, llvm::Value *mask,
     else {
         // Otherwise we should have a varying ptr and it's time for a
         // gather.
-        return gather(ptr, ptrType, GetFullMask(), name);
+        llvm::Value *gather_result =  gather(ptr, ptrType, GetFullMask(), name);
+        if (!one_elem)
+            return gather_result;
+
+        // It is a kludge. When we dereference varying pointer to uniform struct
+        // with "bound uniform" member, we should return first unmasked member.
+        Warning(currentPos, "Dereferencing varying pointer to uniform struct with 'bound uniform' member,\n"
+                     " only one value will survive. Possible loss of data.");
+        // Call the target-dependent movmsk function to turn the vector mask
+        // into an i64 value
+        std::vector<Symbol *> mm;
+        m->symbolTable->LookupFunction("__movmsk", &mm);
+        if (g->target->getMaskBitCount() == 1)
+            AssertPos(currentPos, mm.size() == 1);
+        else
+            // There should be one with signed int signature, one unsigned int.
+            AssertPos(currentPos, mm.size() == 2);
+        // We can actually call either one, since both are i32s as far as
+        // LLVM's type system is concerned...
+        llvm::Function *fmm = mm[0]->function;
+        llvm::Value *int_mask =  CallInst(fmm, NULL, mask, LLVMGetName(mask, "_movmsk"));
+        std::vector<Symbol *> lz;
+        m->symbolTable->LookupFunction("__count_trailing_zeros_i64", &lz);
+        llvm::Function *flz = lz[0]->function;
+        llvm::Value *elem_idx = CallInst(flz, NULL, int_mask, LLVMGetName(mask, "_clz"));
+        llvm::Value *elem = llvm::ExtractElementInst::Create(gather_result, elem_idx, LLVMGetName(gather_result, "_umasked_elem"), bblock);
+        return elem;
     }
 }
 
@@ -2882,6 +2909,9 @@ FunctionEmitContext::gather(llvm::Value *ptr, const PointerType *ptrType,
         // result.
         llvm::Value *retValue = llvm::UndefValue::get(llvmReturnType);
 
+        const CollectionType *returnCollectionType =
+            CastType<CollectionType>(returnType->GetBaseType());
+
         for (int i = 0; i < collectionType->GetElementCount(); ++i) {
             const PointerType *eltPtrType;
             llvm::Value *eltPtr =
@@ -2889,8 +2919,12 @@ FunctionEmitContext::gather(llvm::Value *ptr, const PointerType *ptrType,
 
             eltPtr = addVaryingOffsetsIfNeeded(eltPtr, eltPtrType);
 
+            // It is a kludge. When we dereference varying pointer to uniform struct
+            // with "bound uniform" member, we should return first unmasked member.
+            int need_one_elem = CastType<StructType>(ptrType->GetBaseType()) &&
+                                returnCollectionType->GetElementType(i)->IsUniformType();
             // This in turn will be another gather
-            llvm::Value *eltValues = LoadInst(eltPtr, mask, eltPtrType, name);
+            llvm::Value *eltValues = LoadInst(eltPtr, mask, eltPtrType, name, need_one_elem);
 
             retValue = InsertInst(retValue, eltValues, i, "set_value");
         }
diff --git a/ctx.h b/ctx.h
index 3f52cdc4..dff5f3ec 100644
--- a/ctx.h
+++ b/ctx.h
@@ -481,7 +481,8 @@ public:
         pointer values given by the lvalue.  If the lvalue is not varying,
         then both the mask pointer and the type pointer may be NULL. */
     llvm::Value *LoadInst(llvm::Value *ptr, llvm::Value *mask,
-                          const Type *ptrType, const char *name = NULL);
+                          const Type *ptrType, const char *name = NULL, 
+                          bool one_elem = false);
 
     llvm::Value *LoadInst(llvm::Value *ptr, const char *name = NULL);
 
diff --git a/tests/struct-test-127.ispc b/tests/struct-test-127.ispc
new file mode 100644
index 00000000..75e04498
--- /dev/null
+++ b/tests/struct-test-127.ispc
@@ -0,0 +1,37 @@
+
+export uniform int width() { return programCount; }
+
+
+struct Foo {
+    uniform float x;
+    varying float y;
+};
+
+inline varying Foo func(uniform Foo * varying f)
+{
+    return *f;
+}
+
+export void f_fu(uniform float RET[], uniform float aFOO[], uniform float b) {
+    float a = aFOO[programIndex];
+    uniform Foo struct_1;
+    struct_1.x = b;
+    struct_1.y = aFOO[programIndex];
+
+    uniform Foo * varying ptr = &(struct_1);
+    varying Foo struct_2;
+    struct_2.x = -100;
+    struct_2.y = -150;
+    if (programIndex % 3 == 0)
+        struct_2 = func(ptr);
+    RET[programIndex] = struct_2.x + struct_2.y;
+}
+
+
+export void result(uniform float RET[]) {
+    if (programIndex % 3 == 0)
+        RET[programIndex] = 5 + programIndex + 1;
+    else
+        RET[programIndex] = -145;
+}
+