If a ptr arg is misaligned (ptr to 8bit/16bit, etc), we must

use buffer offset to convert them to stateful; otherwise, they
must remain stateless.

This is due to the fact that surface state's base must be DW-aligned.
This bug was not exposed in ocl tests (probably due to less coverage).

THis code is off by default now.

Change-Id: I4721642454ad74559a47ff8afbf115100efc2e34

IGC/Compiler/Optimizer/OpenCLPasses/StatelessToStatefull/StatelessToStatefull.cpp

@@ -338,6 +338,20 @@ bool StatelessToStatefull::getOffsetFromGEP(
 bool StatelessToStatefull::pointerIsPositiveOffsetFromKernelArgument(
     Function* F, Value* V, Value*& offset, unsigned int& argNumber)
 {
+    auto getPointeeAlign = [](const DataLayout* DL, Value* ptrVal)-> unsigned {
+        if (PointerType* PTy = dyn_cast<PointerType>(ptrVal->getType()))
+        {
+            Type* pointeeTy = PTy->getElementType();
+            if (!pointeeTy->isSized()) {
+                return 0;
+            }
+            return DL->getABITypeAlignment(pointeeTy);
+        }
+        return 0;
+    };
+
+    const DataLayout* DL = &F->getParent()->getDataLayout();
+
     AssumptionCache* AC = getAC(F);
 
     PointerType* ptrType = dyn_cast<PointerType>(V->getType());
@@ -370,18 +384,38 @@ bool StatelessToStatefull::pointerIsPositiveOffsetFromKernelArgument(
             argNumber = arg->getAssociatedArgNo();
             bool gepProducesPositivePointer = true;
 
+            // An address needs to be DW-aligned in order to be a base
+            // in a surface state.  In another word, a unaligned argument
+            // cannot be used as a surface base unless buffer_offset is
+            // used, in which "argument + buffer_offset" is instead used
+            // as a surface base. (argument + buffer_offset is the original
+            // base of buffer created on host side, the original buffer is
+            // guarantted to be DW-aligned.)
+            //
+            // Note that implicit arg is always aligned.
+            bool isAlignedPointee =
+                (IGC_IS_FLAG_DISABLED(UseSubDWAlignedPtrArg) || arg->isImplicitArg())
+                ? true
+                : (getPointeeAlign(DL, base) >= 4);
+
             // If m_hasBufferOffsetArg is true, the offset argument is added to
-            // the final offset, and the final offset must be positive. Thus
-            // skip checking if an offset is positive.
+            // the final offset to make it definitely positive. Thus skip checking
+            // if an offset is positive.
+            //
+            // Howerver, if m_hasoptionalBufferOffsetArg is true, the buffer offset
+            // is not generated if all offsets can be proven positive (this has
+            // performance benefit as adding buffer offset is an additional add).
+            // Also, if an argument is unaligned, buffer offset must be ON and used;
+            // otherwise, no stateful conversion for the argument can be carried out.
             //
-            // Note that offset should be positive for any implicit ptr argument
+            // Note that offset should be positive for any implicit ptr argument,
+            // so no need to prove it!
             if (!arg->isImplicitArg() &&
+                isAlignedPointee &&
                 (!m_hasBufferOffsetArg || m_hasOptionalBufferOffsetArg) &&
                 IGC_IS_FLAG_DISABLED(SToSProducesPositivePointer))
             {
-                // [This is conservative path]
-                // Need to verify if there is a negative offset,
-                // If so, no stateful message is generated.
+                // This is for proving that the offset is positive.
                 for (int i = 0, sz = GEPs.size(); i < sz; ++i)
                 {
                     GetElementPtrInst* tgep = GEPs[i];
@@ -398,7 +432,8 @@ bool StatelessToStatefull::pointerIsPositiveOffsetFromKernelArgument(
                     updateArgInfo(arg, gepProducesPositivePointer);
                 }
             }
-            if ((gepProducesPositivePointer || m_hasBufferOffsetArg) &&
+            if ((m_hasBufferOffsetArg ||
+                 (gepProducesPositivePointer && isAlignedPointee)) &&
                 getOffsetFromGEP(F, GEPs, argNumber, arg->isImplicitArg(), offset))
             {
                 return true;

IGC/common/igc_flags.def

@@ -196,8 +196,9 @@ DECLARE_IGC_REGKEY(debugString, SIPOverrideFilePath,    0,     "This key when en
 DECLARE_IGC_REGKEY(bool, DumpPayloadToScratch,          false, "Setting this to 1/true dumps thread payload to scartch space. Used for  workloads which doesnt use scartch space for other purposes", false)
 DECLARE_IGC_REGKEY(DWORD, DebugInternalSwitch,          0,     "Code pass selection, debug only", false)
 DECLARE_IGC_REGKEY(bool, SToSProducesPositivePointer,   false, "This key is for StatelessToStatefull optimization if the  user knows the pointer offset is postive to the kernel argument.", false)
-DECLARE_IGC_REGKEY(bool, EnableSupportBufferOffset,     false, "[Temporary]For StatelessToStatefull optimization [OCL], support implicit buffer offset argument (same as -cl-intel-has-buffer-offset-arg).", false)
-DECLARE_IGC_REGKEY(bool, EnableOptionalBufferOffset,    true,  "[Temporary]For StatelessToStatefull optimization [OCL], if true, make buffer offset optional. Valid only if buffer offset is supported.", true)
+DECLARE_IGC_REGKEY(bool, EnableSupportBufferOffset,     false, "[debugging]For StatelessToStatefull optimization [OCL], support implicit buffer offset argument (same as -cl-intel-has-buffer-offset-arg).", false)
+DECLARE_IGC_REGKEY(bool, EnableOptionalBufferOffset,    true,  "For StatelessToStatefull optimization [OCL], if true, make buffer offset optional. Valid only if buffer offset is supported.", true)
+DECLARE_IGC_REGKEY(bool, UseSubDWAlignedPtrArg,         false, "[OCL]If set, for kernel pointer arg such as ptr to char or short, the arg is not necessarily DW aligned", false)
 DECLARE_IGC_REGKEY(bool, EnableTestIGCBuiltin,          false, "Enable testing igc builtin (precompiled kernels) using OCL.", false)
 DECLARE_IGC_REGKEY(bool, EnableCSSIMD32,                false, "Enable computer shader SIMD32 mode, and fall back to lower SIMD when spill", false)
 DECLARE_IGC_REGKEY(bool, ForceCSSIMD32,                 false, "Force computer shader SIMD32 mode", false)