[Autobackout][FuncReg]Revert of change: 8ca504f

When doing bitcast of immediate, if the dst type has the same size as the
original one, it is okay to regenerate imm with dst's type (exisiting code).
If the dst type is a vector type, we need to create a temp var, initialized
with the imm, and return the alias to the new temp var.

Also, simplify emitVectorBitcast to avoid potential redundant mov instructions
when src is immeidate.

Change-Id: Ibcf35d9317a6cf908a3427165ff7bb81648897e5

Author: jgu222

IGC/Compiler/CISACodeGen/CShader.cpp

@@ -857,31 +857,9 @@ CVariable* CShader::GetGlobalCVar(llvm::Value* value)
 CVariable* CShader::BitCast(CVariable* var, VISA_Type newType)
 {
     CVariable* bitCast = nullptr;
-    uint32_t newEltSz = CEncoder::GetCISADataTypeSize(newType);
-    uint32_t eltSz = var->GetElemSize();
-    // Bitcase requires both src and dst have the same size. Thus, they
-    // are either equal or one is a multiple of the other.
-    IGC_ASSERT(   (newEltSz >= eltSz && (newEltSz % eltSz) == 0)
-               || (newEltSz < eltSz && (eltSz% newEltSz) == 0));
     if (var->IsImmediate())
     {
-        if (newEltSz == eltSz)
-            bitCast = ImmToVariable(var->GetImmediateValue(), newType);
-        else
-        {
-            // Need a temp. For example,  bitcast i64 0 -> 2xi32
-            CVariable* tmp = GetNewVariable(
-                1,
-                var->GetType(),
-                CEncoder::GetCISADataTypeAlignment(var->GetType()),
-                true,
-                1,
-                "vecImmBitCast");
-            encoder.Copy(tmp, var);
-            encoder.Push();
-
-            bitCast = GetNewAlias(tmp, newType, 0, 0);
-        }
+        bitCast = ImmToVariable(var->GetImmediateValue(), newType);
     }
     else
     {

IGC/Compiler/CISACodeGen/EmitVISAPass.cpp

@@ -14460,21 +14460,26 @@ void EmitPass::emitVectorBitCast(llvm::BitCastInst* BCI)
         dstNElts = 1;
     }
 
-    uint32_t dstEltBytes = int_cast<uint32_t>((unsigned int)dstEltTy->getPrimitiveSizeInBits() / 8);
-    uint32_t srcEltBytes = int_cast<uint32_t>((unsigned int)srcEltTy->getPrimitiveSizeInBits() / 8);
     if (src->IsImmediate())
     {
-        IGC_ASSERT((dstNElts * dstEltBytes) == srcEltBytes && srcNElts == 1);
-        CVariable* tmp = m_currShader->GetNewAlias(m_destination, src->GetType(), 0, 0);
-        m_encoder->Copy(tmp, src);
+        CVariable* reg = m_currShader->GetNewVariable(
+            1,
+            src->GetType(),
+            m_encoder->GetCISADataTypeAlignment(src->GetType()),
+            true,
+            1, CName::NONE);
+
+        m_encoder->Copy(reg, src);
         m_encoder->Push();
-        return;
+
+        src = reg;
     }
 
     uint32_t width = numLanes(m_currShader->m_SIMDSize);
+    uint32_t dstEltBytes = int_cast<uint32_t>((unsigned int)dstEltTy->getPrimitiveSizeInBits() / 8);
+    uint32_t srcEltBytes = int_cast<uint32_t>((unsigned int)srcEltTy->getPrimitiveSizeInBits() / 8);
     bool srcUniform = src->IsUniform();
     bool dstUniform = m_destination->IsUniform();
-
     if (srcUniform && dstUniform &&
         (dstNElts == 2 || dstNElts == 4 || dstNElts == 8) &&
         m_destination != src &&