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.

Change-Id: I2ca811e385e91f682976b5ba209df1e598513e84

Author: jgu222

IGC/Compiler/CISACodeGen/CShader.cpp

@@ -857,9 +857,32 @@ 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, which means
+    // one element size is the same as or multiple of the other (if they
+    // are vectors with different number of elements).
+    IGC_ASSERT(   (newEltSz >= eltSz && (newEltSz % eltSz) == 0)
+               || (newEltSz < eltSz && (eltSz% newEltSz) == 0));
     if (var->IsImmediate())
     {
-        bitCast = ImmToVariable(var->GetImmediateValue(), newType);
+        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);
+        }
     }
     else
     {

IGC/Compiler/CISACodeGen/EmitVISAPass.cpp

@@ -3020,7 +3020,7 @@ void EmitPass::Mul64(CVariable* dst, CVariable* src[2], SIMDMode simdMode, bool
     CVariable* srcLo[2], * srcHi[2];
     for (int i = 0; i < 2; ++i)
     {
-        CVariable* srcAsUD = m_currShader->BitCast(src[i], ISA_TYPE_UD);
+        CVariable* srcAsUD;
         if (src[i]->IsUniform())
         {
             if (src[i]->IsImmediate())
@@ -3030,12 +3030,14 @@ void EmitPass::Mul64(CVariable* dst, CVariable* src[2], SIMDMode simdMode, bool
             }
             else
             {
+                srcAsUD = m_currShader->BitCast(src[i], ISA_TYPE_UD);
                 srcLo[i] = m_currShader->GetNewAlias(srcAsUD, ISA_TYPE_UD, 0, 1);
                 srcHi[i] = m_currShader->GetNewAlias(srcAsUD, hiType, SIZE_DWORD, 1);
             }
         }
         else
         {
+            srcAsUD = m_currShader->BitCast(src[i], ISA_TYPE_UD);
             //TODO: Would it be better for these two to be consecutive?
             srcLo[i] = m_currShader->GetNewVariable(
                 src[i]->GetNumberElement(),