Copy propagation tweaking (#64378)

* Relax the type check

The type check is too conservative: it prevents partial
definitions from being used in propagation:
```
LCL_FLD V00/1 [X] = { ... }; // Pushed on the stack as a def.

USE LCL_VAR V01 // Has the same VN as V00/1, but the type
                // check prevented it from being replaced.
```
This new version is conservative too, but will do for now
as we don't propagate on (most) partial uses.

Another reason for this change is that in my upcoming refactoring
of copy propagation (that will bring another 0.5% in TP gains), we
will no longer have the "defNode" available.

* Do not propagate shadowed "this"

Ordinarily, shadowed parameters would not be used for
propagation anyway, because of the liveness check, but
"this" bypasses that checks, and so was used, which is
presumably not what we want.

Regardless of that, it is also not profitable to propagate
"this" in such a situation as it extends its live range
and makes the RA unhappy.

* NO_SHADOW_COPY -> BAD_VAR_NUM

Author: SingleAccretion

src/coreclr/jit/compiler.h

@@ -10893,7 +10893,7 @@ XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
     struct ShadowParamVarInfo
     {
         FixedBitVect* assignGroup; // the closure set of variables whose values depend on each other
-        unsigned      shadowCopy;  // Lcl var num, valid only if not set to NO_SHADOW_COPY
+        unsigned      shadowCopy;  // Lcl var num, if not valid set to BAD_VAR_NUM
 
         static bool mayNeedShadowCopy(LclVarDsc* varDsc)
         {

src/coreclr/jit/copyprop.cpp

@@ -161,7 +161,7 @@ void Compiler::optCopyProp(Statement*               stmt,
         }
 
         if ((gsShadowVarInfo != nullptr) && newLclVarDsc->lvIsParam &&
-            (gsShadowVarInfo[newLclNum].shadowCopy == lclNum))
+            (gsShadowVarInfo[newLclNum].shadowCopy != BAD_VAR_NUM))
         {
             continue;
         }
@@ -172,11 +172,6 @@ void Compiler::optCopyProp(Statement*               stmt,
             continue;
         }
 
-        if (newLclDefNode->TypeGet() != tree->TypeGet())
-        {
-            continue;
-        }
-
         ValueNum lclDefVN = varDsc->GetPerSsaData(tree->GetSsaNum())->m_vnPair.GetConservative();
         if (newLclDefVN != lclDefVN)
         {
@@ -226,6 +221,17 @@ void Compiler::optCopyProp(Statement*               stmt,
             continue;
         }
 
+        var_types newLclType = newLclVarDsc->TypeGet();
+        if (!newLclVarDsc->lvNormalizeOnLoad())
+        {
+            newLclType = genActualType(newLclType);
+        }
+
+        if (newLclType != tree->TypeGet())
+        {
+            continue;
+        }
+
 #ifdef DEBUG
         if (verbose)
         {

src/coreclr/jit/gschecks.cpp

@@ -32,8 +32,6 @@ void Compiler::gsGSChecksInitCookie()
     info.compCompHnd->getGSCookie(&gsGlobalSecurityCookieVal, &gsGlobalSecurityCookieAddr);
 }
 
-const unsigned NO_SHADOW_COPY = UINT_MAX;
-
 /*****************************************************************************
  * gsCopyShadowParams
  * The current function has an unsafe buffer on the stack.  Search for vulnerable
@@ -368,7 +366,7 @@ void Compiler::gsParamsToShadows()
     for (UINT lclNum = 0; lclNum < lvaOldCount; lclNum++)
     {
         LclVarDsc* varDsc                  = lvaGetDesc(lclNum);
-        gsShadowVarInfo[lclNum].shadowCopy = NO_SHADOW_COPY;
+        gsShadowVarInfo[lclNum].shadowCopy = BAD_VAR_NUM;
 
         // Only care about params whose values are on the stack
         if (!ShadowParamVarInfo::mayNeedShadowCopy(varDsc))
@@ -452,7 +450,7 @@ void Compiler::gsParamsToShadows()
             unsigned int lclNum       = tree->AsLclVarCommon()->GetLclNum();
             unsigned int shadowLclNum = m_compiler->gsShadowVarInfo[lclNum].shadowCopy;
 
-            if (shadowLclNum != NO_SHADOW_COPY)
+            if (shadowLclNum != BAD_VAR_NUM)
             {
                 LclVarDsc* varDsc = m_compiler->lvaGetDesc(lclNum);
                 assert(ShadowParamVarInfo::mayNeedShadowCopy(varDsc));
@@ -492,7 +490,7 @@ void Compiler::gsParamsToShadows()
         const LclVarDsc* varDsc = lvaGetDesc(lclNum);
 
         const unsigned shadowVarNum = gsShadowVarInfo[lclNum].shadowCopy;
-        if (shadowVarNum == NO_SHADOW_COPY)
+        if (shadowVarNum == BAD_VAR_NUM)
         {
             continue;
         }
@@ -544,7 +542,7 @@ void Compiler::gsParamsToShadows()
                 const LclVarDsc* varDsc = lvaGetDesc(lclNum);
 
                 const unsigned shadowVarNum = gsShadowVarInfo[lclNum].shadowCopy;
-                if (shadowVarNum == NO_SHADOW_COPY)
+                if (shadowVarNum == BAD_VAR_NUM)
                 {
                     continue;
                 }