// See if we need to replace the return value place holder.
// Also, see if this update enables further devirtualization.
- fgWalkTreePre(&stmt->gtStmtExpr, fgUpdateInlineReturnExpressionPlaceHolder, (void*)this);
+ //
+ // Note we have both preorder and postorder callbacks here.
+ //
+ // The preorder callback is responsible for replacing GT_RET_EXPRs
+ // with the appropriate expansion (call or inline result).
+ // Replacement may introduce subtrees with GT_RET_EXPR and so
+ // we rely on the preorder to recursively process those as well.
+ //
+ // On the way back up, the postorder callback then re-examines nodes for
+ // possible further optimization, as the (now complete) GT_RET_EXPR
+ // replacement may have enabled optimizations by providing more
+ // specific types for trees or variables.
+ fgWalkTree(&stmt->gtStmtExpr, fgUpdateInlineReturnExpressionPlaceHolder, fgLateDevirtualization,
+ (void*)this);
// See if stmt is of the form GT_COMMA(call, nop)
// If yes, we can get rid of GT_COMMA.
// the inlinee return expression if the inline is successful (see
// tail end of fgInsertInlineeBlocks for the update of iciCall).
//
-// If the parent of the GT_RET_EXPR is a virtual call,
-// devirtualization is attempted. This should only succeed in the
-// successful inline case, when the inlinee's return value
-// expression provides a better type than the return type of the
-// method. Note for failed inlines, the devirtualizer can only go
-// by the return type, and any devirtualization that type enabled
-// would have already happened during importation.
-//
// If the return type is a struct type and we're on a platform
// where structs can be returned in multiple registers, ensure the
// call has a suitable parent.
Compiler::fgWalkResult Compiler::fgUpdateInlineReturnExpressionPlaceHolder(GenTree** pTree, fgWalkData* data)
{
- GenTree* tree = *pTree;
+ // All the operations here and in the corresponding postorder
+ // callback (fgLateDevirtualization) are triggered by GT_CALL or
+ // GT_RET_EXPR trees, and these (should) have the call side
+ // effect flag.
+ //
+ // So bail out for any trees that don't have this flag.
+ GenTree* tree = *pTree;
+
+ if ((tree->gtFlags & GTF_CALL) == 0)
+ {
+ return WALK_SKIP_SUBTREES;
+ }
+
Compiler* comp = data->compiler;
CORINFO_CLASS_HANDLE retClsHnd = NO_CLASS_HANDLE;
- if (tree->gtOper == GT_RET_EXPR)
+ if (tree->OperGet() == GT_RET_EXPR)
{
// We are going to copy the tree from the inlinee,
// so record the handle now.
retClsHnd = tree->gtRetExpr.gtRetClsHnd;
}
- do
- {
- // Obtained the expanded inline candidate
- GenTree* inlineCandidate = tree->gtRetExpr.gtInlineCandidate;
+ // Skip through chains of GT_RET_EXPRs (say from nested inlines)
+ // to the actual tree to use.
+ GenTree* inlineCandidate = tree->gtRetExprVal();
#ifdef DEBUG
- if (comp->verbose)
- {
- printf("\nReplacing the return expression placeholder ");
- printTreeID(tree);
- printf(" with ");
- printTreeID(inlineCandidate);
- printf("\n");
- // Dump out the old return expression placeholder it will be overwritten by the ReplaceWith below
- comp->gtDispTree(tree);
- }
+ if (comp->verbose)
+ {
+ printf("\nReplacing the return expression placeholder ");
+ printTreeID(tree);
+ printf(" with ");
+ printTreeID(inlineCandidate);
+ printf("\n");
+ // Dump out the old return expression placeholder it will be overwritten by the ReplaceWith below
+ comp->gtDispTree(tree);
+ }
#endif // DEBUG
- tree->ReplaceWith(inlineCandidate, comp);
+ tree->ReplaceWith(inlineCandidate, comp);
#ifdef DEBUG
- if (comp->verbose)
- {
- printf("\nInserting the inline return expression\n");
- comp->gtDispTree(tree);
- printf("\n");
- }
-#endif // DEBUG
- } while (tree->gtOper == GT_RET_EXPR);
-
- // Now see if this return value expression feeds the 'this'
- // object at a virtual call site.
- //
- // Note for void returns where the inline failed, the
- // GT_RET_EXPR may be top-level.
- //
- // May miss cases where there are intermediaries between call
- // and this, eg commas.
- GenTree* parentTree = data->parent;
-
- if ((parentTree != nullptr) && (parentTree->gtOper == GT_CALL))
+ if (comp->verbose)
{
- GenTreeCall* call = parentTree->AsCall();
- bool tryLateDevirt = call->IsVirtual() && (call->gtCallObjp == tree) && (call->gtCallType == CT_USER_FUNC);
-
-#ifdef DEBUG
- tryLateDevirt = tryLateDevirt && (JitConfig.JitEnableLateDevirtualization() == 1);
-#endif // DEBUG
-
- if (tryLateDevirt)
- {
-#ifdef DEBUG
- if (comp->verbose)
- {
- printf("**** Late devirt opportunity\n");
- comp->gtDispTree(call);
- }
-#endif // DEBUG
-
- CORINFO_METHOD_HANDLE method = call->gtCallMethHnd;
- unsigned methodFlags = 0;
- CORINFO_CONTEXT_HANDLE context = nullptr;
- comp->impDevirtualizeCall(call, &method, &methodFlags, &context, nullptr);
- }
+ printf("\nInserting the inline return expression\n");
+ comp->gtDispTree(tree);
+ printf("\n");
}
+#endif // DEBUG
}
// If an inline was rejected and the call returns a struct, we may
// leaving an assert in here. This can be fixed by looking ahead
// when we visit GT_ASG similar to fgAttachStructInlineeToAsg.
//
- if ((tree->gtOper == GT_ASG) && (tree->gtOp.gtOp2->gtOper == GT_COMMA))
+ if (tree->OperGet() == GT_ASG)
{
- GenTree* comma;
- for (comma = tree->gtOp.gtOp2; comma->gtOper == GT_COMMA; comma = comma->gtOp.gtOp2)
+ GenTree* value = tree->gtOp.gtOp2;
+
+ if (value->OperGet() == GT_COMMA)
{
- // empty
- }
+ GenTree* effectiveValue = value->gtEffectiveVal(/*commaOnly*/ true);
- noway_assert(!varTypeIsStruct(comma) || comma->gtOper != GT_RET_EXPR ||
- !comp->IsMultiRegReturnedType(comma->gtRetExpr.gtRetClsHnd));
+ noway_assert(!varTypeIsStruct(effectiveValue) || (effectiveValue->OperGet() != GT_RET_EXPR) ||
+ !comp->IsMultiRegReturnedType(effectiveValue->gtRetExpr.gtRetClsHnd));
+ }
}
#endif // defined(DEBUG)
return WALK_CONTINUE;
}
+//------------------------------------------------------------------------
+// fgLateDevirtualization: re-examine calls after inlining to see if we
+// can do more devirtualization
+//
+// Arguments:
+// pTree -- pointer to tree to examine for updates
+// data -- context data for the tree walk
+//
+// Returns:
+// fgWalkResult indicating the walk should continue; that
+// is we wish to fully explore the tree.
+//
+// Notes:
+// We used to check this opportunistically in the preorder callback for
+// calls where the `obj` was fed by a return, but we now re-examine
+// all calls.
+//
+// Late devirtualization (and eventually, perhaps, other type-driven
+// opts like cast optimization) can happen now because inlining or other
+// optimizations may have provided more accurate types than we saw when
+// first importing the trees.
+//
+// It would be nice to screen candidate sites based on the likelihood
+// that something has changed. Otherwise we'll waste some time retrying
+// an optimization that will just fail again.
+
+Compiler::fgWalkResult Compiler::fgLateDevirtualization(GenTree** pTree, fgWalkData* data)
+{
+ GenTree* tree = *pTree;
+ GenTree* parent = data->parent;
+ Compiler* comp = data->compiler;
+
+ // In some (rare) cases the parent node of tree will be smashed to a NOP during
+ // the preorder by fgAttachStructToInlineeArg.
+ //
+ // jit\Methodical\VT\callconv\_il_reljumper3 for x64 linux
+ //
+ // If so, just bail out here.
+ if ((parent != nullptr) && parent->OperGet() == GT_NOP)
+ {
+ assert(tree == nullptr);
+ return WALK_CONTINUE;
+ }
+
+ if (tree->OperGet() == GT_CALL)
+ {
+ GenTreeCall* call = tree->AsCall();
+ bool tryLateDevirt = call->IsVirtual() && (call->gtCallType == CT_USER_FUNC);
+
+#ifdef DEBUG
+ tryLateDevirt = tryLateDevirt && (JitConfig.JitEnableLateDevirtualization() == 1);
+#endif // DEBUG
+
+ if (tryLateDevirt)
+ {
+#ifdef DEBUG
+ if (comp->verbose)
+ {
+ printf("**** Late devirt opportunity\n");
+ comp->gtDispTree(call);
+ }
+#endif // DEBUG
+
+ CORINFO_METHOD_HANDLE method = call->gtCallMethHnd;
+ unsigned methodFlags = 0;
+ CORINFO_CONTEXT_HANDLE context = nullptr;
+ comp->impDevirtualizeCall(call, &method, &methodFlags, &context, nullptr);
+ }
+ }
+
+ return WALK_CONTINUE;
+}
+
#ifdef DEBUG
/*****************************************************************************
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