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-rw-r--r--src/jit/liveness.cpp87
1 files changed, 59 insertions, 28 deletions
diff --git a/src/jit/liveness.cpp b/src/jit/liveness.cpp
index 2ac59245a1..dddb45fa28 100644
--- a/src/jit/liveness.cpp
+++ b/src/jit/liveness.cpp
@@ -700,14 +700,14 @@ void Compiler::fgPerBlockLocalVarLiveness()
}
+ // If this is an assignment to local var with no SIDE EFFECTS,
+ // set lhsNode so that genMarkUseDef will flag potential
+ // x=f(x) expressions as GTF_VAR_USEDEF.
+ // Reset the flag before recomputing it - it may have been set before,
+ // but subsequent optimizations could have removed the rhs reference.
+ lhsNode->gtFlags &= ~GTF_VAR_USEDEF;
if ((rhsNode->gtFlags & GTF_SIDE_EFFECT) == 0)
{
- // Assignment to local var with no SIDE EFFECTS.
- // Set lhsNode so that genMarkUseDef will flag potential
- // x=f(x) expressions as GTF_VAR_USEDEF.
- // Reset the flag before recomputing it - it may have been set before,
- // but subsequent optimizations could have removed the rhs reference.
- lhsNode->gtFlags &= ~GTF_VAR_USEDEF;
noway_assert(lhsNode->gtFlags & GTF_VAR_DEF);
}
else
@@ -1631,7 +1631,8 @@ VARSET_VALRET_TP Compiler::fgUpdateLiveSet(VARSET_VALARG_TP liveSet,
VARSET_VALRET_TP Compiler::fgComputeLife(VARSET_VALARG_TP lifeArg,
GenTreePtr startNode,
GenTreePtr endNode,
- VARSET_VALARG_TP volatileVars
+ VARSET_VALARG_TP volatileVars,
+ bool* pStmtInfoDirty
DEBUGARG(bool* treeModf))
{
GenTreePtr tree;
@@ -2029,7 +2030,7 @@ SKIP_QMARK:
that will be used (e.g. while (i++) or a GT_COMMA) */
bool doAgain = false;
- if (fgRemoveDeadStore(&tree, varDsc, life, &doAgain DEBUGARG(treeModf)))
+ if (fgRemoveDeadStore(&tree, varDsc, life, &doAgain, pStmtInfoDirty DEBUGARG(treeModf)))
break;
if (doAgain)
@@ -2188,7 +2189,7 @@ SKIP_QMARK:
(nextColonExit == gtQMark->gtOp.gtOp1 ||
nextColonExit == gtQMark->gtOp.gtOp2));
- VarSetOps::AssignNoCopy(this, life, fgComputeLife(life, tree, nextColonExit, volatileVars DEBUGARG(treeModf)));
+ VarSetOps::AssignNoCopy(this, life, fgComputeLife(life, tree, nextColonExit, volatileVars, pStmtInfoDirty DEBUGARG(treeModf)));
/* Continue with exit node (the last node in the enclosing colon branch) */
@@ -2228,14 +2229,15 @@ SKIP_QMARK:
// fgRemoveDeadStore - remove a store to a local which has no exposed uses.
//
-// pTree - GenTree** to an assign node (pre-rationalize) or store-form local (post-rationalize)
-// varDsc - var that is being stored to
-// life - current live tracked vars (maintained as we walk backwards)
-// doAgain - out parameter, true if we should restart the statement
+// pTree - GenTree** to an assign node (pre-rationalize) or store-form local (post-rationalize)
+// varDsc - var that is being stored to
+// life - current live tracked vars (maintained as we walk backwards)
+// doAgain - out parameter, true if we should restart the statement
+// pStmtInfoDirty - should defer the cost computation to the point after the reverse walk is completed?
//
// Returns: true if we should skip the rest of the statement, false if we should continue
-bool Compiler::fgRemoveDeadStore(GenTree** pTree, LclVarDsc* varDsc, VARSET_TP life, bool *doAgain DEBUGARG(bool* treeModf))
+bool Compiler::fgRemoveDeadStore(GenTree** pTree, LclVarDsc* varDsc, VARSET_TP life, bool *doAgain, bool* pStmtInfoDirty DEBUGARG(bool* treeModf))
{
GenTree* asgNode;
GenTree* rhsNode;
@@ -2355,23 +2357,28 @@ bool Compiler::fgRemoveDeadStore(GenTree** pTree, LclVarDsc* varDsc, VARSET_TP l
*treeModf = true;
#endif // DEBUG
- /* Update ordering, costs, FP levels, etc. */
- gtSetStmtInfo(compCurStmt);
+ // Make sure no previous cousin subtree rooted at a common ancestor has
+ // asked to defer the recomputation of costs.
+ if (!*pStmtInfoDirty)
+ {
+ /* Update ordering, costs, FP levels, etc. */
+ gtSetStmtInfo(compCurStmt);
- /* Re-link the nodes for this statement */
- fgSetStmtSeq(compCurStmt);
+ /* Re-link the nodes for this statement */
+ fgSetStmtSeq(compCurStmt);
- // Start from the old assign node, as we have changed the order of its operands.
- // No need to update liveness, as nothing has changed (the target of the asgNode
- // either goes dead here, in which case the whole expression is now dead, or it
- // was already live).
+ // Start from the old assign node, as we have changed the order of its operands.
+ // No need to update liveness, as nothing has changed (the target of the asgNode
+ // either goes dead here, in which case the whole expression is now dead, or it
+ // was already live).
- // TODO-Throughput: Redo this so that the graph is modified BEFORE traversing it!
- // We can determine this case when we first see the asgNode
+ // TODO-Throughput: Redo this so that the graph is modified BEFORE traversing it!
+ // We can determine this case when we first see the asgNode
- *pTree = asgNode;
+ *pTree = asgNode;
- *doAgain = true;
+ *doAgain = true;
+ }
return false;
}
@@ -2443,6 +2450,10 @@ bool Compiler::fgRemoveDeadStore(GenTree** pTree, LclVarDsc* varDsc, VARSET_TP l
/* Re-link the nodes for this statement */
fgSetStmtSeq(compCurStmt);
+ // Since the whole statement gets replaced it is safe to
+ // re-thread and update order. No need to compute costs again.
+ *pStmtInfoDirty = false;
+
/* Compute the live set for the new statement */
*doAgain = true;
return false;
@@ -2467,6 +2478,13 @@ bool Compiler::fgRemoveDeadStore(GenTree** pTree, LclVarDsc* varDsc, VARSET_TP l
goto EXTRACT_SIDE_EFFECTS;
}
+ // If there is an embedded statement this could be tricky because we need to
+ // walk them next, and we have already skipped over them because they were
+ // not top level (but will be if we delete the top level statement)
+ if (compCurStmt->gtStmt.gtNextStmt &&
+ !compCurStmt->gtStmt.gtNextStmt->gtStmtIsTopLevel())
+ return false;
+
/* No side effects - remove the whole statement from the block->bbTreeList */
fgRemoveStmt(compCurBB, compCurStmt);
@@ -2589,7 +2607,13 @@ bool Compiler::fgRemoveDeadStore(GenTree** pTree, LclVarDsc* varDsc, VARSET_TP l
if (!compRationalIRForm)
{
- gtSetStmtInfo(compCurStmt);
+ // Do not update costs by calling gtSetStmtInfo. fgSetStmtSeq modifies
+ // the tree threading based on the new costs. Removing nodes could
+ // cause a subtree to get evaluated first (earlier second) during the
+ // liveness walk. Instead just set a flag that costs are dirty and
+ // caller has to call gtSetStmtInfo.
+ *pStmtInfoDirty = true;
+
fgSetStmtSeq(compCurStmt);
}
@@ -2817,8 +2841,15 @@ void Compiler::fgInterBlockLocalVarLiveness()
continue;
/* Compute the liveness for each tree node in the statement */
+ bool stmtInfoDirty = false;
- VarSetOps::AssignNoCopy(this, life, fgComputeLife(life, compCurStmt->gtStmt.gtStmtExpr, NULL, volatileVars DEBUGARG(&treeModf)));
+ VarSetOps::AssignNoCopy(this, life, fgComputeLife(life, compCurStmt->gtStmt.gtStmtExpr, NULL, volatileVars, &stmtInfoDirty DEBUGARG(&treeModf)));
+
+ if (stmtInfoDirty)
+ {
+ gtSetStmtInfo(compCurStmt);
+ fgSetStmtSeq(compCurStmt);
+ }
#ifdef DEBUG
if (verbose && treeModf)
generated by cgit v1.2.3 (git 2.25.1) at 2024-05-29 01:13:01 +0000