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JIT: update tail call IR validity checks #94130

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merged 2 commits into from
Oct 30, 2023
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JIT: update tail call IR validity checks #94130

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f8e2f0a
JIT: rework tail call IR validity checks
AndyAyersMS Oct 28, 2023
8f02902
revise to just remove fgCheckStmtAfterTailCall
AndyAyersMS Oct 28, 2023
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1 change: 0 additions & 1 deletion src/coreclr/jit/compiler.h
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Original file line number Diff line number Diff line change
Expand Up @@ -5979,7 +5979,6 @@ class Compiler
bool fgCallArgWillPointIntoLocalFrame(GenTreeCall* call, CallArg& arg);

#endif
bool fgCheckStmtAfterTailCall();
GenTree* fgMorphTailCallViaHelpers(GenTreeCall* call, CORINFO_TAILCALL_HELPERS& help);
bool fgCanTailCallViaJitHelper(GenTreeCall* call);
void fgMorphTailCallViaJitHelper(GenTreeCall* call);
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108 changes: 0 additions & 108 deletions src/coreclr/jit/morph.cpp
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Expand Up @@ -5894,12 +5894,6 @@ GenTree* Compiler::fgMorphPotentialTailCall(GenTreeCall* call)
}
}

if (!fgCheckStmtAfterTailCall())
{
failTailCall("Unexpected statements after the tail call");
return nullptr;
}

const char* failReason = nullptr;
bool canFastTailCall = fgCanFastTailCall(call, &failReason);

Expand Down Expand Up @@ -15367,108 +15361,6 @@ void Compiler::fgMarkDemotedImplicitByRefArgs()
#endif // FEATURE_IMPLICIT_BYREFS
}

//------------------------------------------------------------------------
// fgCheckStmtAfterTailCall: check that statements after the tail call stmt
// candidate are in one of expected forms, that are desctibed below.
//
// Return Value:
// 'true' if stmts are in the expected form, else 'false'.
//
bool Compiler::fgCheckStmtAfterTailCall()
{

// For void calls, we would have created a GT_CALL in the stmt list.
// For non-void calls, we would have created a GT_RETURN(GT_CAST(GT_CALL)).
// For calls returning structs, we would have a void call, followed by a void return.
// For debuggable code, it would be an assignment of the call to a temp
// We want to get rid of any of this extra trees, and just leave
// the call.
Statement* callStmt = fgMorphStmt;

Statement* nextMorphStmt = callStmt->GetNextStmt();

// Check that the rest stmts in the block are in one of the following pattern:
// 1) ret(void)
// 2) ret(cast*(callResultLclVar))
// 3) lclVar = callResultLclVar, the actual ret(lclVar) in another block
// 4) nop
if (nextMorphStmt != nullptr)
{
GenTree* callExpr = callStmt->GetRootNode();
if (!callExpr->OperIs(GT_STORE_LCL_VAR))
{
// The next stmt can be GT_RETURN(TYP_VOID) or GT_RETURN(lclVar),
// where lclVar was return buffer in the call for structs or simd.
Statement* retStmt = nextMorphStmt;
GenTree* retExpr = retStmt->GetRootNode();
noway_assert(retExpr->gtOper == GT_RETURN);

nextMorphStmt = retStmt->GetNextStmt();
}
else
{
noway_assert(callExpr->OperIs(GT_STORE_LCL_VAR));
unsigned callResultLclNumber = callExpr->AsLclVar()->GetLclNum();

#if FEATURE_TAILCALL_OPT_SHARED_RETURN

// We can have a chain of assignments from the call result to
// various inline return spill temps. These are ok as long
// as the last one ultimately provides the return value or is ignored.
//
// And if we're returning a small type we may see a cast
// on the source side.
while ((nextMorphStmt != nullptr) && (nextMorphStmt->GetRootNode()->OperIs(GT_STORE_LCL_VAR, GT_NOP)))
{
if (nextMorphStmt->GetRootNode()->OperIs(GT_NOP))
{
nextMorphStmt = nextMorphStmt->GetNextStmt();
continue;
}
Statement* moveStmt = nextMorphStmt;
GenTree* moveExpr = nextMorphStmt->GetRootNode();

// Tunnel through any casts on the source side.
GenTree* moveSource = moveExpr->AsLclVar()->Data();
while (moveSource->OperIs(GT_CAST))
{
noway_assert(!moveSource->gtOverflow());
moveSource = moveSource->gtGetOp1();
}
noway_assert(moveSource->OperIsLocal());

// Verify we're just passing the value from one local to another
// along the chain.
const unsigned srcLclNum = moveSource->AsLclVarCommon()->GetLclNum();
noway_assert(srcLclNum == callResultLclNumber);
const unsigned dstLclNum = moveExpr->AsLclVar()->GetLclNum();
callResultLclNumber = dstLclNum;

nextMorphStmt = moveStmt->GetNextStmt();
}
if (nextMorphStmt != nullptr)
#endif
{
Statement* retStmt = nextMorphStmt;
GenTree* retExpr = nextMorphStmt->GetRootNode();
noway_assert(retExpr->gtOper == GT_RETURN);

GenTree* treeWithLcl = retExpr->gtGetOp1();
while (treeWithLcl->gtOper == GT_CAST)
{
noway_assert(!treeWithLcl->gtOverflow());
treeWithLcl = treeWithLcl->gtGetOp1();
}

noway_assert(callResultLclNumber == treeWithLcl->AsLclVarCommon()->GetLclNum());

nextMorphStmt = retStmt->GetNextStmt();
}
}
}
return nextMorphStmt == nullptr;
}

//------------------------------------------------------------------------
// fgCanTailCallViaJitHelper: check whether we can use the faster tailcall
// JIT helper on x86.
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