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Liveness fix for struct enreg. #51851

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Merged
merged 3 commits into from
Apr 28, 2021
Merged

Liveness fix for struct enreg. #51851

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ba46901
Improve mustInit for structs.
Apr 26, 2021
5284943
fix linux
Apr 27, 2021
a9738ed
review response.
Apr 28, 2021
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58 changes: 43 additions & 15 deletions src/coreclr/jit/codegencommon.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -4747,15 +4747,21 @@ void CodeGen::genCheckUseBlockInit()
continue;
}

if (varDsc->lvIsTemp && !varDsc->HasGCPtr())
const bool isTemp = varDsc->lvIsTemp;
const bool hasGCPtr = varDsc->HasGCPtr();
const bool isTracked = varDsc->lvTracked;
const bool isStruct = varTypeIsStruct(varDsc);
const bool compInitMem = compiler->info.compInitMem;

if (isTemp && !hasGCPtr)
{
varDsc->lvMustInit = 0;
continue;
}

if (compiler->info.compInitMem || varDsc->HasGCPtr() || varDsc->lvMustInit)
if (compInitMem || hasGCPtr || varDsc->lvMustInit)
{
if (varDsc->lvTracked)
if (isTracked)
{
/* For uninitialized use of tracked variables, the liveness
* will bubble to the top (compiler->fgFirstBB) in fgInterBlockLocalVarLiveness()
Expand Down Expand Up @@ -4794,20 +4800,42 @@ void CodeGen::genCheckUseBlockInit()
}
}

/* With compInitMem, all untracked vars will have to be init'ed */
/* VSW 102460 - Do not force initialization of compiler generated temps,
unless they are untracked GC type or structs that contain GC pointers */
CLANG_FORMAT_COMMENT_ANCHOR;

if ((!varDsc->lvTracked || (varDsc->lvType == TYP_STRUCT)) && varDsc->lvOnFrame)
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@erozenfeld erozenfeld Apr 27, 2021 •
edited
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The new logic doesn't take into account varDsc->lvOnFrame. Is that intentional?

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Good question, if I add an assert like if (mustInitThisVar) assert(varDsc->lvOnFrame); it won't fail (x64 spmi) but it is a current implicit contract so we probably should not rely on it.

if (hasGCPtr && !isTracked) -> not tracked means not in register -> lvOnFrame == true
else if (hasGCPtr && isStruct) -> do not enregister structs, with https://github.com/dotnet/runtime/pull/51850/checks?check_run_id=2447290001 won't enregister structs with GC pointers -> lvOnFrame == true
if (!isTracked)  -> not tracked means not in register -> lvOnFrame == true

I will return the condition, thank you.

if (varDsc->lvOnFrame)
{

varDsc->lvMustInit = true;

if (!counted)
bool mustInitThisVar = false;
if (hasGCPtr && !isTracked)
{
JITDUMP("must init V%02u because it has a GC ref\n", varNum);
mustInitThisVar = true;
}
else if (hasGCPtr && isStruct)
{
// TODO-1stClassStructs: support precise liveness reporting for such structs.
JITDUMP("must init a tracked V%02u because it a struct with a GC ref\n", varNum);
mustInitThisVar = true;
}
else
{
initStkLclCnt += roundUp(compiler->lvaLclSize(varNum), TARGET_POINTER_SIZE) / sizeof(int);
counted = true;
// We are done with tracked or GC vars, now look at untracked vars without GC refs.
if (!isTracked)
{
assert(!hasGCPtr && !isTemp);
if (compInitMem)
{
JITDUMP("must init V%02u because compInitMem is set and it is not a temp\n", varNum);
mustInitThisVar = true;
}
}
}
if (mustInitThisVar)
{
varDsc->lvMustInit = true;

if (!counted)
{
initStkLclCnt += roundUp(compiler->lvaLclSize(varNum), TARGET_POINTER_SIZE) / sizeof(int);
counted = true;
}
}
}
}
Expand Down
2 changes: 1 addition & 1 deletion src/coreclr/jit/compiler.h
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Expand Up @@ -971,7 +971,7 @@ class LclVarDsc
var_types lvaArgType();

// Returns true if this variable contains GC pointers (including being a GC pointer itself).
bool HasGCPtr()
bool HasGCPtr() const
{
return varTypeIsGC(lvType) || ((lvType == TYP_STRUCT) && m_layout->HasGCPtr());
}
Expand Down
22 changes: 20 additions & 2 deletions src/coreclr/jit/lower.cpp
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Expand Up @@ -5915,17 +5915,35 @@ void Lowering::CheckNode(Compiler* compiler, GenTree* node)
{
unsigned lclNum = node->AsLclVarCommon()->GetLclNum();
LclVarDsc* lclVar = &compiler->lvaTable[lclNum];
#ifdef DEBUG
if (node->TypeIs(TYP_SIMD12))
{
assert(compiler->lvaIsFieldOfDependentlyPromotedStruct(lclVar) || (lclVar->lvSize() == 12));
}
#endif // DEBUG
}
break;
#endif // TARGET_64BIT
#endif // SIMD

case GT_LCL_VAR_ADDR:
case GT_LCL_FLD_ADDR:
{
const GenTreeLclVarCommon* lclVarAddr = node->AsLclVarCommon();
const LclVarDsc* varDsc = compiler->lvaGetDesc(lclVarAddr);
if (((lclVarAddr->gtFlags & GTF_VAR_DEF) != 0) && varDsc->HasGCPtr())
{
// Emitter does not correctly handle live updates for LCL_VAR_ADDR
// when they are not contained, for example, `STOREIND byref(GT_LCL_VAR_ADDR not-contained)`
// would generate:
// add r1, sp, 48 // r1 contains address of a lclVar V01.
// str r0, [r1] // a gc ref becomes live in V01, but emitter would not report it.
// Make sure that we use uncontained address nodes only for variables
// that will be marked as mustInit and will be alive throughout the whole block even when tracked.
assert(lclVarAddr->isContained() || !varDsc->lvTracked || varTypeIsStruct(varDsc));
// TODO: support this assert for uses, see https://github.com/dotnet/runtime/issues/51900.
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#51900

}
break;
}

default:
break;
}
Expand Down
3 changes: 2 additions & 1 deletion src/coreclr/jit/optimizer.cpp
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Expand Up @@ -9760,7 +9760,8 @@ void Compiler::optRemoveRedundantZeroInits()
if (BitVecOps::IsMember(&bitVecTraits, zeroInitLocals, lclNum) ||
(lclDsc->lvIsStructField &&
BitVecOps::IsMember(&bitVecTraits, zeroInitLocals, lclDsc->lvParentLcl)) ||
(!lclDsc->lvTracked && !fgVarNeedsExplicitZeroInit(lclNum, bbInALoop, bbIsReturn)))
((!lclDsc->lvTracked || !isEntire) &&
!fgVarNeedsExplicitZeroInit(lclNum, bbInALoop, bbIsReturn)))
{
// We are guaranteed to have a zero initialization in the prolog or a
// dominating explicit zero initialization and the local hasn't been redefined
Expand Down