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Skip FP registers processing if method don't have floating points use #85744

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merged 4 commits into from
May 6, 2023
Merged

Skip FP registers processing if method don't have floating points use #85744

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fe09c7f
skip processing floating point registers if method doesn't have one
kunalspathak May 4, 2023
8a7d379
Rename to needNonIntegerRegisters
kunalspathak May 4, 2023
e295312
Merge remote-tracking branch 'origin/main' into lsra-throughput
kunalspathak May 4, 2023
de985d6
jit format
kunalspathak May 5, 2023
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4 changes: 2 additions & 2 deletions src/coreclr/jit/importer.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -66,11 +66,11 @@ void Compiler::impPushOnStack(GenTree* tree, typeInfo ti)
verCurrentState.esStack[verCurrentState.esStackDepth].seTypeInfo = ti;
verCurrentState.esStack[verCurrentState.esStackDepth++].val = tree;

if ((tree->gtType == TYP_LONG) && (compLongUsed == false))
if (tree->gtType == TYP_LONG)
{
compLongUsed = true;
}
else if (((tree->gtType == TYP_FLOAT) || (tree->gtType == TYP_DOUBLE)) && (compFloatingPointUsed == false))
else if ((tree->gtType == TYP_FLOAT) || (tree->gtType == TYP_DOUBLE))
{
compFloatingPointUsed = true;
}
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8 changes: 6 additions & 2 deletions src/coreclr/jit/lsra.cpp
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Expand Up @@ -418,6 +418,8 @@ void LinearScan::updateRegsFreeBusyState(RefPosition& refPosition,

regMaskTP LinearScan::internalFloatRegCandidates()
{
needNonIntegerRegisters = true;

if (compiler->compFloatingPointUsed)
{
return availableFloatRegs;
Expand Down Expand Up @@ -686,13 +688,15 @@ LinearScan::LinearScan(Compiler* theCompiler)
, refPositions(theCompiler->getAllocator(CMK_LSRA_RefPosition))
, listNodePool(theCompiler)
{
availableRegCount = ACTUAL_REG_COUNT;
needNonIntegerRegisters = false;

#if defined(TARGET_XARCH)
availableRegCount = ACTUAL_REG_COUNT;

#if defined(TARGET_AMD64)
rbmAllFloat = compiler->rbmAllFloat;
rbmFltCalleeTrash = compiler->rbmFltCalleeTrash;
#endif
#endif // TARGET_AMD64

if (!compiler->canUseEvexEncoding())
{
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4 changes: 3 additions & 1 deletion src/coreclr/jit/lsra.h
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Expand Up @@ -733,6 +733,7 @@ class LinearScan : public LinearScanInterface
unsigned int currentSpill[TYP_COUNT];
bool needFloatTmpForFPCall;
bool needDoubleTmpForFPCall;
bool needNonIntegerRegisters;

#ifdef DEBUG
private:
Expand Down Expand Up @@ -2041,13 +2042,14 @@ class LinearScan : public LinearScanInterface
}
#endif // TARGET_AMD64

#endif // TARGET_XARCH

unsigned availableRegCount;

unsigned get_AVAILABLE_REG_COUNT() const
{
return this->availableRegCount;
}
#endif // TARGET_XARCH

//------------------------------------------------------------------------
// calleeSaveRegs: Get the set of callee-save registers of the given RegisterType
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14 changes: 14 additions & 0 deletions src/coreclr/jit/lsrabuild.cpp
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Expand Up @@ -1940,6 +1940,14 @@ void LinearScan::buildPhysRegRecords()
RegRecord* curr = &physRegs[reg];
curr->regOrder = (unsigned char)i;
}

// TODO-CQ: We build physRegRecords before building intervals
// and refpositions. During building intervals/refposition, we
// would know if there are floating points used. If we can know
// that information before we build intervals, we can skip
// initializing the floating registers.
// For that `compFloatingPointUsed` should be set accurately
// before invoking allocator.
Comment on lines +1949 to +1950
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I think this bit in particular is a bit difficult as we need to pre-emptively set compFloatingPointUsed for any SIMD code. But that can't really account for dead code elimination or other factors that might later remove or transforms the nodes to no longer need it.

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@tannergooding tannergooding May 5, 2023 •
edited
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Would it instead be possible to have regMaskTP LinearScan::internalFloatRegCandidates() lazily do the below, or is there other factors that require it?

That is, have it do something like:

regMaskTP LinearScan::internalFloatRegCandidates()
{
    if (!needNonIntegerRegisters)
    {
        // lazily initialize fpreg state here

        for (unsigned int i = 0; i < lsraRegOrderFltSize; i++)
        {
            regNumber  reg  = lsraRegOrderFlt[i];
            RegRecord* curr = &physRegs[reg];
            curr->regOrder  = (unsigned char)i;
        }

        needNonIntegerRegisters = true;
    }

    if (compiler->compFloatingPointUsed)
    {
        return availableFloatRegs;
    }
    else
    {
        return RBM_FLT_CALLEE_TRASH;
    }
}

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Unfortunately we need the physRegRecord early right after identifying candidates.

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@kunalspathak kunalspathak May 5, 2023 •
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But that can't really account for dead code elimination or other factors that might later remove or transforms the nodes to no longer need it.

True, but this is the best we can do I suppose, unless you are proposing to just start from scratch in LSRA and set it to true during BuildNode() if tree->GetType() != TYP_INT.

Edit: Doing the check in BuildNode() might prove costly though because we will be doing that for every single GenTree* node and not sure how many cases we will optimize for the scenarios where we didn't account for dead code elimination.

for (unsigned int i = 0; i < lsraRegOrderFltSize; i++)
{
regNumber reg = lsraRegOrderFlt[i];
Expand Down Expand Up @@ -2727,6 +2735,12 @@ void LinearScan::buildIntervals()
RefPosition* pos = newRefPosition((Interval*)nullptr, currentLoc, RefTypeBB, nullptr, RBM_NONE);
}

needNonIntegerRegisters |= compiler->compFloatingPointUsed;
if (!needNonIntegerRegisters)
{
availableRegCount = REG_INT_COUNT;
}

#ifdef DEBUG
// Make sure we don't have any blocks that were not visited
for (BasicBlock* const block : compiler->Blocks())
Expand Down
5 changes: 0 additions & 5 deletions src/coreclr/jit/target.h
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Expand Up @@ -196,12 +196,7 @@ enum _regMask_enum : unsigned
#error Unsupported target architecture
#endif

#if defined(TARGET_XARCH)
// AVAILABLE_REG_COUNT is defined to be dynamic, based on whether AVX-512 high registers are available.
#define AVAILABLE_REG_COUNT get_AVAILABLE_REG_COUNT()
#else
#define AVAILABLE_REG_COUNT ACTUAL_REG_COUNT
#endif

/*****************************************************************************/

Expand Down