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[release/8.0] Check if loop body occured before loopTop and if so unmark alignment #91918

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merged 4 commits into from
Sep 18, 2023
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[release/8.0] Check if loop body occured before loopTop and if so unmark alignment #91918

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2264fb6
Check if loop body occured before loopTop"
kunalspathak Sep 10, 2023
34f74f5
Merge remote-tracking branch 'origin/release/8.0' into pr-91854
kunalspathak Sep 12, 2023
db15d80
Check if bbNatLoopNum is not NOT_IN_LOOP
kunalspathak Sep 15, 2023
798f438
review feedback
kunalspathak Sep 15, 2023
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34 changes: 31 additions & 3 deletions src/coreclr/jit/compiler.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -5282,6 +5282,13 @@ PhaseStatus Compiler::placeLoopAlignInstructions()
weight_t minBlockSoFar = BB_MAX_WEIGHT;
BasicBlock* bbHavingAlign = nullptr;
BasicBlock::loopNumber currentAlignedLoopNum = BasicBlock::NOT_IN_LOOP;
bool visitedLoopNum[BasicBlock::MAX_LOOP_NUM];
memset(visitedLoopNum, false, sizeof(visitedLoopNum));

#ifdef DEBUG
unsigned visitedBlockForLoopNum[BasicBlock::MAX_LOOP_NUM];
memset(visitedBlockForLoopNum, 0, sizeof(visitedBlockForLoopNum));
#endif

if ((fgFirstBB != nullptr) && fgFirstBB->isLoopAlign())
{
Expand All @@ -5304,7 +5311,7 @@ PhaseStatus Compiler::placeLoopAlignInstructions()
}
}

// If there is a unconditional jump (which is not part of callf/always pair)
// If there is an unconditional jump (which is not part of callf/always pair)
if (opts.compJitHideAlignBehindJmp && (block->bbJumpKind == BBJ_ALWAYS) && !block->isBBCallAlwaysPairTail())
{
// Track the lower weight blocks
Expand Down Expand Up @@ -5358,12 +5365,19 @@ PhaseStatus Compiler::placeLoopAlignInstructions()
madeChanges = true;
unmarkedLoopAlign = true;
}
else if ((block->bbNatLoopNum != BasicBlock::NOT_IN_LOOP) && (block->bbNatLoopNum == loopTop->bbNatLoopNum))
else if ((loopTop->bbNatLoopNum != BasicBlock::NOT_IN_LOOP) && visitedLoopNum[loopTop->bbNatLoopNum])
{
#ifdef DEBUG
char buffer[100];
sprintf_s(buffer, 100, "loop block " FMT_BB " appears before top of loop",
visitedBlockForLoopNum[loopTop->bbNatLoopNum]);
#endif

// In some odd cases we may see blocks within the loop before we see the
// top block of the loop. Just bail on aligning such loops.
//
loopTop->unmarkLoopAlign(this DEBUG_ARG("loop block appears before top of loop"));

loopTop->unmarkLoopAlign(this DEBUG_ARG(buffer));
madeChanges = true;
unmarkedLoopAlign = true;
}
Expand Down Expand Up @@ -5398,6 +5412,20 @@ PhaseStatus Compiler::placeLoopAlignInstructions()
break;
}
}

if (block->bbNatLoopNum != BasicBlock::NOT_IN_LOOP)
{
#ifdef DEBUG
if (!visitedLoopNum[block->bbNatLoopNum])
{
// Record the first block for which bbNatLoopNum was seen for
// debugging purpose.
visitedBlockForLoopNum[block->bbNatLoopNum] = block->bbNum;
}
#endif
// If this block is part of loop, mark the loopNum as visited.
visitedLoopNum[block->bbNatLoopNum] = true;
}
}

assert(loopsToProcess == 0);
Expand Down