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SSA: Remove some shuffler logic #16600

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17 changes: 0 additions & 17 deletions libyul/backends/evm/ssa/StackShuffler.h
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Original file line number Diff line number Diff line change
Expand Up @@ -446,23 +446,6 @@ class StackShuffler
_stack.swap(offset);
return {ShuffleHelperResult::Status::StackModified};
}

// try swapping top with a tail slot that has what we need at top
for (StackOffset tailOffset: _state.stackTailRange())
if (
_stack.isValidSwapTarget(tailOffset) &&
_state.isArgsCompatible(tailOffset, stackTop) &&
(!_state.requiredInTail(_stack[tailOffset]) || _state.countInTail(_stack[tailOffset]) > 1) &&
// current top can safely go to tail (not needed in args, or we have excess)
(
!_state.requiredInArgs(_stack[stackTop]) ||
_state.countInArgs(_stack[stackTop]) > _state.targetArgsCount(_stack[stackTop])
)
)
{
_stack.swap(tailOffset);
return {ShuffleHelperResult::Status::StackModified};
}
}

// swap up any slot in args that is out of position and has a slot available in args that it can occupy
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8 changes: 4 additions & 4 deletions test/libsolidity/semanticTests/externalContracts/base64.sol
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Expand Up @@ -41,8 +41,8 @@ contract test {
// gas legacy code: 629800
// gas legacyOptimized: 87926
// gas legacyOptimized code: 429800
// gas ssaCFGOptimized: 79931
// gas ssaCFGOptimized code: 332600
// gas ssaCFGOptimized: 79867
// gas ssaCFGOptimized code: 331800
// encode_inline_asm(bytes): 0x20, 0 -> 0x20, 0
// encode_inline_asm(bytes): 0x20, 1, "f" -> 0x20, 4, "Zg=="
// encode_inline_asm(bytes): 0x20, 2, "fo" -> 0x20, 4, "Zm8="
Expand All @@ -61,9 +61,9 @@ contract test {
// gas irOptimized: 1406025
// gas legacy: 1554038
// gas legacyOptimized: 1132031
// gas ssaCFGOptimized: 1388025
// gas ssaCFGOptimized: 1386025
// encode_no_asm_large()
// gas irOptimized: 3512081
// gas legacy: 4600082
// gas legacyOptimized: 2813075
// gas ssaCFGOptimized: 3089081
// gas ssaCFGOptimized: 3078081
4 changes: 2 additions & 2 deletions test/libsolidity/semanticTests/externalContracts/deposit_contract.sol
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Expand Up @@ -185,8 +185,8 @@ contract DepositContract is IDepositContract, ERC165 {
// gas legacy code: 1438800
// gas legacyOptimized: 848699
// gas legacyOptimized code: 878200
// gas ssaCFGOptimized: 809663
// gas ssaCFGOptimized code: 570000
// gas ssaCFGOptimized: 809711
// gas ssaCFGOptimized code: 570600
Comment on lines -188 to +189
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@blishko blishko Apr 15, 2026

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This is a small regression, but it is the only one on external contracts.

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@clonker clonker Apr 16, 2026

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regression by 0.0059% for runtime and by 0.105% for deploy.. i think it's fine..

// supportsInterface(bytes4): 0x0 -> 0
// supportsInterface(bytes4): 0xffffffff00000000000000000000000000000000000000000000000000000000 -> false # defined to be false by ERC-165 #
// supportsInterface(bytes4): 0x01ffc9a700000000000000000000000000000000000000000000000000000000 -> true # ERC-165 id #
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4 changes: 2 additions & 2 deletions test/libsolidity/semanticTests/externalContracts/ramanujan_pi.sol
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Expand Up @@ -42,8 +42,8 @@ contract test {
// gas legacy code: 523600
// gas legacyOptimized: 82667
// gas legacyOptimized code: 369200
// gas ssaCFGOptimized: 77956
// gas ssaCFGOptimized code: 313400
// gas ssaCFGOptimized: 77788
// gas ssaCFGOptimized code: 311000
// prb_pi() -> 3141592656369545286
// gas irOptimized: 55036
// gas legacy: 100657
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4 changes: 2 additions & 2 deletions test/libsolidity/semanticTests/externalContracts/snark.sol
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Expand Up @@ -297,10 +297,10 @@ contract Test {
// gas irOptimized: 275229
// gas legacy: 293579
// gas legacyOptimized: 276313
// gas ssaCFGOptimized: 275795
// gas ssaCFGOptimized: 275787
// verifyTx() -> true
// ~ emit Verified(string): 0x20, 0x16, "Successfully verified."
// gas irOptimized: 818076
// gas legacy: 904397
// gas legacyOptimized: 816770
// gas ssaCFGOptimized: 820130
// gas ssaCFGOptimized: 820110
6 changes: 3 additions & 3 deletions test/libsolidity/semanticTests/externalContracts/strings.sol
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Expand Up @@ -58,8 +58,8 @@ contract test {
// gas legacy code: 932600
// gas legacyOptimized: 102639
// gas legacyOptimized code: 612400
// gas ssaCFGOptimized: 96160
// gas ssaCFGOptimized code: 532200
// gas ssaCFGOptimized: 95989
// gas ssaCFGOptimized code: 530000
// toSlice(string): 0x20, 11, "hello world" -> 11, 0xa0
// gas irOptimized: 22646
// gas legacy: 23168
Expand All @@ -80,4 +80,4 @@ contract test {
// gas irOptimized: 1976778
// gas legacy: 4234020
// gas legacyOptimized: 2318668
// gas ssaCFGOptimized: 1882355
// gas ssaCFGOptimized: 1841235
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@blishko blishko Apr 15, 2026

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This is actually a 2% improvement.

6 changes: 3 additions & 3 deletions test/libyul/ssa/stackLayoutGenerator/nested_for.yul
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Expand Up @@ -107,11 +107,11 @@
// Block0_3 [label="\
// IN: [phi0, phi3, JUNK]\l\
// \l\
// [JUNK, phi3, lit2, phi0]\l\
// [phi3, lit2, phi0]\l\
// add\l\
// [JUNK, phi3, v5]\l\
// [phi3, v5]\l\
// \l\
// OUT: [JUNK, phi3, v5]\l\
// OUT: [phi3, v5]\l\
// "];
// Block0_3 -> Block0_3Exit [arrowhead=none];
// Block0_3Exit [label="Jump" shape=oval];
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3 changes: 2 additions & 1 deletion test/libyul/ssa/stackShuffler/swap_junk_over_pop.stack
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Expand Up @@ -8,7 +8,8 @@ targetStackSize: 4
// (initial)| v0 | * v2
// PUSH lit2| v0 | * v2 lit2
// SWAP2| v0 | lit2 v2 *
// SWAP3| * | lit2 v2 v0
// POP| v0 | lit2 v2
// DUP3| v0 | lit2 v2 v0
Comment on lines -11 to +12
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@blishko blishko Apr 15, 2026

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This is a bit unfortunate, I would like to fix this somehow.

// +------- +---------------------
// (target)| {} | lit2 v2 v0
// Status: Admissible