[SOL] Allow branch folding to run in SBF #154
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LucasSte
commented
Jun 16, 2025
| TBB = I->getOperand(0).getMBB(); | ||
| continue; | ||
| } | ||
| // If the block has no terminators, it just falls into the block after it. |
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This new implementation is from here:
| I->eraseFromParent(); | ||
| I = MBB.end(); | ||
| ++Count; | ||
| MachineBasicBlock::iterator I = MBB.getLastNonDebugInstr(); |
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This one is from here:
Lichtso
approved these changes
Jun 18, 2025
LucasSte
merged commit 1fa01f5
into
anza-xyz:solana-rustc/19.1-2024-12-03
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Problem
The SBF codegen has been generating awkward code for branches, particularly doing:
While it could be doing:
This happens because LLVM branch folding pass did not have enough information to simplify branches.
Solution
analyzeBranch,insertBranch,reverseBranchCondition,removeBranchandgetBranchDestBlockcorrectly. I copied some functions from the aarch64 target, with specific adaptations for the SBF target.getInstSizeInBytes, which LLVM uses in the branch relaxing pass.PS: I got mixed results, because branch folding runs multiple times in codegen. Now that LLVM has information about branches, programs changed completely. Branches are now different, some instructions are sunken, while others are hoisted. Register allocation also changed in some cases.