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compiler: make composite map hashes order dependent

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Use the same multiply-and-XOR combination as the runtime interface hash for generated struct and array key hashes. This avoids systematic collisions when components are permuted.
This commit is contained in:
Jake Bailey
2026-08-31 08:31:52 -07:00
committed by Ron Evans
parent 7d4b42db83
commit 2761414777
2 changed files with 19 additions and 14 deletions
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compiler/map.go
+5 -3
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@@ -417,6 +417,7 @@ func (b *builder) generateKeyHash(keyType types.Type, llvmKeyType llvm.Type, key
return b.createRuntimeCall("hashmapInterfacePtrHash", []llvm.Value{keyPtr, size, seed}, "hash")
case *types.Struct:
hash := llvm.ConstInt(b.ctx.Int32Type(), 0, false)
multiplier := llvm.ConstInt(b.ctx.Int32Type(), 31, false)
zero := llvm.ConstInt(b.ctx.Int32Type(), 0, false)
for i := 0; i < keyType.NumFields(); i++ {
if keyType.Field(i).Name() == "_" {
@@ -430,7 +431,7 @@ func (b *builder) generateKeyHash(keyType types.Type, llvmKeyType llvm.Type, key
idx := llvm.ConstInt(b.ctx.Int32Type(), uint64(i), false)
fieldPtr := b.CreateInBoundsGEP(llvmKeyType, keyPtr, []llvm.Value{zero, idx}, "")
fieldHash := b.generateKeyHash(fieldType, llvmFieldType, fieldPtr, seed)
hash = b.CreateXor(hash, fieldHash, "")
hash = b.CreateXor(b.CreateMul(hash, multiplier, ""), fieldHash, "")
}
return hash
case *types.Array:
@@ -445,6 +446,7 @@ func (b *builder) generateKeyHash(keyType types.Type, llvmKeyType llvm.Type, key
if arrayLen == 0 {
return llvm.ConstInt(b.ctx.Int32Type(), 0, false)
}
multiplier := llvm.ConstInt(b.ctx.Int32Type(), 31, false)
if arrayLen <= hashArrayUnrollLimit {
hash := llvm.ConstInt(b.ctx.Int32Type(), 0, false)
zero := llvm.ConstInt(b.ctx.Int32Type(), 0, false)
@@ -452,7 +454,7 @@ func (b *builder) generateKeyHash(keyType types.Type, llvmKeyType llvm.Type, key
idx := llvm.ConstInt(b.uintptrType, uint64(i), false)
elemPtr := b.CreateInBoundsGEP(llvmKeyType, keyPtr, []llvm.Value{zero, idx}, "")
elemHash := b.generateKeyHash(elemType, llvmElemType, elemPtr, seed)
hash = b.CreateXor(hash, elemHash, "")
hash = b.CreateXor(b.CreateMul(hash, multiplier, ""), elemHash, "")
}
return hash
}
@@ -471,7 +473,7 @@ func (b *builder) generateKeyHash(keyType types.Type, llvmKeyType llvm.Type, key
elemPtr := b.CreateInBoundsGEP(llvmKeyType, keyPtr, []llvm.Value{zero, phiI}, "")
elemHash := b.generateKeyHash(elemType, llvmElemType, elemPtr, seed)
newHash := b.CreateXor(phiHash, elemHash, "")
newHash := b.CreateXor(b.CreateMul(phiHash, multiplier, ""), elemHash, "")
nextI := b.CreateAdd(phiI, llvm.ConstInt(b.uintptrType, 1, false), "")
cond := b.CreateICmp(llvm.IntULT, nextI, llvm.ConstInt(b.uintptrType, uint64(arrayLen), false), "")
b.CreateCondBr(cond, loopBody, loopDone)