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Update PHI node example in README to use more idiomatic structure #88

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Merged
merged 2 commits into from
May 6, 2017
Merged

Update PHI node example in README to use more idiomatic structure #88

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b5d1f83
Update PHI node example to use proper semantics
Jumhyn May 5, 2017
4721e72
In PHI node example, store to local then return
Jumhyn May 6, 2017
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14 changes: 7 additions & 7 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -103,7 +103,7 @@ let function = builder.addFunction(
let entryBB = function.appendBasicBlock(named: "entry")
builder.positionAtEnd(of: entryBB)

// allocate space for a local value
// allocate space for a local value
let local = builder.buildAlloca(type: FloatType.double, name: "local")

// Compare to the condition
Expand All @@ -120,15 +120,13 @@ builder.buildCondBr(condition: test, then: thenBB, else: elseBB)
builder.positionAtEnd(of: thenBB)
// local = 1/89, the fibonacci series (sort of)
let thenVal = FloatType.double.constant(1/89)
builder.buildStore(thenVal, to: local)
// Branch to the merge block
builder.buildBr(mergeBB)

// MARK: Else Block
builder.positionAtEnd(of: elseBB)
// local = 1/109, the fibonacci series (sort of) backwards
let elseVal = FloatType.double.constant(1/109)
builder.buildStore(elseVal, to: local)
// Branch to the merge block
builder.buildBr(mergeBB)

Expand All @@ -139,7 +137,9 @@ phi.addIncoming([
(thenVal, thenBB),
(elseVal, elseBB),
])
builder.buildRet(phi)
builder.buildStore(phi, to: local)
let ret = builder.buildLoad(local, name: "ret")
builder.buildRet(ret)
```

This program generates the following IR:
Expand All @@ -152,16 +152,16 @@ entry:
br i1 %1, label %then, label %else

then: ; preds = %entry
store double 0x3F8702E05C0B8170, double* %local
br label %merge

else: ; preds = %entry
store double 0x3F82C9FB4D812CA0, double* %local
br label %merge

merge: ; preds = %else, %then
%phi_example = phi double [ 0x3F8702E05C0B8170, %then ], [ 0x3F82C9FB4D812CA0, %else ]
ret double %phi_example
store double %phi_example, double* %local
%ret = load double, double* %local
ret double %ret
}
```

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