Don't use dropflag hints when the type is dropless #30851
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(rust_highfive has picked a reviewer for you, use r? to override) |
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r? @pnkfelix |
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Ironically this same bug was just pointed out to me at lunch today. (I didn't have time to investigate as i have hands full with regression fixes at moment but will review this ASAP) |
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@bors r+ |
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📌 Commit e3abc3c has been approved by |
Manishearth
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to Manishearth/rust
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Jan 14, 2016
… r=pnkfelix
Apparently we allocate and maintain non-working dropflag hints since June... In anticipation of a working implementation of on-stack drop flag hints, let's not spend even more time on types that don't even need to be dropped.
```rust
fn main() {
let (i,j,k,l) = (0,0,0,0);
}
```
used to translate to (unoptimized only, of course):
```llvm
define internal void @_ZN4main20ha8deb085c47920d8eaaE() unnamed_addr #0 {
entry-block:
%dropflag_hint_10 = alloca i8
%dropflag_hint_11 = alloca i8
%dropflag_hint_12 = alloca i8
%dropflag_hint_13 = alloca i8
%const = alloca { i32, i32, i32, i32 }
%i = alloca i32
%j = alloca i32
%k = alloca i32
%l = alloca i32
store i8 61, i8* %dropflag_hint_10
store i8 61, i8* %dropflag_hint_11
store i8 61, i8* %dropflag_hint_12
store i8 61, i8* %dropflag_hint_13
%0 = bitcast { i32, i32, i32, i32 }* %const to i8*
call void @llvm.memcpy.p0i8.p0i8.i64(i8* %0, i8* bitcast ({ i32, i32, i32, i32 }* @const2752 to i8*), i64 16, i32 4, i1 false)
%1 = getelementptr inbounds { i32, i32, i32, i32 }, { i32, i32, i32, i32 }* %const, i32 0, i32 0
%2 = load i32, i32* %1, align 4
store i32 %2, i32* %i, align 4
%3 = getelementptr inbounds { i32, i32, i32, i32 }, { i32, i32, i32, i32 }* %const, i32 0, i32 1
%4 = load i32, i32* %3, align 4
store i32 %4, i32* %j, align 4
%5 = getelementptr inbounds { i32, i32, i32, i32 }, { i32, i32, i32, i32 }* %const, i32 0, i32 2
%6 = load i32, i32* %5, align 4
store i32 %6, i32* %k, align 4
%7 = getelementptr inbounds { i32, i32, i32, i32 }, { i32, i32, i32, i32 }* %const, i32 0, i32 3
%8 = load i32, i32* %7, align 4
store i32 %8, i32* %l, align 4
ret void
}
```
Now it gives:
```llvm
define internal void @_ZN4main20ha8deb085c47920d8eaaE() unnamed_addr #0 {
entry-block:
%const = alloca { i32, i32, i32, i32 }
%i = alloca i32
%j = alloca i32
%k = alloca i32
%l = alloca i32
%0 = bitcast { i32, i32, i32, i32 }* %const to i8*
call void @llvm.memcpy.p0i8.p0i8.i64(i8* %0, i8* bitcast ({ i32, i32, i32, i32 }* @const2748 to i8*), i64 16, i32 4, i1 false)
%1 = getelementptr inbounds { i32, i32, i32, i32 }, { i32, i32, i32, i32 }* %const, i32 0, i32 0
%2 = load i32, i32* %1, align 4
store i32 %2, i32* %i, align 4
%3 = getelementptr inbounds { i32, i32, i32, i32 }, { i32, i32, i32, i32 }* %const, i32 0, i32 1
%4 = load i32, i32* %3, align 4
store i32 %4, i32* %j, align 4
%5 = getelementptr inbounds { i32, i32, i32, i32 }, { i32, i32, i32, i32 }* %const, i32 0, i32 2
%6 = load i32, i32* %5, align 4
store i32 %6, i32* %k, align 4
%7 = getelementptr inbounds { i32, i32, i32, i32 }, { i32, i32, i32, i32 }* %const, i32 0, i32 3
%8 = load i32, i32* %7, align 4
store i32 %8, i32* %l, align 4
ret void
}
```
Let's hope I didn't break anything!
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Apparently we allocate and maintain non-working dropflag hints since June... In anticipation of a working implementation of on-stack drop flag hints, let's not spend even more time on types that don't even need to be dropped.
used to translate to (unoptimized only, of course):
Now it gives:
Let's hope I didn't break anything!