Now that #149310 has restricted lifetime intrinsics to only work on
allocas, we can also drop the explicit size argument. Instead, the size
is implied by the alloca.
This removes the ability to only mark a prefix of an alloca alive/dead.
We never used that capability, so we should remove the need to handle
that possibility everywhere (though many key places, including stack
coloring, did not actually respect this).
Currently if an OpenMP program uses `linear` clause, and is compiled with
optimization, `llvm.lifetime.end` for variables listed in `linear` clause are
emitted too early such that there could still be uses after that. Let's take the
following code as example:
```
// loop.c
int j;
int *u;
void loop(int n) {
int i;
for (i = 0; i < n; ++i) {
++j;
u = &j;
}
}
```
We compile using the command:
```
clang -cc1 -fopenmp-simd -O3 -x c -triple x86_64-apple-darwin10 -emit-llvm loop.c -o loop.ll
```
The following IR (simplified) will be generated:
```
@j = local_unnamed_addr global i32 0, align 4
@u = local_unnamed_addr global ptr null, align 8
define void @loop(i32 noundef %n) local_unnamed_addr {
entry:
%j = alloca i32, align 4
%cmp = icmp sgt i32 %n, 0
br i1 %cmp, label %simd.if.then, label %simd.if.end
simd.if.then: ; preds = %entry
call void @llvm.lifetime.start.p0(i64 4, ptr nonnull %j)
store ptr %j, ptr @u, align 8
call void @llvm.lifetime.end.p0(i64 4, ptr nonnull %j)
%0 = load i32, ptr %j, align 4
store i32 %0, ptr @j, align 4
br label %simd.if.end
simd.if.end: ; preds = %simd.if.then, %entry
ret void
}
```
The most important part is:
```
call void @llvm.lifetime.end.p0(i64 4, ptr nonnull %j)
%0 = load i32, ptr %j, align 4
store i32 %0, ptr @j, align 4
```
`%j` is still loaded after `@llvm.lifetime.end.p0(i64 4, ptr nonnull %j)`. This
could cause the backend incorrectly optimizes the code and further generates
incorrect code. The root cause is, when we emit a construct that could have
`linear` clause, it usually has the following pattern:
```
EmitOMPLinearClauseInit(S)
{
OMPPrivateScope LoopScope(*this);
...
EmitOMPLinearClause(S, LoopScope);
...
(void)LoopScope.Privatize();
...
}
EmitOMPLinearClauseFinal(S, [](CodeGenFunction &) { return nullptr; });
```
Variables that need to be privatized are added into `LoopScope`, which also
serves as a RAII object. When `LoopScope` is destructed and if optimization is
enabled, a `@llvm.lifetime.end` is also emitted for each privatized variable.
However, the writing back to original variables in `linear` clause happens after
the scope in `EmitOMPLinearClauseFinal`, causing the issue we see above.
A quick "fix" seems to be, moving `EmitOMPLinearClauseFinal` inside the scope.
However, it doesn't work. That's because the local variable map has been updated
by `LoopScope` such that a variable declaration is mapped to the privatized
variable, instead of the actual one. In that way, the following code will be
generated:
```
%0 = load i32, ptr %j, align 4
store i32 %0, ptr %j, align 4
call void @llvm.lifetime.end.p0(i64 4, ptr nonnull %j)
```
Well, now the life time is correct, but apparently the writing back is broken.
In this patch, a new function `OMPPrivateScope::restoreMap` is added and called
before calling `EmitOMPLinearClauseFinal`. This can make sure that
`EmitOMPLinearClauseFinal` can find the orignal varaibls to write back.
Fixes#56913.
Reviewed By: ABataev
Differential Revision: https://reviews.llvm.org/D131272
