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[Coroutines] Add missing llvm.dbg.declare's to cover for more allocas
Tracking local variables across suspend points is still somewhat incomplete. Consider this coroutine snippet: ``` resumable foo() { int x[10] = {}; int a = 3; co_await std::experimental::suspend_always(); a++; x[0] = 1; a += 2; x[1] = 2; a += 3; x[2] = 3; } ``` Can't manage to print `a` or `x` if they turn out to be allocas during CoroSplit (which happens if you build this code with `-O0` prior to this commit): ``` * thread #1, queue = 'com.apple.main-thread', stop reason = step over frame #0: 0x0000000100003729 main-noprint`foo() at main-noprint.cpp:43:5 40 co_await std::experimental::suspend_always(); 41 a++; 42 x[0] = 1; -> 43 a += 2; 44 x[1] = 2; 45 a += 3; 46 x[2] = 3; (lldb) p x error: <user expression 21>:1:1: use of undeclared identifier 'x' x ^ ``` The generated IR contains a `llvm.dbg.declare` for `x` in it's initialization basic block. After CoroSplit, the `llvm.dbg.declare` might not dominate all of `x` uses and we lose debugging quality. Add `llvm.dbg.value`s to all relevant basic blocks such that if later transformations break the dominance the reliable debug info is already in place. For instance, this BB: ``` await.ready: ... %arrayidx = getelementptr inbounds [10 x i32], [10 x i32]* %x.reload.addr, i64 0, i64 0, !dbg !760 ... %arrayidx19 = getelementptr inbounds [10 x i32], [10 x i32]* %x.reload.addr, i64 0, i64 1, !dbg !763 ... %arrayidx21 = getelementptr inbounds [10 x i32], [10 x i32]* %x.reload.addr, i64 0, i64 2, !dbg !766 ``` becomes: ``` await.ready: ... call void @llvm.dbg.value(metadata [10 x i32]* %x.reload.addr, metadata !751, metadata !DIExpression()), !dbg !753 ... %arrayidx = getelementptr inbounds [10 x i32], [10 x i32]* %x.reload.addr, i64 0, i64 0, !dbg !760 ... %arrayidx19 = getelementptr inbounds [10 x i32], [10 x i32]* %x.reload.addr, i64 0, i64 1, !dbg !763 ... %arrayidx21 = getelementptr inbounds [10 x i32], [10 x i32]* %x.reload.addr, i64 0, i64 2, !dbg !766 ``` Differential Revision: https://reviews.llvm.org/D90772
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