3d08ade7bd
This patch is part of a set of patches that add an `-fextend-lifetimes` flag to clang, which extends the lifetimes of local variables and parameters for improved debuggability. In addition to that flag, the patch series adds a pragma to selectively disable `-fextend-lifetimes`, and an `-fextend-this-ptr` flag which functions as `-fextend-lifetimes` for this pointers only. All changes and tests in these patches were written by Wolfgang Pieb (@wolfy1961), while Stephen Tozer (@SLTozer) has handled review and merging. The extend lifetimes flag is intended to eventually be set on by `-Og`, as discussed in the RFC here: https://discourse.llvm.org/t/rfc-redefine-og-o1-and-add-a-new-level-of-og/72850 This patch implements a new intrinsic instruction in LLVM, `llvm.fake.use` in IR and `FAKE_USE` in MIR, that takes a single operand and has no effect other than "using" its operand, to ensure that its operand remains live until after the fake use. This patch does not emit fake uses anywhere; the next patch in this sequence causes them to be emitted from the clang frontend, such that for each variable (or this) a fake.use operand is inserted at the end of that variable's scope, using that variable's value. This patch covers everything post-frontend, which is largely just the basic plumbing for a new intrinsic/instruction, along with a few steps to preserve the fake uses through optimizations (such as moving them ahead of a tail call or translating them through SROA). Co-authored-by: Stephen Tozer <stephen.tozer@sony.com>
22 lines
584 B
LLVM
22 lines
584 B
LLVM
; RUN: opt -S -passes=sroa %s | FileCheck %s
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;
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;; Check that we do not assert and that we retain the fake_use instruction that
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;; uses the address of bar.
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;
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; CHECK: define{{.*}}foo
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; CHECK: call{{.*llvm\.fake\.use.*}}(ptr %bar.addr)
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define void @_Z3fooPi(ptr %bar) {
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entry:
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%bar.addr = alloca ptr, align 8
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%baz = alloca ptr, align 8
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store ptr %bar, ptr %bar.addr, align 8
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store ptr %bar.addr, ptr %baz, align 8
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%0 = load ptr, ptr %bar.addr, align 8
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%1 = load ptr, ptr %baz, align 8
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call void (...) @llvm.fake.use(ptr %1)
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ret void
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}
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declare void @llvm.fake.use(...)
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