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From C11 and C++11 onwards, a forward-progress requirement has been introduced for both languages. In the case of C, loops with non-constant conditionals that do not have any observable side-effects (as defined by 6.8.5p6) can be assumed by the implementation to terminate, and in the case of C++, this assumption extends to all functions. The clang frontend will emit the `mustprogress` function attribute for C++ functions (D86233, D85393, D86841) and emit the loop metadata `llvm.loop.mustprogress` for every loop in C11 or later that has a non-constant conditional. This patch modifies LoopDeletion so that only loops with the `llvm.loop.mustprogress` metadata or loops contained in functions that are required to make progress (`mustprogress` or `willreturn`) are checked for observable side-effects. If these loops do not have an observable side-effect, then we delete them. Loops without observable side-effects that do not satisfy the above conditions will not be deleted. Reviewed By: jdoerfert Differential Revision: https://reviews.llvm.org/D86844
21 lines
518 B
LLVM
21 lines
518 B
LLVM
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --function-signature --check-attributes
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; RUN: opt < %s -loop-deletion -S | FileCheck %s
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define void @f() #0 {
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; CHECK: Function Attrs: mustprogress
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; CHECK-LABEL: define {{[^@]+}}@f
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; CHECK-SAME: () [[ATTR0:#.*]] {
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; CHECK-NEXT: unreachable
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;
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br label %1
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%.01 = phi i32 [ 1, %0 ], [ %3, %2 ]
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%.0 = phi i32 [ 1, %0 ], [ %3, %2 ]
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br label %2
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%3 = add nsw i32 %.01, %.0
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br label %1
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}
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attributes #0 = { mustprogress }
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