On 6 October 2016 at 15:50, David Blaikie <dblai...@gmail.com> wrote:
> > > On Thu, Oct 6, 2016 at 6:16 AM Alex Lorenz <arpha...@gmail.com> wrote: > >> arphaman created this revision. >> arphaman added reviewers: dblaikie, krememek. >> arphaman added a subscriber: cfe-commits. >> arphaman set the repository for this revision to rL LLVM. >> >> This patch fixes the issue of clang emitting an unreachable warning when >> it encounters unreachable `__builtin_unreachable()` statements. It detects >> references to `__builtin_unreachable` and doesn't emit an unreachable >> warning for them. >> >> >> Repository: >> rL LLVM >> >> https://reviews.llvm.org/D25321 >> >> Files: >> lib/Analysis/ReachableCode.cpp >> test/Sema/warn-unreachable.c >> >> >> Index: test/Sema/warn-unreachable.c >> =================================================================== >> --- test/Sema/warn-unreachable.c >> +++ test/Sema/warn-unreachable.c >> @@ -396,3 +396,40 @@ >> else >> calledFun(); >> } >> + >> +int pr13910_foo(int x) { >> + if (x == 1) >> + return 0; >> + else >> + return x; >> + __builtin_unreachable(); // expected no warning >> +} >> + >> +int pr13910_bar(int x) { >> + switch (x) { >> + default: >> + return x + 1; >> + } >> + pr13910_foo(x); // expected-warning {{code will never be executed}} >> +} >> + >> +int pr13910_bar2(int x) { >> + if (x == 1) >> + return 0; >> + else >> + return x; >> + pr13910_foo(x); // expected-warning {{code will never be >> executed}} >> + __builtin_unreachable(); // expected no warning >> + pr13910_foo(x); // expected-warning {{code will never be >> executed}} >> > > Seems strange to have two warnings here ^ is that a separate bug? > It seems that it might be, yeah. For example, clang emits two unreachable warnings for the two `foo` calls in this code: int foo() { return 0; } int bar(int x) { if (x == 0) return x + 1; else return x; foo(); return 0; foo(); } But just one when the `return 0` that's between the two `foo` calls is removed. It doesn't seem like there's a PR for this issue, I'll file one later on today. > > >> +} >> + >> +void pr13910_noreturn() { >> + raze(); >> + __builtin_unreachable(); // expected no warning >> +} >> + >> +void pr13910_assert() { >> + myassert(0 && "unreachable"); >> + return; >> + __builtin_unreachable(); // expected no warning >> +} >> Index: lib/Analysis/ReachableCode.cpp >> =================================================================== >> --- lib/Analysis/ReachableCode.cpp >> +++ lib/Analysis/ReachableCode.cpp >> @@ -58,6 +58,15 @@ >> return false; >> } >> >> +static bool isBuiltinUnreachable(const CFGBlock *B, const Stmt *S) { >> + if (const DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(S)) { >> + const FunctionDecl *FDecl = dyn_cast<FunctionDecl>(DRE->getDecl()); >> + return FDecl && FDecl->getIdentifier() && >> + FDecl->getBuiltinID() == Builtin::BI__builtin_unreachable; >> + } >> + return false; >> +} >> + >> static bool isDeadReturn(const CFGBlock *B, const Stmt *S) { >> // Look to see if the current control flow ends with a 'return', and >> see if >> // 'S' is a substatement. The 'return' may not be the last element in >> the >> @@ -574,8 +583,7 @@ >> >> if (isa<BreakStmt>(S)) { >> UK = reachable_code::UK_Break; >> - } >> - else if (isTrivialDoWhile(B, S)) { >> + } else if (isTrivialDoWhile(B, S) || isBuiltinUnreachable(B, S)) { >> return; >> } >> else if (isDeadReturn(B, S)) { >> >> >>
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