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[SimplifyCFG] Do not blindly remove unreachable blocks 

DeleteDeadBlock was called indiscriminately, leading to cleanuprets with
undef cleanuppad references.

Instead, try to drain the BB of most of it's instructions if it is
unreachable.  We can then remove the BB if it solely consists of a
terminator (and maybe some phis).

llvm-svn: 261731
This commit is contained in:
David Majnemer 2016-02-24 10:02:16 +00:00
parent e2ad73759d
commit ec72e37220
2 changed files with 51 additions and 3 deletions
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8
llvm/lib/Transforms/Utils/SimplifyCFG.cpp
View File

@ -5278,10 +5278,18 @@ bool SimplifyCFGOpt::run(BasicBlock *BB) {
if ((pred_empty(BB) &&
BB != &BB->getParent()->getEntryBlock()) ||
BB->getSinglePredecessor() == BB) {
// Get the block mostly empty.
Changed |= removeAllNonTerminatorAndEHPadInstructions(BB) > 0;
// Now, verify that we succeeded getting the block empty.
// This will not be the case if this unreachable BB creates a token which is
// consumed by other unreachable blocks.
Instruction *FirstNonPHI = BB->getFirstNonPHI();
if (isa<TerminatorInst>(FirstNonPHI) && FirstNonPHI->use_empty()) {
DEBUG(dbgs() << "Removing BB: \n" << *BB);
DeleteDeadBlock(BB);
return true;
}
}
// Check to see if we can constant propagate this terminator instruction
// away...

40
llvm/test/Transforms/SimplifyCFG/unreachable-cleanuppad.ll Normal file
View File

@ -0,0 +1,40 @@
; RUN: opt -simplifycfg -S < %s | FileCheck %s
target datalayout = "e-m:x-p:32:32-i64:64-f80:32-n8:16:32-a:0:32-S32"
target triple = "i686-pc-win32"
declare i32 @__CxxFrameHandler3(...)
declare void @fn_2()
define void @fn_1(i1 %B) personality i32 (...)* @__CxxFrameHandler3 {
entry:
br i1 %B, label %__Ea.exit, label %lor.lhs.false.i.i
lor.lhs.false.i.i:
br i1 %B, label %if.end.i.i, label %__Ea.exit
if.end.i.i:
invoke void @fn_2()
to label %__Ea.exit unwind label %ehcleanup.i
ehcleanup.i:
%t4 = cleanuppad within none []
br label %arraydestroy.body.i
arraydestroy.body.i:
%gep = getelementptr i8, i8* null, i32 -1
br label %dtor.exit.i
dtor.exit.i:
br i1 %B, label %arraydestroy.done3.i, label %arraydestroy.body.i
arraydestroy.done3.i:
cleanupret from %t4 unwind to caller
__Ea.exit:
ret void
}
; CHECK-LABEL: define void @fn_1(
; CHECK-NEXT: entry:
; CHECK-NEXT: ret void