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[PruneEH] A naked, noinline function can return via InlineAsm

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The PruneEH pass tries to annotate functions as 'noreturn' if it doesn't
see a ReturnInst.  However, a naked function containing inline assembly
can contain control flow leaving the function.

This fixes PR23971.

llvm-svn: 240876
This commit is contained in:
David Majnemer 2015-06-27 07:52:53 +00:00
parent 5cd04c2d39
commit bce3d2c083
2 changed files with 59 additions and 25 deletions
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63
lib/Transforms/IPO/PruneEH.cpp
View File

@ -25,6 +25,7 @@
#include "llvm/IR/CFG.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/InlineAsm.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/LLVMContext.h"
@ -97,42 +98,54 @@ bool PruneEH::runOnSCC(CallGraphSCC &SCC) {
} else {
bool CheckUnwind = !SCCMightUnwind && !F->doesNotThrow();
bool CheckReturn = !SCCMightReturn && !F->doesNotReturn();
// Determine if we should scan for InlineAsm in a naked function as it
// is the only way to return without a ReturnInst. Only do this for
// no-inline functions as functions which may be inlined cannot
// meaningfully return via assembly.
bool CheckReturnViaAsm = CheckReturn &&
F->hasFnAttribute(Attribute::Naked) &&
F->hasFnAttribute(Attribute::NoInline);
if (!CheckUnwind && !CheckReturn)
continue;
// Check to see if this function performs an unwind or calls an
// unwinding function.
for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) {
if (CheckUnwind && isa<ResumeInst>(BB->getTerminator())) {
// Uses unwind / resume!
for (const BasicBlock &BB : *F) {
const TerminatorInst *TI = BB.getTerminator();
if (CheckUnwind && TI->mayThrow()) {
SCCMightUnwind = true;
} else if (CheckReturn && isa<ReturnInst>(BB->getTerminator())) {
} else if (CheckReturn && isa<ReturnInst>(TI)) {
SCCMightReturn = true;
}
// Invoke instructions don't allow unwinding to continue, so we are
// only interested in call instructions.
if (CheckUnwind && !SCCMightUnwind)
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
if (CallInst *CI = dyn_cast<CallInst>(I)) {
if (CI->doesNotThrow()) {
// This call cannot throw.
} else if (Function *Callee = CI->getCalledFunction()) {
for (const Instruction &I : BB) {
if ((!CheckUnwind || SCCMightUnwind) &&
(!CheckReturnViaAsm || SCCMightReturn))
break;
// Check to see if this function performs an unwind or calls an
// unwinding function.
if (CheckUnwind && !SCCMightUnwind && I.mayThrow()) {
bool InstMightUnwind = true;
if (const auto *CI = dyn_cast<CallInst>(&I)) {
if (Function *Callee = CI->getCalledFunction()) {
CallGraphNode *CalleeNode = CG[Callee];
// If the callee is outside our current SCC then we may
// throw because it might.
if (!SCCNodes.count(CalleeNode)) {
SCCMightUnwind = true;
break;
}
} else {
// Indirect call, it might throw.
SCCMightUnwind = true;
break;
// If the callee is outside our current SCC then we may throw
// because it might. If it is inside, do nothing.
if (SCCNodes.count(CalleeNode) > 0)
InstMightUnwind = false;
}
}
if (SCCMightUnwind && SCCMightReturn) break;
SCCMightUnwind |= InstMightUnwind;
}
if (CheckReturnViaAsm && !SCCMightReturn)
if (auto ICS = ImmutableCallSite(&I))
if (const auto *IA = dyn_cast<InlineAsm>(ICS.getCalledValue()))
if (IA->hasSideEffects())
SCCMightReturn = true;
}
if (SCCMightUnwind && SCCMightReturn)
break;
}
}
}

21
test/Transforms/PruneEH/pr23971.ll Normal file
View File

@ -0,0 +1,21 @@
; RUN: opt -S -prune-eh < %s | FileCheck %s
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
define void @f() #0 {
entry:
call void asm sideeffect "ret\0A\09", "~{dirflag},~{fpsr},~{flags}"()
unreachable
}
define i32 @g() {
entry:
call void @f()
ret i32 42
}
; CHECK-LABEL: define i32 @g()
; CHECK: ret i32 42
attributes #0 = { naked noinline }