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Consider this function:

Browse Source 
void foo() { __builtin_unreachable(); }

It will output the following on Darwin X86:

_func1:
Leh_func_begin0:
        pushq %rbp
Ltmp0:
        movq %rsp, %rbp
Ltmp1:
Leh_func_end0:

This prolog adds a new Call Frame Information (CFI) row to the FDE with an
address that is not within the address range of the code it describes -- part is
equal to the end of the function -- and therefore results in an invalid EH
frame. If we emit a nop in this situation, then the CFI row is now within the
address range.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@108568 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Bill Wendling 2010-07-16 22:51:10 +00:00
parent 78e6e00922
commit dc86704114
5 changed files with 39 additions and 18 deletions
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14
lib/CodeGen/AsmPrinter/AsmPrinter.cpp
View File

@ -599,12 +599,15 @@ void AsmPrinter::EmitFunctionBody() {
// Print out code for the function.
bool HasAnyRealCode = false;
const MachineInstr *LastMI = 0;
for (MachineFunction::const_iterator I = MF->begin(), E = MF->end();
I != E; ++I) {
// Print a label for the basic block.
EmitBasicBlockStart(I);
for (MachineBasicBlock::const_iterator II = I->begin(), IE = I->end();
II != IE; ++II) {
LastMI = II;
// Print the assembly for the instruction.
if (!II->isLabel() && !II->isImplicitDef() && !II->isKill() &&
!II->isDebugValue()) {
@ -652,11 +655,18 @@ void AsmPrinter::EmitFunctionBody() {
}
}
}
// If the last instruction was a prolog label, then we have a situation where
// we emitted a prolog but no function body. This results in the ending prolog
// label equaling the end of function label and an invalid "row" in the
// FDE. We need to emit a noop in this situation so that the FDE's rows are
// valid.
bool RequiresNoop = LastMI && LastMI->getOpcode()==TargetOpcode::PROLOG_LABEL;
// If the function is empty and the object file uses .subsections_via_symbols,
// then we need to emit *something* to the function body to prevent the
// labels from collapsing together. Just emit a noop.
if (MAI->hasSubsectionsViaSymbols() && !HasAnyRealCode) {
if ((MAI->hasSubsectionsViaSymbols() && !HasAnyRealCode) || RequiresNoop) {
MCInst Noop;
TM.getInstrInfo()->getNoopForMachoTarget(Noop);
if (Noop.getOpcode()) {

8
test/CodeGen/PowerPC/2008-01-25-EmptyFunction.ll
View File

@ -1,8 +0,0 @@
; RUN: llc < %s -march=ppc32 | grep nop
target triple = "powerpc-apple-darwin8"
define void @bork() noreturn nounwind {
entry:
unreachable
}

12
test/CodeGen/PowerPC/empty-functions.ll Normal file
View File

@ -0,0 +1,12 @@
; RUN: llc < %s -mtriple=powerpc-apple-darwin | FileCheck -check-prefix=CHECK-NO-FP %s
; RUN: llc < %s -mtriple=powerpc-apple-darwin -disable-fp-elim | FileCheck -check-prefix=CHECK-FP %s
define void @func() {
entry:
unreachable
}
; CHECK-NO-FP: _func:
; CHECK-NO-FP: nop
; CHECK-FP: _func:
; CHECK-FP: nop

8
test/CodeGen/X86/2008-01-25-EmptyFunction.ll
View File

@ -1,8 +0,0 @@
; RUN: llc < %s -march=x86 | grep nop
target triple = "i686-apple-darwin8"
define void @bork() noreturn nounwind {
entry:
unreachable
}

15
test/CodeGen/X86/empty-functions.ll Normal file
View File

@ -0,0 +1,15 @@
; RUN: llc < %s -mtriple=x86_64-apple-darwin | FileCheck -check-prefix=CHECK-NO-FP %s
; RUN: llc < %s -mtriple=x86_64-apple-darwin -disable-fp-elim | FileCheck -check-prefix=CHECK-FP %s
define void @func() {
entry:
unreachable
}
; CHECK-NO-FP: _func:
; CHECK-NO-FP-NOT: movq %rsp, %rbp
; CHECK-NO-FP: nop
; CHECK-FP: _func:
; CHECK-FP: movq %rsp, %rbp
; CHECK-FP-NEXT: Ltmp1:
; CHECK-FP: nop