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Don't emit CFI instructions at the end of a function

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When functions are terminated by unreachable instructions, the last
instruction might trigger a CFI instruction to be generated. However,
emitting it would be be illegal since the function (and thus the FDE
the CFI is in) has already ended with the previous instruction.

Darwin's dwarfdump --verify --eh-frame complains about this and the
specification supports this.
Relevant bits from the DWARF 5 standard (6.4 Call Frame Information):

"[The] address_range [field in an FDE]: The number of bytes of
 program instructions described by this entry."

"Row creation instructions: [...]
 The new location value is always greater than the current one."
The first quotation implies that a CFI cannot describe a target
address outside of the enclosing FDE's range.

rdar://problem/26244988

Differential Revision: https://reviews.llvm.org/D32246

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@301219 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Adrian Prantl 2017-04-24 18:45:59 +00:00
parent 6f76a43cea
commit 83092adef9
5 changed files with 24 additions and 21 deletions
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10
lib/CodeGen/AsmPrinter/AsmPrinter.cpp
View File

@ -938,6 +938,16 @@ void AsmPrinter::emitCFIInstruction(const MachineInstr &MI) {
if (needsCFIMoves() == CFI_M_None)
return;
// If there is no "real" instruction following this CFI instruction, skip
// emitting it; it would be beyond the end of the function's FDE range.
auto *MBB = MI.getParent();
auto I = std::next(MI.getIterator());
while (I != MBB->end() && I->isTransient())
++I;
if (I == MBB->instr_end() &&
MBB->getReverseIterator() == MBB->getParent()->rbegin())
return;
const std::vector<MCCFIInstruction> &Instrs = MF->getFrameInstructions();
unsigned CFIIndex = MI.getOperand(0).getCFIIndex();
const MCCFIInstruction &CFI = Instrs[CFIIndex];

6
test/CodeGen/PowerPC/empty-functions.ll
View File

@ -24,9 +24,7 @@ entry:
; LINUX-NO-FP-NEXT: .size func, .L[[END]]-.L[[BEGIN]]
; LINUX-NO-FP-NEXT: .cfi_endproc
; A cfi directive can point to the end of a function. It (and in fact the
; entire body) could be optimized out because of the unreachable, but we
; don't do it right now.
; A cfi directive cannot point to the end of a function.
; LINUX-FP: func:
; LINUX-FP-NEXT: {{^}}.L[[BEGIN:.*]]:{{$}}
; LINUX-FP-NEXT: .cfi_startproc
@ -38,8 +36,6 @@ entry:
; LINUX-FP-NEXT: {{^}}.L{{.*}}:{{$}}
; LINUX-FP-NEXT: .cfi_offset r31, -4
; LINUX-FP-NEXT: mr 31, 1
; LINUX-FP-NEXT:{{^}}.L{{.*}}:{{$}}
; LINUX-FP-NEXT: .cfi_def_cfa_register r31
; LINUX-FP-NEXT: {{^}}.L[[END:.*]]:{{$}}
; LINUX-FP-NEXT: .size func, .L[[END]]-.L[[BEGIN]]
; LINUX-FP-NEXT: .cfi_endproc

10
test/CodeGen/SPARC/empty-functions.ll
View File

@ -14,19 +14,11 @@ entry:
; LINUX-NO-FP-NEXT: .size func, .L{{.*}}-func
; LINUX-NO-FP-NEXT: .cfi_endproc
; A cfi directive can point to the end of a function. It (and in fact the
; entire body) could be optimized out because of the unreachable, but we
; don't do it right now.
; A cfi directive cannot point to the end of a function.
; LINUX-FP: func:
; LINUX-FP-NEXT: .cfi_startproc
; LINUX-FP-NEXT: {{^}}!
; LINUX-FP-NEXT: save %sp, -96, %sp
; LINUX-FP-NEXT: {{^}}.L{{.*}}:{{$}}
; LINUX-FP-NEXT: .cfi_def_cfa_register %fp
; LINUX-FP-NEXT: {{^}}.L{{.*}}:{{$}}
; LINUX-FP-NEXT: .cfi_window_save
; LINUX-FP-NEXT: {{^}}.L{{.*}}:{{$}}
; LINUX-FP-NEXT: .cfi_register 15, 31
; LINUX-FP-NEXT: {{^}}.L{{.*}}:{{$}}
; LINUX-FP-NEXT: .size func, .Lfunc_end0-func
; LINUX-FP-NEXT: .cfi_endproc

11
test/CodeGen/X86/eh-frame-unreachable.ll Normal file
View File

@ -0,0 +1,11 @@
; RUN: llc < %s -mtriple=x86_64-apple-darwin | FileCheck %s
; Test that we don't emit a row that extends beyond the FDE's range_size.
;
; CHECK: movq %rsp, %rbp
; CHECK-NEXT: .cfi_endproc
; CHECK-NOT: .cfi
define void @f() #0 {
unreachable
}
attributes #0 = { "no-frame-pointer-elim"="true" }

8
test/CodeGen/X86/empty-functions.ll
View File

@ -23,8 +23,6 @@ entry:
; CHECK-FP-NEXT: :
; CHECK-FP-NEXT: .cfi_offset %rbp, -16
; CHECK-FP-NEXT: movq %rsp, %rbp
; CHECK-FP-NEXT: :
; CHECK-FP-NEXT: .cfi_def_cfa_register %rbp
; CHECK-FP-NEXT: .cfi_endproc
; An empty function is perfectly fine on ELF.
@ -35,9 +33,7 @@ entry:
; LINUX-NO-FP-NEXT: .size func, .L{{.*}}-func
; LINUX-NO-FP-NEXT: .cfi_endproc
; A cfi directive can point to the end of a function. It (and in fact the
; entire body) could be optimized out because of the unreachable, but we
; don't do it right now.
; A cfi directive cannot point to the end of a function.
; LINUX-FP: func:
; LINUX-FP-NEXT: .cfi_startproc
; LINUX-FP-NEXT: {{^}}#
@ -48,7 +44,5 @@ entry:
; LINUX-FP-NEXT: .cfi_offset %rbp, -16
; LINUX-FP-NEXT: movq %rsp, %rbp
; LINUX-FP-NEXT:{{^}}.L{{.*}}:{{$}}
; LINUX-FP-NEXT: .cfi_def_cfa_register %rbp
; LINUX-FP-NEXT:{{^}}.L{{.*}}:{{$}}
; LINUX-FP-NEXT: .size func, .Lfunc_end0-func
; LINUX-FP-NEXT: .cfi_endproc