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Make DeadArgumentElimination more conservative on variadic functions

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Variadic functions are particularly fragile in the face of ABI changes, so this
limits how much the pass changes them

llvm-svn: 183625
This commit is contained in:
Tim Northover 2013-06-09 02:17:27 +00:00
parent 87986384a7
commit 19b3dd0c42
2 changed files with 55 additions and 5 deletions
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22
lib/Transforms/IPO/DeadArgumentElimination.cpp
View File

@ -343,8 +343,9 @@ bool DAE::RemoveDeadArgumentsFromCallers(Function &Fn)
if (Fn.isDeclaration() || Fn.mayBeOverridden())
return false;
// Functions with local linkage should already have been handled.
if (Fn.hasLocalLinkage())
// Functions with local linkage should already have been handled, except the
// fragile (variadic) ones which we can improve here.
if (Fn.hasLocalLinkage() && !Fn.getFunctionType()->isVarArg())
return false;
if (Fn.use_empty())
@ -604,9 +605,20 @@ void DAE::SurveyFunction(const Function &F) {
UseVector MaybeLiveArgUses;
for (Function::const_arg_iterator AI = F.arg_begin(),
E = F.arg_end(); AI != E; ++AI, ++i) {
// See what the effect of this use is (recording any uses that cause
// MaybeLive in MaybeLiveArgUses).
Liveness Result = SurveyUses(AI, MaybeLiveArgUses);
Liveness Result;
if (F.getFunctionType()->isVarArg()) {
// Variadic functions will already have a va_arg function expanded inside
// them, making them potentially very sensitive to ABI changes resulting
// from removing arguments entirely, so don't. For example AArch64 handles
// register and stack HFAs very differently, and this is reflected in the
// IR which has already been generated.
Result = Live;
} else {
// See what the effect of this use is (recording any uses that cause
// MaybeLive in MaybeLiveArgUses).
Result = SurveyUses(AI, MaybeLiveArgUses);
}
// Mark the result.
MarkValue(CreateArg(&F, i), Result, MaybeLiveArgUses);
// Clear the vector again for the next iteration.

38
test/Transforms/DeadArgElim/variadic_safety.ll Normal file
View File

@ -0,0 +1,38 @@
; RUN: opt < %s -deadargelim -S | FileCheck %s
declare void @llvm.va_start(i8*)
define internal i32 @va_func(i32 %a, i32 %b, ...) {
%valist = alloca i8
call void @llvm.va_start(i8* %valist)
ret i32 %b
}
; Function derived from AArch64 ABI, where 8 integer arguments go in
; registers but the 9th goes on the stack. We really don't want to put
; just 7 args in registers and then start on the stack since any
; va_arg implementation already present in va_func won't be expecting
; it.
define i32 @call_va(i32 %in) {
%stacked = alloca i32
store i32 42, i32* %stacked
%res = call i32(i32, i32, ...)* @va_func(i32 %in, i32 %in, [6 x i32] undef, i32* byval %stacked)
ret i32 %res
; CHECK: call i32 (i32, i32, ...)* @va_func(i32 undef, i32 %in, [6 x i32] undef, i32* byval %stacked)
}
define internal i32 @va_deadret_func(i32 %a, i32 %b, ...) {
%valist = alloca i8
call void @llvm.va_start(i8* %valist)
ret i32 %a
}
define void @call_deadret(i32 %in) {
%stacked = alloca i32
store i32 42, i32* %stacked
call i32 (i32, i32, ...)* @va_deadret_func(i32 undef, i32 %in, [6 x i32] undef, i32* byval %stacked)
ret void
; CHECK: call void (i32, i32, ...)* @va_deadret_func(i32 undef, i32 undef, [6 x i32] undef, i32* byval %stacked)
}