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X86: Align the stack on word boundaries in LowerFormalArguments() 

The goal of the patch is to implement section 3.2.3 of the AMD64 ABI
correctly.  The controlling sentence is, "The size of each argument gets
rounded up to eightbytes.  Therefore the stack will always be eightbyte
aligned." The equivalent sentence in the i386 ABI page 37 says, "At all
times, the stack pointer should point to a word-aligned area."  For both
architectures, the stack pointer is not being rounded up to the nearest
eightbyte or word between the last normal argument and the first
variadic argument.

Patch by Thomas Jablin!

llvm-svn: 216119
This commit is contained in:
Duncan P. N. Exon Smith 2014-08-20 19:40:59 +00:00
parent 8968e6d1b0
commit b18263531d
3 changed files with 38 additions and 2 deletions
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9
llvm/include/llvm/CodeGen/CallingConvLower.h
View File

@ -371,11 +371,16 @@ public:
return Reg;
}
/// AlignStack - Align the top of the stakc to the specified alignment.
void AlignStack(unsigned Align) {
assert(Align && ((Align - 1) & Align) == 0); // Align is power of 2.
StackOffset = ((StackOffset + Align - 1) & ~(Align - 1));
}
/// AllocateStack - Allocate a chunk of stack space with the specified size
/// and alignment.
unsigned AllocateStack(unsigned Size, unsigned Align) {
assert(Align && ((Align-1) & Align) == 0); // Align is power of 2.
StackOffset = ((StackOffset + Align-1) & ~(Align-1));
AlignStack(Align);
unsigned Result = StackOffset;
StackOffset += Size;
MF.getFrameInfo()->ensureMaxAlignment(Align);

1
llvm/lib/Target/X86/X86ISelLowering.cpp
View File

@ -2300,6 +2300,7 @@ X86TargetLowering::LowerFormalArguments(SDValue Chain,
CCInfo.AllocateStack(32, 8);
CCInfo.AnalyzeFormalArguments(Ins, CC_X86);
CCInfo.AlignStack(Is64Bit ? 8 : 4);
unsigned LastVal = ~0U;
SDValue ArgValue;

30
llvm/test/CodeGen/X86/aligned-variadic.ll Normal file
View File

@ -0,0 +1,30 @@
; RUN: llc < %s -march=x86-64 | FileCheck %s -check-prefix=X64
; RUN: llc < %s -march=x86 | FileCheck %s -check-prefix=X32
%struct.Baz = type { [17 x i8] }
%struct.__va_list_tag = type { i32, i32, i8*, i8* }
; Function Attrs: nounwind uwtable
define void @bar(%struct.Baz* byval nocapture readnone align 8 %x, ...) {
entry:
%va = alloca [1 x %struct.__va_list_tag], align 16
%arraydecay = getelementptr inbounds [1 x %struct.__va_list_tag]* %va, i64 0, i64 0
%arraydecay1 = bitcast [1 x %struct.__va_list_tag]* %va to i8*
call void @llvm.va_start(i8* %arraydecay1)
%overflow_arg_area_p = getelementptr inbounds [1 x %struct.__va_list_tag]* %va, i64 0, i64 0, i32 2
%overflow_arg_area = load i8** %overflow_arg_area_p, align 8
%overflow_arg_area.next = getelementptr i8* %overflow_arg_area, i64 24
store i8* %overflow_arg_area.next, i8** %overflow_arg_area_p, align 8
; X32: leal 68(%esp), [[REG:%.*]]
; X32: movl [[REG]], 16(%esp)
; X64: leaq 232(%rsp), [[REG:%.*]]
; X64: movq [[REG]], 184(%rsp)
; X64: leaq 176(%rsp), %rdi
call void @qux(%struct.__va_list_tag* %arraydecay)
ret void
}
; Function Attrs: nounwind
declare void @llvm.va_start(i8*)
declare void @qux(%struct.__va_list_tag*)