[llvm] r265886 - [CodeGen] Don't assume that fixed stack objects are aligned in a stack-realigned function.
Charles Davis via llvm-commits
llvm-commits at lists.llvm.org
Sat Apr 9 16:34:43 PDT 2016
Author: cdavis
Date: Sat Apr 9 18:34:42 2016
New Revision: 265886
URL: http://llvm.org/viewvc/llvm-project?rev=265886&view=rev
Log:
[CodeGen] Don't assume that fixed stack objects are aligned in a stack-realigned function.
Summary:
After we make the adjustment, we can assume that for local allocas, but
not for stack parameters, the return address, or any other fixed stack
object (which has a negative offset and therefore lies prior to the
adjusted SP).
Fixes PR26662.
Reviewers: hfinkel, qcolombet, rnk
Subscribers: rnk, llvm-commits
Differential Revision: http://reviews.llvm.org/D18471
Modified:
llvm/trunk/include/llvm/CodeGen/MachineFrameInfo.h
llvm/trunk/lib/CodeGen/MachineFunction.cpp
llvm/trunk/test/CodeGen/X86/stack-align.ll
Modified: llvm/trunk/include/llvm/CodeGen/MachineFrameInfo.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/CodeGen/MachineFrameInfo.h?rev=265886&r1=265885&r2=265886&view=diff
==============================================================================
--- llvm/trunk/include/llvm/CodeGen/MachineFrameInfo.h (original)
+++ llvm/trunk/include/llvm/CodeGen/MachineFrameInfo.h Sat Apr 9 18:34:42 2016
@@ -253,6 +253,9 @@ class MachineFrameInfo {
/// Whether the "realign-stack" option is on.
bool RealignOption;
+ /// Whether the function has the \c alignstack attribute.
+ bool ForcedRealign;
+
/// True if the function dynamically adjusts the stack pointer through some
/// opaque mechanism like inline assembly or Win32 EH.
bool HasOpaqueSPAdjustment;
@@ -279,9 +282,9 @@ class MachineFrameInfo {
public:
explicit MachineFrameInfo(unsigned StackAlign, bool isStackRealign,
- bool RealignOpt)
+ bool RealignOpt, bool ForceRealign)
: StackAlignment(StackAlign), StackRealignable(isStackRealign),
- RealignOption(RealignOpt) {
+ RealignOption(RealignOpt), ForcedRealign(ForceRealign) {
StackSize = NumFixedObjects = OffsetAdjustment = MaxAlignment = 0;
HasVarSizedObjects = false;
FrameAddressTaken = false;
Modified: llvm/trunk/lib/CodeGen/MachineFunction.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/MachineFunction.cpp?rev=265886&r1=265885&r2=265886&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/MachineFunction.cpp (original)
+++ llvm/trunk/lib/CodeGen/MachineFunction.cpp Sat Apr 9 18:34:42 2016
@@ -84,6 +84,13 @@ void ilist_traits<MachineBasicBlock>::de
MBB->getParent()->DeleteMachineBasicBlock(MBB);
}
+static inline unsigned getFnStackAlignment(const TargetSubtargetInfo *STI,
+ const Function *Fn) {
+ if (Fn->hasFnAttribute(Attribute::StackAlignment))
+ return Fn->getFnStackAlignment();
+ return STI->getFrameLowering()->getStackAlignment();
+}
+
MachineFunction::MachineFunction(const Function *F, const TargetMachine &TM,
unsigned FunctionNum, MachineModuleInfo &mmi)
: Fn(F), Target(TM), STI(TM.getSubtargetImpl(*F)), Ctx(mmi.getContext()),
@@ -97,9 +104,11 @@ MachineFunction::MachineFunction(const F
MFInfo = nullptr;
FrameInfo = new (Allocator)
- MachineFrameInfo(STI->getFrameLowering()->getStackAlignment(),
+ MachineFrameInfo(getFnStackAlignment(STI, Fn),
STI->getFrameLowering()->isStackRealignable(),
- !F->hasFnAttribute("no-realign-stack"));
+ !F->hasFnAttribute("no-realign-stack"),
+ !F->hasFnAttribute("no-realign-stack") &&
+ F->hasFnAttribute(Attribute::StackAlignment));
if (Fn->hasFnAttribute(Attribute::StackAlignment))
FrameInfo->ensureMaxAlignment(Fn->getFnStackAlignment());
@@ -613,8 +622,10 @@ int MachineFrameInfo::CreateFixedObject(
// The alignment of the frame index can be determined from its offset from
// the incoming frame position. If the frame object is at offset 32 and
// the stack is guaranteed to be 16-byte aligned, then we know that the
- // object is 16-byte aligned.
- unsigned Align = MinAlign(SPOffset, StackAlignment);
+ // object is 16-byte aligned. Note that unlike the non-fixed case, if the
+ // stack needs realignment, we can't assume that the stack will in fact be
+ // aligned.
+ unsigned Align = MinAlign(SPOffset, ForcedRealign ? 1 : StackAlignment);
Align = clampStackAlignment(!StackRealignable || !RealignOption, Align,
StackAlignment);
Objects.insert(Objects.begin(), StackObject(Size, Align, SPOffset, Immutable,
@@ -627,7 +638,7 @@ int MachineFrameInfo::CreateFixedObject(
/// Returns an index with a negative value.
int MachineFrameInfo::CreateFixedSpillStackObject(uint64_t Size,
int64_t SPOffset) {
- unsigned Align = MinAlign(SPOffset, StackAlignment);
+ unsigned Align = MinAlign(SPOffset, ForcedRealign ? 1 : StackAlignment);
Align = clampStackAlignment(!StackRealignable || !RealignOption, Align,
StackAlignment);
Objects.insert(Objects.begin(), StackObject(Size, Align, SPOffset,
Modified: llvm/trunk/test/CodeGen/X86/stack-align.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/stack-align.ll?rev=265886&r1=265885&r2=265886&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/X86/stack-align.ll (original)
+++ llvm/trunk/test/CodeGen/X86/stack-align.ll Sat Apr 9 18:34:42 2016
@@ -61,3 +61,31 @@ entry:
; CHECK-NOT: and
; CHECK: ret
}
+
+%struct.sixteen = type { [16 x i8] }
+
+; Accessing stack parameters shouldn't assume stack alignment. Here we should
+; emit two 8-byte loads, followed by two 8-byte stores.
+define x86_stdcallcc void @test5(%struct.sixteen* byval nocapture readonly align 4 %s) #0 {
+ %d.sroa.0 = alloca [16 x i8], align 1
+ %1 = getelementptr inbounds [16 x i8], [16 x i8]* %d.sroa.0, i32 0, i32 0
+ call void @llvm.lifetime.start(i64 16, i8* %1)
+ %2 = getelementptr inbounds %struct.sixteen, %struct.sixteen* %s, i32 0, i32 0, i32 0
+ call void @llvm.memcpy.p0i8.p0i8.i32(i8* %1, i8* %2, i32 16, i32 1, i1 true)
+ call void @llvm.lifetime.end(i64 16, i8* %1)
+ ret void
+; CHECK-LABEL: test5:
+; CHECK: and
+; CHECK: movsd
+; CHECK-NEXT: movsd
+; CHECK-NEXT: movsd
+; CHECK-NEXT: movsd
+}
+
+declare void @llvm.lifetime.start(i64, i8* nocapture) argmemonly nounwind
+
+declare void @llvm.memcpy.p0i8.p0i8.i32(i8* nocapture, i8* nocapture readonly, i32, i32, i1) argmemonly nounwind
+
+declare void @llvm.lifetime.end(i64, i8* nocapture) argmemonly nounwind
+
+attributes #0 = { nounwind alignstack=16 "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" }
More information about the llvm-commits
mailing list