[Stack realignment] Handling of aligned allocas.

This patch implements dynamic realignment of stack objects for targets
with a non-realigned stack pointer. Behaviour in FunctionLoweringInfo
is changed so that for a target that has StackRealignable set to
false, over-aligned static allocas are considered to be variable-sized
objects and are handled with DYNAMIC_STACKALLOC nodes.

It would be good to group aligned allocas into a single big alloca as
an optimization, but this is yet todo.

SystemZ benefits from this, due to its stack frame layout.

New tests SystemZ/alloca-03.ll for aligned allocas, and
SystemZ/alloca-04.ll for "no-realign-stack" attribute on functions.

Review and help from Ulrich Weigand and Hal Finkel.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@254227 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/llvm/CodeGen/MachineFrameInfo.h b/include/llvm/CodeGen/MachineFrameInfo.h
index f95cbdb49aff438c47f4faa8bd292429b7472cf1..f5a688458d2e65621aa7b36b34101d70d6ede0bc 100644 (file)
--- a/include/llvm/CodeGen/MachineFrameInfo.h
+++ b/include/llvm/CodeGen/MachineFrameInfo.h
@@ -125,6 +125,16 @@ class MachineFrameInfo {
   unsigned StackAlignment;
 
   /// Can the stack be realigned.
+  /// Targets that set this to false don't have the ability to overalign
+  /// their stack frame, and thus, overaligned allocas are all treated
+  /// as dynamic allocations and the target must handle them as part
+  /// of DYNAMIC_STACKALLOC lowering.
+  /// FIXME: There is room for improvement in this case, in terms of
+  /// grouping overaligned allocas into a "secondary stack frame" and
+  /// then only use a single alloca to allocate this frame and only a
+  /// single virtual register to access it. Currently, without such an
+  /// optimization, each such alloca gets it's own dynamic
+  /// realignment.
   bool StackRealignable;
 
   /// The list of stack objects allocated.

diff --git a/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp b/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp
index 8d42dcef14015802f39b930958f9d04df8b66dfb..ff0ccd415db43159f4769baf6871a5a2c8cd46cd 100644 (file)
--- a/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp
+++ b/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp
@@ -87,6 +87,7 @@ void FunctionLoweringInfo::set(const Function &fn, MachineFunction &mf,
   TLI = MF->getSubtarget().getTargetLowering();
   RegInfo = &MF->getRegInfo();
   MachineModuleInfo &MMI = MF->getMMI();
+  const TargetFrameLowering *TFI = MF->getSubtarget().getFrameLowering();
 
   // Check whether the function can return without sret-demotion.
   SmallVector<ISD::OutputArg, 4> Outs;
@@ -103,28 +104,29 @@ void FunctionLoweringInfo::set(const Function &fn, MachineFunction &mf,
     for (BasicBlock::const_iterator I = BB->begin(), E = BB->end();
          I != E; ++I) {
       if (const AllocaInst *AI = dyn_cast<AllocaInst>(I)) {
-        // Static allocas can be folded into the initial stack frame adjustment.
-        if (AI->isStaticAlloca()) {
+        Type *Ty = AI->getAllocatedType();
+        unsigned Align =
+          std::max((unsigned)MF->getDataLayout().getPrefTypeAlignment(Ty),
+                   AI->getAlignment());
+        unsigned StackAlign = TFI->getStackAlignment();
+
+        // Static allocas can be folded into the initial stack frame
+        // adjustment. For targets that don't realign the stack, don't
+        // do this if there is an extra alignment requirement.
+        if (AI->isStaticAlloca() && 
+            (TFI->isStackRealignable() || (Align <= StackAlign))) {
           const ConstantInt *CUI = cast<ConstantInt>(AI->getArraySize());
-          Type *Ty = AI->getAllocatedType();
           uint64_t TySize = MF->getDataLayout().getTypeAllocSize(Ty);
-          unsigned Align =
-              std::max((unsigned)MF->getDataLayout().getPrefTypeAlignment(Ty),
-                       AI->getAlignment());
 
           TySize *= CUI->getZExtValue();   // Get total allocated size.
           if (TySize == 0) TySize = 1; // Don't create zero-sized stack objects.
 
           StaticAllocaMap[AI] =
             MF->getFrameInfo()->CreateStackObject(TySize, Align, false, AI);
-
         } else {
-          unsigned Align =
-              std::max((unsigned)MF->getDataLayout().getPrefTypeAlignment(
-                           AI->getAllocatedType()),
-                       AI->getAlignment());
-          unsigned StackAlign =
-              MF->getSubtarget().getFrameLowering()->getStackAlignment();
+          // FIXME: Overaligned static allocas should be grouped into
+          // a single dynamic allocation instead of using a separate
+          // stack allocation for each one.
           if (Align <= StackAlign)
             Align = 0;
           // Inform the Frame Information that we have variable-sized objects.

diff --git a/lib/Target/SystemZ/SystemZFrameLowering.cpp b/lib/Target/SystemZ/SystemZFrameLowering.cpp
index 9eeb046644612dd32b72e41ef2e573de73f780c8..e1b20d0536d12e99680b60c7707434a462912627 100644 (file)
--- a/lib/Target/SystemZ/SystemZFrameLowering.cpp
+++ b/lib/Target/SystemZ/SystemZFrameLowering.cpp
@@ -48,7 +48,8 @@ static const TargetFrameLowering::SpillSlot SpillOffsetTable[] = {
 
 SystemZFrameLowering::SystemZFrameLowering()
     : TargetFrameLowering(TargetFrameLowering::StackGrowsDown, 8,
-                          -SystemZMC::CallFrameSize, 8) {
+                          -SystemZMC::CallFrameSize, 8,
+                          false /* StackRealignable */) {
   // Create a mapping from register number to save slot offset.
   RegSpillOffsets.grow(SystemZ::NUM_TARGET_REGS);
   for (unsigned I = 0, E = array_lengthof(SpillOffsetTable); I != E; ++I)

diff --git a/lib/Target/SystemZ/SystemZISelLowering.cpp b/lib/Target/SystemZ/SystemZISelLowering.cpp
index fa9ee6e2eebb3bb74d821d5c6e2e889cb1e9766c..5959e90d2f626b8b797371b3f7a30d0b83ba3fd3 100644 (file)
--- a/lib/Target/SystemZ/SystemZISelLowering.cpp
+++ b/lib/Target/SystemZ/SystemZISelLowering.cpp
@@ -2739,17 +2739,37 @@ SDValue SystemZTargetLowering::lowerVACOPY(SDValue Op,
 
 SDValue SystemZTargetLowering::
 lowerDYNAMIC_STACKALLOC(SDValue Op, SelectionDAG &DAG) const {
+  const TargetFrameLowering *TFI = Subtarget.getFrameLowering();
+  bool RealignOpt = !DAG.getMachineFunction().getFunction()->
+    hasFnAttribute("no-realign-stack");
+
   SDValue Chain = Op.getOperand(0);
   SDValue Size  = Op.getOperand(1);
+  SDValue Align = Op.getOperand(2);
   SDLoc DL(Op);
 
+  // If user has set the no alignment function attribute, ignore
+  // alloca alignments.
+  uint64_t AlignVal = (RealignOpt ?
+                       dyn_cast<ConstantSDNode>(Align)->getZExtValue() : 0);
+
+  uint64_t StackAlign = TFI->getStackAlignment();
+  uint64_t RequiredAlign = std::max(AlignVal, StackAlign);
+  uint64_t ExtraAlignSpace = RequiredAlign - StackAlign;
+
   unsigned SPReg = getStackPointerRegisterToSaveRestore();
+  SDValue NeededSpace = Size;
 
   // Get a reference to the stack pointer.
   SDValue OldSP = DAG.getCopyFromReg(Chain, DL, SPReg, MVT::i64);
 
+  // Add extra space for alignment if needed.
+  if (ExtraAlignSpace)
+    NeededSpace = DAG.getNode(ISD::ADD, DL, MVT::i64, NeededSpace,
+                              DAG.getConstant(ExtraAlignSpace, DL, MVT::i64)); 
+
   // Get the new stack pointer value.
-  SDValue NewSP = DAG.getNode(ISD::SUB, DL, MVT::i64, OldSP, Size);
+  SDValue NewSP = DAG.getNode(ISD::SUB, DL, MVT::i64, OldSP, NeededSpace);
 
   // Copy the new stack pointer back.
   Chain = DAG.getCopyToReg(Chain, DL, SPReg, NewSP);
@@ -2760,6 +2780,16 @@ lowerDYNAMIC_STACKALLOC(SDValue Op, SelectionDAG &DAG) const {
   SDValue ArgAdjust = DAG.getNode(SystemZISD::ADJDYNALLOC, DL, MVT::i64);
   SDValue Result = DAG.getNode(ISD::ADD, DL, MVT::i64, NewSP, ArgAdjust);
 
+  // Dynamically realign if needed.
+  if (RequiredAlign > StackAlign) {
+    Result =
+      DAG.getNode(ISD::ADD, DL, MVT::i64, Result,
+                  DAG.getConstant(ExtraAlignSpace, DL, MVT::i64));
+    Result =
+      DAG.getNode(ISD::AND, DL, MVT::i64, Result,
+                  DAG.getConstant(~(RequiredAlign - 1), DL, MVT::i64));
+  }
+
   SDValue Ops[2] = { Result, Chain };
   return DAG.getMergeValues(Ops, DL);
 }

diff --git a/test/CodeGen/SystemZ/alloca-03.ll b/test/CodeGen/SystemZ/alloca-03.ll
new file mode 100644 (file)
index 0000000..ece1198
--- /dev/null
+++ b/test/CodeGen/SystemZ/alloca-03.ll
@@ -0,0 +1,84 @@
+; RUN: llc < %s -mtriple=s390x-linux-gnu | FileCheck %s
+
+; Allocate 8 bytes, no need to align stack.
+define void @f0() {
+; CHECK-LABEL: f0:
+; CHECK: aghi %r15, -168
+; CHECK-NOT: nil
+; CHECK: mvghi 160(%r15), 10
+; CHECK: aghi %r15, 168
+  %x = alloca i64
+  store volatile i64 10, i64* %x
+  ret void
+}
+
+; Allocate %len * 8, no need to align stack.
+define void @f1(i64 %len) {
+; CHECK-LABEL: f1:
+; CHECK: sllg    %r0, %r2, 3
+; CHECK: lgr     %r1, %r15
+; CHECK: sgr     %r1, %r0
+; CHECK-NOT: ngr
+; CHECK: lgr     %r15, %r1
+; CHECK: la      %r1, 160(%r1)
+; CHECK: mvghi   0(%r1), 10
+  %x = alloca i64, i64 %len
+  store volatile i64 10, i64* %x
+  ret void
+}
+
+; Static alloca, align 128.
+define void @f2() {
+; CHECK-LABEL: f2:
+; CHECK: aghi    %r1, -128
+; CHECK: lgr     %r15, %r1
+; CHECK: la      %r1, 280(%r1)
+; CHECK: nill   %r1, 65408
+; CHECK: mvghi   0(%r1), 10
+  %x = alloca i64, i64 1, align 128
+  store volatile i64 10, i64* %x, align 128
+  ret void
+}
+
+; Dynamic alloca, align 128.
+define void @f3(i64 %len) {
+; CHECK-LABEL: f3:
+; CHECK: sllg  %r1, %r2, 3
+; CHECK: la    %r0, 120(%r1)
+; CHECK: lgr   %r1, %r15
+; CHECK: sgr   %r1, %r0
+; CHECK: lgr   %r15, %r1
+; CHECK: la    %r1, 280(%r1)
+; CHECK: nill  %r1, 65408
+; CHECK: mvghi 0(%r1), 10
+  %x = alloca i64, i64 %len, align 128
+  store volatile i64 10, i64* %x, align 128
+  ret void
+}
+
+; Static alloca w/out alignment - part of frame.
+define void @f4() {
+; CHECK-LABEL: f4:
+; CHECK: aghi    %r15, -168
+; CHECK: mvhi    164(%r15), 10
+; CHECK: aghi    %r15, 168
+  %x = alloca i32
+  store volatile i32 10, i32* %x
+  ret void
+}
+
+; Static alloca of one i32, aligned by 128.
+define void @f5() {
+; CHECK-LABEL: f5:
+
+; CHECK: lgr   %r1, %r15
+; CHECK: aghi  %r1, -128
+; CHECK: lgr   %r15, %r1
+; CHECK: la    %r1, 280(%r1)
+; CHECK: nill  %r1, 65408
+; CHECK: mvhi  0(%r1), 10
+  %x = alloca i32, i64 1, align 128
+  store volatile i32 10, i32* %x
+  ret void
+}
+

diff --git a/test/CodeGen/SystemZ/alloca-04.ll b/test/CodeGen/SystemZ/alloca-04.ll
new file mode 100644 (file)
index 0000000..c7ecf38
--- /dev/null
+++ b/test/CodeGen/SystemZ/alloca-04.ll
@@ -0,0 +1,14 @@
+; Check the "no-realign-stack" function attribute. We should get a warning.
+
+; RUN: llc < %s -mtriple=s390x-linux-gnu -debug-only=codegen 2>&1 | \
+; RUN:   FileCheck %s
+
+
+define void @f6() "no-realign-stack" {
+  %x = alloca i64, i64 1, align 128
+  store volatile i64 10, i64* %x, align 128
+  ret void
+}
+
+; CHECK: Warning: requested alignment 128 exceeds the stack alignment 8
+; CHECK-NOT: nill