[PATCH] D64986: [IPRA][ARM] Make use of the "returned" parameter attribute

[Oliver Stannard (Linaro) via Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rL366669: [IPRA][ARM] Make use of the "returned" parameter attribute (authored by ostannard, committed by ).

Changed prior to commit:
  https://reviews.llvm.org/D64986?vs=210797&id=211028#toc

Repository:
  rL LLVM

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D64986/new/

https://reviews.llvm.org/D64986

Files:
  llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
  llvm/trunk/lib/Target/ARM/ARMFrameLowering.cpp
  llvm/trunk/lib/Target/ARM/ARMISelLowering.cpp
  llvm/trunk/lib/Target/ARM/ARMMachineFunctionInfo.h
  llvm/trunk/test/CodeGen/ARM/ipra-r0-returned.ll


Index: llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
===================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -9615,6 +9615,8 @@
       Flags.setOrigAlign(OriginalAlignment);
       if (ArgCopyElisionCandidates.count(&Arg))
         Flags.setCopyElisionCandidate();
+      if (Arg.hasAttribute(Attribute::Returned))
+        Flags.setReturned();
 
       MVT RegisterVT = TLI->getRegisterTypeForCallingConv(
           *CurDAG->getContext(), F.getCallingConv(), VT);
Index: llvm/trunk/lib/Target/ARM/ARMMachineFunctionInfo.h
===================================================================
--- llvm/trunk/lib/Target/ARM/ARMMachineFunctionInfo.h
+++ llvm/trunk/lib/Target/ARM/ARMMachineFunctionInfo.h
@@ -130,6 +130,10 @@
   /// The amount the literal pool has been increasedby due to promoted globals.
   int PromotedGlobalsIncrease = 0;
 
+  /// True if r0 will be preserved by a call to this function (e.g. C++
+  /// con/destructors).
+  bool PreservesR0 = false;
+
 public:
   ARMFunctionInfo() = default;
 
@@ -247,6 +251,9 @@
   }
 
   DenseMap<unsigned, unsigned> EHPrologueRemappedRegs;
+
+  void setPreservesR0() { PreservesR0 = true; }
+  bool getPreservesR0() const { return PreservesR0; }
 };
 
 } // end namespace llvm
Index: llvm/trunk/lib/Target/ARM/ARMFrameLowering.cpp
===================================================================
--- llvm/trunk/lib/Target/ARM/ARMFrameLowering.cpp
+++ llvm/trunk/lib/Target/ARM/ARMFrameLowering.cpp
@@ -2097,6 +2097,12 @@
     AFI->setLRIsSpilledForFarJump(true);
   }
   AFI->setLRIsSpilled(SavedRegs.test(ARM::LR));
+
+  // If we have the "returned" parameter attribute which guarantees that we
+  // return the value which was passed in r0 unmodified (e.g. C++ 'structors),
+  // record that fact for IPRA.
+  if (AFI->getPreservesR0())
+    SavedRegs.set(ARM::R0);
 }
 
 MachineBasicBlock::iterator ARMFrameLowering::eliminateCallFramePseudoInstr(
Index: llvm/trunk/lib/Target/ARM/ARMISelLowering.cpp
===================================================================
--- llvm/trunk/lib/Target/ARM/ARMISelLowering.cpp
+++ llvm/trunk/lib/Target/ARM/ARMISelLowering.cpp
@@ -3898,6 +3898,12 @@
         // Transform the arguments in physical registers into virtual ones.
         unsigned Reg = MF.addLiveIn(VA.getLocReg(), RC);
         ArgValue = DAG.getCopyFromReg(Chain, dl, Reg, RegVT);
+
+        // If this value is passed in r0 and has the returned attribute (e.g.
+        // C++ 'structors), record this fact for later use.
+        if (VA.getLocReg() == ARM::R0 && Ins[VA.getValNo()].Flags.isReturned()) {
+          AFI->setPreservesR0();
+        }
       }
 
       // If this is an 8 or 16-bit value, it is really passed promoted
Index: llvm/trunk/test/CodeGen/ARM/ipra-r0-returned.ll
===================================================================
--- llvm/trunk/test/CodeGen/ARM/ipra-r0-returned.ll
+++ llvm/trunk/test/CodeGen/ARM/ipra-r0-returned.ll
@@ -0,0 +1,18 @@
+; RUN: llc -mtriple armv7a--none-eabi -enable-ipra=false < %s | FileCheck %s
+; RUN: llc -mtriple armv7a--none-eabi -enable-ipra=true  < %s | FileCheck %s
+
+define i32 @returns_r0(i32 returned %a)  {
+entry:
+  call void asm sideeffect "", "~{r0}"()
+  ret i32 %a
+}
+
+define i32 @test(i32 %a) {
+; CHECK-LABEL: test:
+entry:
+; CHECK-NOT: r0
+; CHECK: bl      returns_r0
+; CHECK-NOT: r0
+  %b = call i32 @returns_r0(i32 %a)
+  ret i32 %a
+}


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