[GlobalISel] Defer setting HasCalls on MachineFrameInfo to selection time.

We currently always set the HasCalls on MFI during translation and legalization if
we're handling a call or legalizing to a libcall. However, if that call is later
optimized to a tail call then we don't need the flag. The flag being set to true
causes frame lowering to always save and restore FP/LR, which adds unnecessary code.

This change does the same thing as SelectionDAG and ports over some code that scans
instructions after selection, using TargetInstrInfo to determine if target opcodes
are known calls.

Code size geomean improvements on CTMark:
 -O0 : 0.1%
 -Os : 0.3%

Differential Revision: https://reviews.llvm.org/D67868

llvm-svn: 372443

llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp

@@ -1564,7 +1564,9 @@ bool IRTranslator::translateCallSite(const ImmutableCallSite &CS,
     Args.push_back(getOrCreateVRegs(*Arg));
   }
 
-  MF->getFrameInfo().setHasCalls(true);
+  // We don't set HasCalls on MFI here yet because call lowering may decide to
+  // optimize into tail calls. Instead, we defer that to selection where a final
+  // scan is done to check if any instructions are calls.
   bool Success =
       CLI->lowerCall(MIRBuilder, CS, Res, Args, SwiftErrorVReg,
                      [&]() { return getOrCreateVReg(*CS.getCalledValue()); });

llvm/lib/CodeGen/GlobalISel/InstructionSelect.cpp

@@ -17,7 +17,9 @@
 #include "llvm/CodeGen/GlobalISel/LegalizerInfo.h"
 #include "llvm/CodeGen/GlobalISel/Utils.h"
 #include "llvm/CodeGen/MachineOptimizationRemarkEmitter.h"
+#include "llvm/CodeGen/MachineFrameInfo.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/CodeGen/TargetInstrInfo.h"
 #include "llvm/CodeGen/TargetLowering.h"
 #include "llvm/CodeGen/TargetPassConfig.h"
 #include "llvm/CodeGen/TargetSubtargetInfo.h"
@@ -223,6 +225,22 @@ bool InstructionSelect::runOnMachineFunction(MachineFunction &MF) {
   auto &TLI = *MF.getSubtarget().getTargetLowering();
   TLI.finalizeLowering(MF);
 
+  // Determine if there are any calls in this machine function. Ported from
+  // SelectionDAG.
+  MachineFrameInfo &MFI = MF.getFrameInfo();
+  for (const auto &MBB : MF) {
+    if (MFI.hasCalls() && MF.hasInlineAsm())
+      break;
+
+    for (const auto &MI : MBB) {
+      if ((MI.isCall() && !MI.isReturn()) || MI.isStackAligningInlineAsm())
+        MFI.setHasCalls(true);
+      if (MI.isInlineAsm())
+        MF.setHasInlineAsm(true);
+    }
+  }
+
+
   LLVM_DEBUG({
     dbgs() << "Rules covered by selecting function: " << MF.getName() << ":";
     for (auto RuleID : CoverageInfo.covered())

llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp

@@ -364,8 +364,6 @@ llvm::createLibcall(MachineIRBuilder &MIRBuilder, RTLIB::Libcall Libcall,
   auto &TLI = *MIRBuilder.getMF().getSubtarget().getTargetLowering();
   const char *Name = TLI.getLibcallName(Libcall);
 
-  MIRBuilder.getMF().getFrameInfo().setHasCalls(true);
-
   CallLowering::CallLoweringInfo Info;
   Info.CallConv = TLI.getLibcallCallingConv(Libcall);
   Info.Callee = MachineOperand::CreateES(Name);
@@ -430,7 +428,6 @@ llvm::createMemLibcall(MachineIRBuilder &MIRBuilder, MachineRegisterInfo &MRI,
   const char *Name = TLI.getLibcallName(RTLibcall);
 
   MIRBuilder.setInstr(MI);
-  MIRBuilder.getMF().getFrameInfo().setHasCalls(true);
 
   CallLowering::CallLoweringInfo Info;
   Info.CallConv = TLI.getLibcallCallingConv(RTLibcall);

llvm/test/CodeGen/AArch64/GlobalISel/call-translator.ll

@@ -100,7 +100,6 @@ define {double, i64, i32} @test_struct_return({double, i64, i32}* %addr) {
 }
 
 ; CHECK-LABEL: name: test_arr_call
-; CHECK: hasCalls: true
 ; CHECK: %0:_(p0) = COPY $x0
 ; CHECK: [[LD1:%[0-9]+]]:_(s64) = G_LOAD %0(p0) :: (load 8 from %ir.addr)
 ; CHECK: [[CST1:%[0-9]+]]:_(s64) = G_CONSTANT i64 8

llvm/test/CodeGen/AArch64/GlobalISel/tail-call-no-save-fp-lr.ll

@@ -0,0 +1,20 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc %s -verify-machineinstrs -mtriple aarch64-apple-darwin -global-isel -global-isel-abort=1 -o - 2>&1 | FileCheck %s
+
+; Check that we get a tail call to foo without saving fp/lr.
+define void @bar(i32 %a) #1 {
+; CHECK-LABEL: bar:
+; CHECK:       ; %bb.0: ; %entry
+; CHECK-NEXT:    b _zoo
+entry:
+  tail call void @zoo(i32 undef)
+  ret void
+}
+
+define void @zoo(i32 %a) {
+entry:
+  ret void
+}
+
+attributes #1 = { "frame-pointer"="all" }
+