[mips] Support `long_call/far/near` attributes passed by front-end

[atanasyan]

Summary

This patch adds handling of the long_call, far, and near attributes passed by front-end. The patch depends on D35479.

[sdardis]

Some minor nits. Also, see my question inline.

lib/Target/Mips/MipsISelLowering.cpp

3156

Restore the comment from lines 3156-3157 to an appropriate place.

Question (I haven't looked throughly yet): Can an ExternalSymbolSDNode have the long-call/near-call attribute?

If it can, then this expansion code is missing the portions that check the attributes of the ExternalSymbolSDNode.

test/CodeGen/Mips/long-call-attr.ll

5

Also requires testing for mips64.

15

; CHECK-LABEL: foo: before this.

[atanasyan]

lib/Target/Mips/MipsISelLowering.cpp

3156

Can an ExternalSymbolSDNode have the long-call/near-call attribute?

As far as I understand the IR, ExternalSymbolSDNode cannot contains any attribute.

[atanasyan]

• Addressed review comments: add 64-bit tests, restore comment in the code.

[sdardis]

LGTM.

[atanasyan]

Closed by commit rL308606

lib/Target/Mips/MipsISelLowering.cpp

MipsTargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
 
   SDValue CalleeLo;
   EVT Ty = Callee.getValueType();
   bool GlobalOrExternal = false, IsCallReloc = false;
 
   // The long-calls feature is ignored in case of PIC.
   // While we do not support -mshared / -mno-shared properly,
   // ignore long-calls in case of -mabicalls too.
-  if (Subtarget.useLongCalls() && !Subtarget.isABICalls() && !IsPIC) {
-    // Get the address of the callee into a register to prevent
-    // using of the `jal` instruction for the direct call.
-    if (auto *N = dyn_cast<GlobalAddressSDNode>(Callee))
-      Callee = Subtarget.hasSym32() ? getAddrNonPIC(N, SDLoc(N), Ty, DAG)
-                                    : getAddrNonPICSym64(N, SDLoc(N), Ty, DAG);
-    else if (auto *N = dyn_cast<ExternalSymbolSDNode>(Callee))
-      Callee = Subtarget.hasSym32() ? getAddrNonPIC(N, SDLoc(N), Ty, DAG)
-                                    : getAddrNonPICSym64(N, SDLoc(N), Ty, DAG);
+  if (!Subtarget.isABICalls() && !IsPIC) {
+    if (auto *N = dyn_cast<ExternalSymbolSDNode>(Callee)) {
+      if (Subtarget.useLongCalls())
+        Callee = Subtarget.hasSym32()
+                     ? getAddrNonPIC(N, SDLoc(N), Ty, DAG)
+    } else if (auto *N = dyn_cast<GlobalAddressSDNode>(Callee)) {
+      bool UseLongCalls = Subtarget.useLongCalls();
+      // If the function has long-call/far/near attribute
+      // it overrides command line switch pased to the backend.
+      if (auto *F = dyn_cast<Function>(N->getGlobal())) {
+        if (F->hasFnAttribute("long-call"))
+          UseLongCalls = true;
+        else if (F->hasFnAttribute("near-call"))
+          UseLongCalls = false;
+      }
+      if (UseLongCalls)
+        Callee = Subtarget.hasSym32()
+                     ? getAddrNonPIC(N, SDLoc(N), Ty, DAG)
     }
+  }
 
   if (GlobalAddressSDNode *G = dyn_cast<GlobalAddressSDNode>(Callee)) {
     if (IsPIC) {
       const GlobalValue *Val = G->getGlobal();
       InternalLinkage = Val->hasInternalLinkage();
 
       if (InternalLinkage)
         Callee = getAddrLocal(G, DL, Ty, DAG, ABI.IsN32() || ABI.IsN64());

test/CodeGen/Mips/long-call-attr.ll

+; RUN: llc -march=mips -mcpu=mips32 --mattr=+long-calls,+noabicalls < %s \
+; RUN:   | FileCheck %s
+; RUN: llc -march=mips -mcpu=mips32 --mattr=-long-calls,+noabicalls < %s \
+; RUN:   | FileCheck %s
+
+declare void @far() #0
+
+define void @near() #1 {
+  ret void
+}
+
+define void @foo() #2 {
+  call void @far() #3
+
+; CHECK:      lui     $1, %hi(far)
+; CHECK-NEXT: addiu   $25, $1, %lo(far)
+; CHECK-NEXT: jalr    $25
+
+  call void @near() #4
+
+; CHECK:      jal near
+
+  ret void
+}
+
+attributes #0 = { "long-call" }
+attributes #1 = { noinline nounwind "near-call" }
+attributes #2 = { noinline nounwind }
+attributes #3 = { "long-call" }
+attributes #4 = { "near-call" }