[PATCH] D73699: [RISCV] Implement mayBeEmittedAsTailCall for tail call optimization

[weiwei via Phabricator via llvm-commits]

wwei created this revision.
wwei added reviewers: asb, lenary, simoncook, edward-jones, lewis-revill.
wwei added a project: LLVM.
Herald added subscribers: llvm-commits, luismarques, apazos, sameer.abuasal, pzheng, s.egerton, Jim, benna, psnobl, jocewei, PkmX, rkruppe, the_o, brucehoult, MartinMosbeck, rogfer01, zzheng, MaskRay, jrtc27, shiva0217, kito-cheng, niosHD, sabuasal, johnrusso, rbar, hiraditya.

Implement TargetLowering callback `mayBeEmittedAsTailCall` for riscv in CodeGenPrepare,
which will duplicate return instructions to enable tailcall optimization.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D73699

Files:
  llvm/lib/Target/RISCV/RISCVISelLowering.cpp
  llvm/lib/Target/RISCV/RISCVISelLowering.h
  llvm/test/CodeGen/RISCV/tail-calls.ll


Index: llvm/test/CodeGen/RISCV/tail-calls.ll
===================================================================
--- llvm/test/CodeGen/RISCV/tail-calls.ll
+++ llvm/test/CodeGen/RISCV/tail-calls.ll
@@ -168,6 +168,54 @@
   ret i32 %rv
 }
 
+; Duplicate returns to enable tail call optimizations.
+declare i32 @test()
+declare i32 @test1()
+declare i32 @test2()
+declare i32 @test3()
+define i32 @duplicate_returns(i32 %a, i32 %b) nounwind {
+; CHECK-LABEL: duplicate_returns:
+; CHECK:       # %bb.3: # %if.then6
+; CHECK-NEXT:    tail test2
+; CHECK-NEXT:  .LBB13_4: # %if.then
+; CHECK-NEXT:    tail test
+; CHECK-NEXT:  .LBB13_5: # %if.then2
+; CHECK-NEXT:    tail test1
+; CHECK-NEXT:  .LBB13_6: # %if.else8
+; CHECK-NEXT:    tail test3
+entry:
+  %cmp = icmp eq i32 %a, 0
+  br i1 %cmp, label %if.then, label %if.else
+
+if.then:                                          ; preds = %entry
+  %call = tail call i32 @test()
+  br label %return
+
+if.else:                                          ; preds = %entry
+  %cmp1 = icmp eq i32 %b, 0
+  br i1 %cmp1, label %if.then2, label %if.else4
+
+if.then2:                                         ; preds = %if.else
+  %call3 = tail call i32 @test1()
+  br label %return
+
+if.else4:                                         ; preds = %if.else
+  %cmp5 = icmp sgt i32 %a, %b
+  br i1 %cmp5, label %if.then6, label %if.else8
+
+if.then6:                                         ; preds = %if.else4
+  %call7 = tail call i32 @test2()
+  br label %return
+
+if.else8:                                         ; preds = %if.else4
+  %call9 = tail call i32 @test3()
+  br label %return
+
+return:                                           ; preds = %if.else8, %if.then6, %if.then2, %if.then
+  %retval = phi i32 [ %call, %if.then ], [ %call3, %if.then2 ], [ %call7, %if.then6 ], [ %call9, %if.else8 ]
+  ret i32 %retval
+}
+
 !llvm.module.flags = !{!0}
 !0 = !{i32 1, !"ProfileSummary", !1}
 !1 = !{!2, !3, !4, !5, !6, !7, !8, !9}
Index: llvm/lib/Target/RISCV/RISCVISelLowering.h
===================================================================
--- llvm/lib/Target/RISCV/RISCVISelLowering.h
+++ llvm/lib/Target/RISCV/RISCVISelLowering.h
@@ -181,6 +181,7 @@
                                          Type *Ty) const override {
     return true;
   }
+  bool mayBeEmittedAsTailCall(const CallInst *CI) const override;
 
   template <class NodeTy>
   SDValue getAddr(NodeTy *N, SelectionDAG &DAG, bool IsLocal = true) const;
Index: llvm/lib/Target/RISCV/RISCVISelLowering.cpp
===================================================================
--- llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -2494,6 +2494,10 @@
         F, "Argument register required, but has been reserved."});
 }
 
+bool RISCVTargetLowering::mayBeEmittedAsTailCall(const CallInst *CI) const {
+  return CI->isTailCall();
+}
+
 const char *RISCVTargetLowering::getTargetNodeName(unsigned Opcode) const {
   switch ((RISCVISD::NodeType)Opcode) {
   case RISCVISD::FIRST_NUMBER:


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D73699.241423.patch
Type: text/x-patch
Size: 3038 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20200130/8abb7ca5/attachment-0001.bin>