[LoongArch] Implement mayBeEmittedAsTailCall for tail call optimization

Implements TargetLowering callback `mayBeEmittedAsTailCall` that enables
CodeGenPrepare to duplicate returns when they might enable a tail-call.

Reviewed By: xen0n, MaskRay

Differential Revision: https://reviews.llvm.org/D141257

diff --git a/llvm/lib/Target/LoongArch/LoongArchISelLowering.cpp b/llvm/lib/Target/LoongArch/LoongArchISelLowering.cpp
index 61fda67..4a64a94 100644 (file)
--- a/llvm/lib/Target/LoongArch/LoongArchISelLowering.cpp
+++ b/llvm/lib/Target/LoongArch/LoongArchISelLowering.cpp
@@ -2326,6 +2326,10 @@ SDValue LoongArchTargetLowering::LowerFormalArguments(
   return Chain;
 }
 
+bool LoongArchTargetLowering::mayBeEmittedAsTailCall(const CallInst *CI) const {
+  return CI->isTailCall();
+}
+
 // Check whether the call is eligible for tail call optimization.
 bool LoongArchTargetLowering::isEligibleForTailCallOptimization(
     CCState &CCInfo, CallLoweringInfo &CLI, MachineFunction &MF,

diff --git a/llvm/lib/Target/LoongArch/LoongArchISelLowering.h b/llvm/lib/Target/LoongArch/LoongArchISelLowering.h
index 976aae3..0ddcda6 100644 (file)
--- a/llvm/lib/Target/LoongArch/LoongArchISelLowering.h
+++ b/llvm/lib/Target/LoongArch/LoongArchISelLowering.h
@@ -176,6 +176,7 @@ public:
 
   Register getRegisterByName(const char *RegName, LLT VT,
                              const MachineFunction &MF) const override;
+  bool mayBeEmittedAsTailCall(const CallInst *CI) const override;
 
   bool decomposeMulByConstant(LLVMContext &Context, EVT VT,
                               SDValue C) const override;

diff --git a/llvm/test/CodeGen/LoongArch/bnez-beqz.ll b/llvm/test/CodeGen/LoongArch/bnez-beqz.ll
index b4b2c3e..d1652c7 100644 (file)
--- a/llvm/test/CodeGen/LoongArch/bnez-beqz.ll
+++ b/llvm/test/CodeGen/LoongArch/bnez-beqz.ll
@@ -7,27 +7,19 @@ declare void @bar()
 define void @bnez_i32(i32 signext %0) nounwind {
 ; LA32-LABEL: bnez_i32:
 ; LA32:       # %bb.0: # %start
-; LA32-NEXT:    addi.w $sp, $sp, -16
-; LA32-NEXT:    st.w $ra, $sp, 12 # 4-byte Folded Spill
-; LA32-NEXT:    bnez $a0, .LBB0_2
-; LA32-NEXT:  # %bb.1: # %t
-; LA32-NEXT:    bl %plt(bar)
-; LA32-NEXT:  .LBB0_2: # %f
-; LA32-NEXT:    ld.w $ra, $sp, 12 # 4-byte Folded Reload
-; LA32-NEXT:    addi.w $sp, $sp, 16
+; LA32-NEXT:    beqz $a0, .LBB0_2
+; LA32-NEXT:  # %bb.1: # %f
 ; LA32-NEXT:    ret
+; LA32-NEXT:  .LBB0_2: # %t
+; LA32-NEXT:    b %plt(bar)
 ;
 ; LA64-LABEL: bnez_i32:
 ; LA64:       # %bb.0: # %start
-; LA64-NEXT:    addi.d $sp, $sp, -16
-; LA64-NEXT:    st.d $ra, $sp, 8 # 8-byte Folded Spill
-; LA64-NEXT:    bnez $a0, .LBB0_2
-; LA64-NEXT:  # %bb.1: # %t
-; LA64-NEXT:    bl %plt(bar)
-; LA64-NEXT:  .LBB0_2: # %f
-; LA64-NEXT:    ld.d $ra, $sp, 8 # 8-byte Folded Reload
-; LA64-NEXT:    addi.d $sp, $sp, 16
+; LA64-NEXT:    beqz $a0, .LBB0_2
+; LA64-NEXT:  # %bb.1: # %f
 ; LA64-NEXT:    ret
+; LA64-NEXT:  .LBB0_2: # %t
+; LA64-NEXT:    b %plt(bar)
 start:
   %1 = icmp eq i32 %0, 0
   br i1 %1, label %t, label %f
@@ -43,26 +35,18 @@ f:
 define void @beqz_i32(i32 signext %0) nounwind {
 ; LA32-LABEL: beqz_i32:
 ; LA32:       # %bb.0: # %start
-; LA32-NEXT:    addi.w $sp, $sp, -16
-; LA32-NEXT:    st.w $ra, $sp, 12 # 4-byte Folded Spill
 ; LA32-NEXT:    beqz $a0, .LBB1_2
 ; LA32-NEXT:  # %bb.1: # %t
-; LA32-NEXT:    bl %plt(bar)
+; LA32-NEXT:    b %plt(bar)
 ; LA32-NEXT:  .LBB1_2: # %f
-; LA32-NEXT:    ld.w $ra, $sp, 12 # 4-byte Folded Reload
-; LA32-NEXT:    addi.w $sp, $sp, 16
 ; LA32-NEXT:    ret
 ;
 ; LA64-LABEL: beqz_i32:
 ; LA64:       # %bb.0: # %start
-; LA64-NEXT:    addi.d $sp, $sp, -16
-; LA64-NEXT:    st.d $ra, $sp, 8 # 8-byte Folded Spill
 ; LA64-NEXT:    beqz $a0, .LBB1_2
 ; LA64-NEXT:  # %bb.1: # %t
-; LA64-NEXT:    bl %plt(bar)
+; LA64-NEXT:    b %plt(bar)
 ; LA64-NEXT:  .LBB1_2: # %f
-; LA64-NEXT:    ld.d $ra, $sp, 8 # 8-byte Folded Reload
-; LA64-NEXT:    addi.d $sp, $sp, 16
 ; LA64-NEXT:    ret
 start:
   %1 = icmp ne i32 %0, 0
@@ -79,28 +63,20 @@ f:
 define void @bnez_i64(i64 %0) nounwind {
 ; LA32-LABEL: bnez_i64:
 ; LA32:       # %bb.0: # %start
-; LA32-NEXT:    addi.w $sp, $sp, -16
-; LA32-NEXT:    st.w $ra, $sp, 12 # 4-byte Folded Spill
 ; LA32-NEXT:    or $a0, $a0, $a1
-; LA32-NEXT:    bnez $a0, .LBB2_2
-; LA32-NEXT:  # %bb.1: # %t
-; LA32-NEXT:    bl %plt(bar)
-; LA32-NEXT:  .LBB2_2: # %f
-; LA32-NEXT:    ld.w $ra, $sp, 12 # 4-byte Folded Reload
-; LA32-NEXT:    addi.w $sp, $sp, 16
+; LA32-NEXT:    beqz $a0, .LBB2_2
+; LA32-NEXT:  # %bb.1: # %f
 ; LA32-NEXT:    ret
+; LA32-NEXT:  .LBB2_2: # %t
+; LA32-NEXT:    b %plt(bar)
 ;
 ; LA64-LABEL: bnez_i64:
 ; LA64:       # %bb.0: # %start
-; LA64-NEXT:    addi.d $sp, $sp, -16
-; LA64-NEXT:    st.d $ra, $sp, 8 # 8-byte Folded Spill
-; LA64-NEXT:    bnez $a0, .LBB2_2
-; LA64-NEXT:  # %bb.1: # %t
-; LA64-NEXT:    bl %plt(bar)
-; LA64-NEXT:  .LBB2_2: # %f
-; LA64-NEXT:    ld.d $ra, $sp, 8 # 8-byte Folded Reload
-; LA64-NEXT:    addi.d $sp, $sp, 16
+; LA64-NEXT:    beqz $a0, .LBB2_2
+; LA64-NEXT:  # %bb.1: # %f
 ; LA64-NEXT:    ret
+; LA64-NEXT:  .LBB2_2: # %t
+; LA64-NEXT:    b %plt(bar)
 start:
   %1 = icmp eq i64 %0, 0
   br i1 %1, label %t, label %f
@@ -116,27 +92,19 @@ f:
 define void @beqz_i64(i64 %0) nounwind {
 ; LA32-LABEL: beqz_i64:
 ; LA32:       # %bb.0: # %start
-; LA32-NEXT:    addi.w $sp, $sp, -16
-; LA32-NEXT:    st.w $ra, $sp, 12 # 4-byte Folded Spill
 ; LA32-NEXT:    or $a0, $a0, $a1
 ; LA32-NEXT:    beqz $a0, .LBB3_2
 ; LA32-NEXT:  # %bb.1: # %t
-; LA32-NEXT:    bl %plt(bar)
+; LA32-NEXT:    b %plt(bar)
 ; LA32-NEXT:  .LBB3_2: # %f
-; LA32-NEXT:    ld.w $ra, $sp, 12 # 4-byte Folded Reload
-; LA32-NEXT:    addi.w $sp, $sp, 16
 ; LA32-NEXT:    ret
 ;
 ; LA64-LABEL: beqz_i64:
 ; LA64:       # %bb.0: # %start
-; LA64-NEXT:    addi.d $sp, $sp, -16
-; LA64-NEXT:    st.d $ra, $sp, 8 # 8-byte Folded Spill
 ; LA64-NEXT:    beqz $a0, .LBB3_2
 ; LA64-NEXT:  # %bb.1: # %t
-; LA64-NEXT:    bl %plt(bar)
+; LA64-NEXT:    b %plt(bar)
 ; LA64-NEXT:  .LBB3_2: # %f
-; LA64-NEXT:    ld.d $ra, $sp, 8 # 8-byte Folded Reload
-; LA64-NEXT:    addi.d $sp, $sp, 16
 ; LA64-NEXT:    ret
 start:
   %1 = icmp ne i64 %0, 0

diff --git a/llvm/test/CodeGen/LoongArch/duplicate-returns-for-tailcall.ll b/llvm/test/CodeGen/LoongArch/duplicate-returns-for-tailcall.ll
new file mode 100644 (file)
index 0000000..59bc9aa
--- /dev/null
+++ b/llvm/test/CodeGen/LoongArch/duplicate-returns-for-tailcall.ll
@@ -0,0 +1,60 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc --mtriple=loongarch64 < %s | FileCheck %s
+
+;; Perform tail call optimization for duplicate returns.
+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.0: # %entry
+; CHECK-NEXT:    bstrpick.d $a2, $a0, 31, 0
+; CHECK-NEXT:    beqz $a2, .LBB0_4
+; CHECK-NEXT:  # %bb.1: # %if.else
+; CHECK-NEXT:    bstrpick.d $a2, $a1, 31, 0
+; CHECK-NEXT:    beqz $a2, .LBB0_5
+; CHECK-NEXT:  # %bb.2: # %if.else2
+; CHECK-NEXT:    addi.w $a0, $a0, 0
+; CHECK-NEXT:    addi.w $a1, $a1, 0
+; CHECK-NEXT:    bge $a1, $a0, .LBB0_6
+; CHECK-NEXT:  # %bb.3: # %if.then3
+; CHECK-NEXT:    b %plt(test2)
+; CHECK-NEXT:  .LBB0_4: # %if.then
+; CHECK-NEXT:    b %plt(test)
+; CHECK-NEXT:  .LBB0_5: # %if.then2
+; CHECK-NEXT:    b %plt(test1)
+; CHECK-NEXT:  .LBB0_6: # %if.else3
+; CHECK-NEXT:    b %plt(test3)
+entry:
+  %cmp = icmp eq i32 %a, 0
+  br i1 %cmp, label %if.then, label %if.else
+
+if.then:
+  %call = tail call i32 @test()
+  br label %return
+
+if.else:
+  %cmp1 = icmp eq i32 %b, 0
+  br i1 %cmp1, label %if.then2, label %if.else2
+
+if.then2:
+  %call1 = tail call i32 @test1()
+  br label %return
+
+if.else2:
+  %cmp5 = icmp sgt i32 %a, %b
+  br i1 %cmp5, label %if.then3, label %if.else3
+
+if.then3:
+  %call2 = tail call i32 @test2()
+  br label %return
+
+if.else3:
+  %call3 = tail call i32 @test3()
+  br label %return
+
+return:
+  %retval = phi i32 [ %call, %if.then ], [ %call1, %if.then2 ], [ %call2, %if.then3 ], [ %call3, %if.else3 ]
+  ret i32 %retval
+}