[PowerPC] Implement mayBeEmittedAsTailCall for PPC

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

Differential Revision: https://reviews.llvm.org/D39777

llvm-svn: 318321

1 files changed, 63 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/PowerPC/duplicate-returns-for-tailcall.ll b/llvm/test/CodeGen/PowerPC/duplicate-returns-for-tailcall.ll
new file mode 100644
index 00000000000..520efd8106f
--- /dev/null
+++ b/llvm/test/CodeGen/PowerPC/duplicate-returns-for-tailcall.ll
@@ -0,0 +1,63 @@
+; RUN: llc -verify-machineinstrs -mcpu=pwr8 -stop-after codegenprepare -mtriple=powerpc64le-unknown-gnu-linux  < %s | FileCheck %s
+; RUN: llc -verify-machineinstrs -mcpu=pwr8 -stop-after codegenprepare -mtriple=powerpc64-unknown-gnu-linux  < %s | FileCheck %s
+
+; Function Attrs: noinline norecurse nounwind readnone
+define hidden signext i32 @call1(i32 signext %a, i32 signext %b, i32 signext %c) local_unnamed_addr #0 {
+entry:
+  %add = add nsw i32 %b, %a
+  %add1 = add nsw i32 %add, %c
+  ret i32 %add1
+}
+
+; Function Attrs: nounwind
+define signext i32 @test(i32 signext %a, i32 signext %b, i32 signext %c) local_unnamed_addr #1 {
+entry:
+  %cmp = icmp eq i32 %a, %b
+  br i1 %cmp, label %if.then, label %if.end
+
+if.then:                                          ; preds = %entry
+  %call = tail call signext i32 @call1(i32 signext %a, i32 signext %b, i32 signext %c)
+  br label %return
+; The return should get duplciated here to enable a tail-call opportunity.
+; CHECK-LABEL: if.then:
+; CHECK-NEXT:  %[[T1:[a-zA-Z0-9]+]] = tail call signext i32 @call1
+; CHECK-NEXT:  ret i32 %[[T1]]
+
+if.end:                                           ; preds = %entry
+  %cmp1 = icmp slt i32 %a, %b
+  br i1 %cmp1, label %if.then2, label %if.end4
+
+if.then2:                                         ; preds = %if.end
+  %call3 = tail call signext i32 @call2(i32 signext %a, i32 signext %b, i32 signext %c) #3
+  br label %return
+; No duplication here since we cannot tail-call an external function anyway.
+; CHECK-LABEL: if.then2:
+; CHECK-NEXT:  tail call signext i32 @call2
+; CHECK-NEXT:  br
+
+if.end4:                                          ; preds = %if.end
+  %cmp5 = icmp sgt i32 %b, %c
+  br i1 %cmp5, label %if.then6, label %return
+
+if.then6:                                         ; preds = %if.end4
+  %call7 = tail call fastcc signext i32 @call3(i32 signext %a, i32 signext %b, i32 signext %c)
+  br label %return
+; No duplication here because the calling convention mismatch means we won't tail-call
+; CHECK_LABEL: if.then13:
+; CHECK:       tail call fastcc signext i32 @call3
+; CHECK-NEXT:  br
+
+return:                                           ; preds = %if.end4, %if.then6, %if.then2, %if.then
+  %retval.0 = phi i32 [ %call, %if.then ], [ %call3, %if.then2 ], [ %call7, %if.then6 ], [ %c, %if.end4 ]
+  ret i32 %retval.0
+}
+
+declare signext i32 @call2(i32 signext, i32 signext, i32 signext) local_unnamed_addr #2
+
+; Function Attrs: noinline norecurse nounwind readnone
+define internal fastcc signext i32 @call3(i32 signext %a, i32 signext %b, i32 signext %c) unnamed_addr #0 {
+entry:
+  %mul = mul nsw i32 %b, %a
+  %mul1 = mul nsw i32 %mul, %c
+  ret i32 %mul1
+}