Do not insert a tail call when returning multiple values on X86

[loladiro]

Summary

This fixes http://llvm.org/bugs/show_bug.cgi?id=19530. The problem is that X86ISelLowering erroneously thought the third call was eligible for tail call elimination. It would have been if it's return value was actually the one returned by the calling function, but here that is not the case and additional values are being returned.

[• rafael]

+; RUN: llc < %s -mcpu=core2 | FileCheck %s

You might want to use -mtriple just to be sure.

+; See PR19530
+declare double @llvm.powi.f64(double %Val, i32 %power)
+define <3 x double> @julia_foo17589(i64) {
+top:
+ %1 = trunc i64 %0 to i32
+ %2 = call double @llvm.powi.f64(double 1.000000e+00, i32 %1)
+; CHECK: callq powidf2
+ %3 = insertelement <3 x double> undef, double %2, i32 0
+ %4 = call double @llvm.powi.f64(double 2.000000e+00, i32 %1)
+; CHECK: callq powidf2
+ %5 = insertelement <3 x double> %3, double %4, i32 1
+ %6 = call double @llvm.powi.f64(double 3.000000e+00, i32 %1)
+; CHECK: callq __powidf2
+ %7 = insertelement <3 x double> %5, double %6, i32 2
+; CHECK-NOT: TAILCALL
+ ret <3 x double> %7
+}

The test can be a bit simple without the trunc and and easier to read
by using named instructions:

declare double @llvm.powi.f64(double, i32)

define <3 x double> @julia_foo17589(i32 %arg) {

%tmp1 = call double @llvm.powi.f64(double 1.000000e+00, i32 %arg)
%tmp2 = insertelement <3 x double> undef, double %tmp1, i32 0
%tmp3 = call double @llvm.powi.f64(double 2.000000e+00, i32 %arg)
%tmp4 = insertelement <3 x double> %tmp2, double %tmp3, i32 1
%tmp5 = call double @llvm.powi.f64(double 3.000000e+00, i32 %arg)
%tmp6 = insertelement <3 x double> %tmp4, double %tmp5, i32 2
ret <3 x double> %tmp6

}

\ No newline at end of file

please add one :-)

[loladiro]

Updated the test case based on comments.

[• rafael]

LGTM

[loladiro]

Closed by commit rL216117 (authored by kfischer).

lib/Target/X86/X86ISelLowering.cpp

bool X86TargetLowering::isUsedByReturnOnly(SDNode *N, SDValue &Chain) const {
   } else if (Copy->getOpcode() != ISD::FP_EXTEND)
     return false;
 
   bool HasRet = false;
   for (SDNode::use_iterator UI = Copy->use_begin(), UE = Copy->use_end();
        UI != UE; ++UI) {
     if (UI->getOpcode() != X86ISD::RET_FLAG)
       return false;
+    // If we are returning more than one value, we can definitely
+    // not make a tail call see PR19530
+    if (UI->getNumOperands() > 4)
+      return false;
+    if (UI->getNumOperands() == 4 &&
+        UI->getOperand(UI->getNumOperands()-1).getValueType() != MVT::Glue)
+      return false;
     HasRet = true;
   }
 
   if (!HasRet)
     return false;
 
   Chain = TCChain;
   return true;

test/CodeGen/X86/tailcall-multiret.ll

+; RUN: llc < %s -mtriple=x86_64-linux-gnu -mcpu=core2 | FileCheck %s
+; See PR19530
+declare double    @llvm.powi.f64(double %Val, i32 %power)
+define <3 x double> @julia_foo17589(i32 %arg) {
+  %tmp1 = call double @llvm.powi.f64(double 1.000000e+00, i32 %arg)
+; CHECK: callq   __powidf2
+  %tmp2 = insertelement <3 x double> undef, double %tmp1, i32 0
+  %tmp3 = call double @llvm.powi.f64(double 2.000000e+00, i32 %arg)
+; CHECK: callq   __powidf2
+  %tmp4 = insertelement <3 x double> %tmp2, double %tmp3, i32 1
+  %tmp5 = call double @llvm.powi.f64(double 3.000000e+00, i32 %arg)
+; CHECK: callq   __powidf2
+  %tmp6 = insertelement <3 x double> %tmp4, double %tmp5, i32 2
+; CHECK-NOT: TAILCALL
+  ret <3 x double> %tmp6
+}
+