commit f9b67b810e2d413606b0d5891ed9477d819bcab9
author Reid Kleckner <rnk@google.com> Mon Oct 07 22:28:58 2019 +0000
committer Reid Kleckner <rnk@google.com> Mon Oct 07 22:28:58 2019 +0000
tree f5bc8a674f930c49b92f653ea7e46be53f13c084
parent daeead4b02f062bf5a21e154ab7726b3e1dd41bd

[X86] Add new calling convention that guarantees tail call optimization

When the target option GuaranteedTailCallOpt is specified, calls with
the fastcc calling convention will be transformed into tail calls if
they are in tail position. This diff adds a new calling convention,
tailcc, currently supported only on X86, which behaves the same way as
fastcc, except that the GuaranteedTailCallOpt flag does not need to
enabled in order to enable tail call optimization.

Patch by Dwight Guth <dwight.guth@runtimeverification.com>!

Reviewed By: lebedev.ri, paquette, rnk

Differential Revision: https://reviews.llvm.org/D67855

llvm-svn: 373976

llvm/lib/Target/X86/X86FastISel.cpp

diff --git a/llvm/lib/Target/X86/X86FastISel.cpp b/llvm/lib/Target/X86/X86FastISel.cpp
index 97abd08..e5e089d 100644
--- a/llvm/lib/Target/X86/X86FastISel.cpp
+++ b/llvm/lib/Target/X86/X86FastISel.cpp
@@ -1160,6 +1160,7 @@
   CallingConv::ID CC = F.getCallingConv();
   if (CC != CallingConv::C &&
       CC != CallingConv::Fast &&
+      CC != CallingConv::Tail &&
       CC != CallingConv::X86_FastCall &&
       CC != CallingConv::X86_StdCall &&
       CC != CallingConv::X86_ThisCall &&
@@ -1173,7 +1174,8 @@
 
   // fastcc with -tailcallopt is intended to provide a guaranteed
   // tail call optimization. Fastisel doesn't know how to do that.
-  if (CC == CallingConv::Fast && TM.Options.GuaranteedTailCallOpt)
+  if ((CC == CallingConv::Fast && TM.Options.GuaranteedTailCallOpt) ||
+      CC == CallingConv::Tail)
     return false;
 
   // Let SDISel handle vararg functions.
@@ -3157,7 +3159,7 @@
   if (Subtarget->getTargetTriple().isOSMSVCRT())
     return 0;
   if (CC == CallingConv::Fast || CC == CallingConv::GHC ||
-      CC == CallingConv::HiPE)
+      CC == CallingConv::HiPE || CC == CallingConv::Tail)
     return 0;
 
   if (CS)
@@ -3208,6 +3210,7 @@
   default: return false;
   case CallingConv::C:
   case CallingConv::Fast:
+  case CallingConv::Tail:
   case CallingConv::WebKit_JS:
   case CallingConv::Swift:
   case CallingConv::X86_FastCall:
@@ -3224,7 +3227,8 @@
 
   // fastcc with -tailcallopt is intended to provide a guaranteed
   // tail call optimization. Fastisel doesn't know how to do that.
-  if (CC == CallingConv::Fast && TM.Options.GuaranteedTailCallOpt)
+  if ((CC == CallingConv::Fast && TM.Options.GuaranteedTailCallOpt) ||
+      CC == CallingConv::Tail)
     return false;
 
   // Don't know how to handle Win64 varargs yet.  Nothing special needed for