X86: Avoid using _chkstk when lowering WIN_ALLOCA instructions

This patch moves the expansion of WIN_ALLOCA pseudo-instructions
into a separate pass that walks the CFG and lowers the instructions
based on a conservative estimate of the offset between the stack
pointer and the lowest accessed stack address.

The goal is to reduce binary size and run-time costs by removing
calls to _chkstk. While it doesn't fix all the code quality problems
with inalloca calls, it's an incremental improvement for PR27076.

Differential Revision: http://reviews.llvm.org/D20263

llvm-svn: 269828

1 files changed, 6 insertions, 0 deletions

diff --git a/llvm/lib/Target/X86/X86MachineFunctionInfo.h b/llvm/lib/Target/X86/X86MachineFunctionInfo.h
index 4632adaf1e7..d517d82537a 100644
--- a/llvm/lib/Target/X86/X86MachineFunctionInfo.h
+++ b/llvm/lib/Target/X86/X86MachineFunctionInfo.h
@@ -98,6 +98,9 @@ class X86MachineFunctionInfo : public MachineFunctionInfo {
   /// True if this function uses the red zone.
   bool UsesRedZone = false;
 
+  /// True if this function has WIN_ALLOCA instructions.
+  bool HasWinAlloca = false;
+
 private:
   /// ForwardedMustTailRegParms - A list of virtual and physical registers
   /// that must be forwarded to every musttail call.
@@ -172,6 +175,9 @@ public:
 
   bool getUsesRedZone() const { return UsesRedZone; }
   void setUsesRedZone(bool V) { UsesRedZone = V; }
+
+  bool hasWinAlloca() const { return HasWinAlloca; }
+  void setHasWinAlloca(bool v) { HasWinAlloca = v; }
 };
 
 } // End llvm namespace