Implement Red Zone utilization on x86-64. This is currently

disabled by default; I'll enable it when I hook it up with
the llvm-gcc flag which controls it.

llvm-svn: 63056

1 files changed, 12 insertions, 0 deletions

diff --git a/llvm/lib/Target/X86/X86RegisterInfo.cpp b/llvm/lib/Target/X86/X86RegisterInfo.cpp
index a0d8b58b789..08746f2ffb4 100644
--- a/llvm/lib/Target/X86/X86RegisterInfo.cpp
+++ b/llvm/lib/Target/X86/X86RegisterInfo.cpp
@@ -721,6 +721,18 @@ void X86RegisterInfo::emitPrologue(MachineFunction &MF) const {
   // Get desired stack alignment
   uint64_t MaxAlign  = MFI->getMaxAlignment();
 
+  // If this is x86-64 and the Red Zone is not disabled, if we are a leaf
+  // function, and use up to 128 bytes of stack space, don't have a frame
+  // pointer, calls, or dynamic alloca then we do not need to adjust the
+  // stack pointer (we fit in the Red Zone).
+  if (Is64Bit && !DisableRedZone &&
+      !MFI->hasVarSizedObjects() &&                // No dynamic alloca.
+      !MFI->hasCalls()) {                          // No calls.
+    StackSize = std::max((uint64_t)X86FI->getCalleeSavedFrameSize(),
+                         StackSize > 128 ? StackSize - 128 : 0);
+    MFI->setStackSize(StackSize);
+  }
+
   // Add RETADDR move area to callee saved frame size.
   int TailCallReturnAddrDelta = X86FI->getTCReturnAddrDelta();
   if (TailCallReturnAddrDelta < 0)