[MIPS] Implement support for -mstack-alignment.

Summary:
This is modeled on the implementation for x86 which stores the command line
option in a 'StackAlignOverride' field in MipsSubtarget and then uses this
to compute a 'stackAlignment' value in
MipsSubtarget::initializeSubtargetDependencies.

The stackAlignment() method in MipsSubTarget is renamed to getStackAlignment()
and returns the computed 'stackAlignment'.

Reviewers: sdardis

Reviewed By: sdardis

Subscribers: llvm-commits, arichardson

Differential Revision: https://reviews.llvm.org/D35874

llvm-svn: 310891

1 files changed, 9 insertions, 4 deletions

diff --git a/llvm/lib/Target/Mips/MipsSubtarget.h b/llvm/lib/Target/Mips/MipsSubtarget.h
index ef04c931138..0c9688865c1 100644
--- a/llvm/lib/Target/Mips/MipsSubtarget.h
+++ b/llvm/lib/Target/Mips/MipsSubtarget.h
@@ -155,6 +155,13 @@ class MipsSubtarget : public MipsGenSubtargetInfo {
   // Disable use of the `jal` instruction.
   bool UseLongCalls = false;
 
+  /// The minimum alignment known to hold of the stack frame on
+  /// entry to the function and which must be maintained by every function.
+  unsigned stackAlignment;
+
+  /// The overridden stack alignment.
+  unsigned StackAlignOverride;
+
   InstrItineraryData InstrItins;
 
   // We can override the determination of whether we are in mips16 mode
@@ -186,7 +193,7 @@ public:
   /// This constructor initializes the data members to match that
   /// of the specified triple.
   MipsSubtarget(const Triple &TT, StringRef CPU, StringRef FS, bool little,
-                const MipsTargetMachine &TM);
+                const MipsTargetMachine &TM, unsigned StackAlignOverride);
 
   /// ParseSubtargetFeatures - Parses features string setting specified
   /// subtarget options.  Definition of function is auto generated by tblgen.
@@ -295,9 +302,7 @@ public:
   // really use them if in addition we are in mips16 mode
   static bool useConstantIslands();
 
-  unsigned stackAlignment() const {
-    return isABI_N32() || isABI_N64() ? 16 : 8;
-  }
+  unsigned getStackAlignment() const { return stackAlignment; }
 
   // Grab relocation model
   Reloc::Model getRelocationModel() const;