[WebAssembly] Emit a BasePointer when we have overly-aligned stack objects

Because we shift the stack pointer by an unknown amount, we need an
additional pointer. In the case where we have variable-size objects
as well, we can't reuse the frame pointer, thus three pointers.

Patch by Jacob Gravelle

Differential Revision: https://reviews.llvm.org/D26263

llvm-svn: 286160

1 files changed, 10 insertions, 0 deletions

diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyMachineFunctionInfo.h b/llvm/lib/Target/WebAssembly/WebAssemblyMachineFunctionInfo.h
index c5702ce11ad..756619bebbe 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyMachineFunctionInfo.h
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyMachineFunctionInfo.h
@@ -46,6 +46,10 @@ class WebAssemblyFunctionInfo final : public MachineFunctionInfo {
   // TLI::LowerVASTART
   unsigned VarargVreg = -1U;
 
+  // A virtual register holding the base pointer for functions that have
+  // overaligned values on the user stack.
+  unsigned BasePtrVreg = -1U;
+
  public:
   explicit WebAssemblyFunctionInfo(MachineFunction &MF) : MF(MF) {}
   ~WebAssemblyFunctionInfo() override;
@@ -65,6 +69,12 @@ class WebAssemblyFunctionInfo final : public MachineFunctionInfo {
   }
   void setVarargBufferVreg(unsigned Reg) { VarargVreg = Reg; }
 
+  unsigned getBasePointerVreg() const {
+    assert(BasePtrVreg != -1U && "Base ptr vreg hasn't been set");
+    return BasePtrVreg;
+  }
+  void setBasePointerVreg(unsigned Reg) { BasePtrVreg = Reg; }
+
   static const unsigned UnusedReg = -1u;
 
   void stackifyVReg(unsigned VReg) {