[llvm] [RISCV] Allocate the varargs GPR save area as a single object. (PR #74354)

[Wang Pengcheng via llvm-commits]

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@@ -17691,49 +17691,49 @@ SDValue RISCVTargetLowering::LowerFormalArguments(
     MachineRegisterInfo &RegInfo = MF.getRegInfo();
     RISCVMachineFunctionInfo *RVFI = MF.getInfo<RISCVMachineFunctionInfo>();
 
-    // Offset of the first variable argument from stack pointer, and size of
-    // the vararg save area. For now, the varargs save area is either zero or
-    // large enough to hold a0-a7.
-    int VaArgOffset;
+    // Size of the vararg save area. For now, the varargs save area is either
+    // zero or large enough to hold a0-a7.
     int VarArgsSaveSize = XLenInBytes * (ArgRegs.size() - Idx);
+    int FI;
 
     // If all registers are allocated, then all varargs must be passed on the
     // stack and we don't need to save any argregs.
     if (VarArgsSaveSize == 0) {
-      VaArgOffset = CCInfo.getStackSize();
+      int VaArgOffset = CCInfo.getStackSize();
+      FI = MFI.CreateFixedObject(XLenInBytes, VaArgOffset, true);
     } else {
-      VaArgOffset = -VarArgsSaveSize;
+      int VaArgOffset = -VarArgsSaveSize;
+      FI = MFI.CreateFixedObject(VarArgsSaveSize, VaArgOffset, true);
+
+      // If saving an odd number of registers then create an extra stack slot to
+      // ensure that the frame pointer is 2*XLEN-aligned, which in turn ensures
+      // offsets to even-numbered registered remain 2*XLEN-aligned.
+      if (Idx % 2) {
+        MFI.CreateFixedObject(XLenInBytes, VaArgOffset - (int)XLenInBytes,
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wangpc-pp wrote:

Ditto.

https://github.com/llvm/llvm-project/pull/74354