[RISCV] Fixing stack offset for RVV object with vararg in stack.

We found LLVM generate wrong stack offset for RVV object when stack
having variable argument, that cause by we didn't count vaarg part during
calculate RVV stack objects.

Also update the stack layout diagram for including vaarg in the diagram.

Stack layout ref:
https://github.com/gcc-mirror/gcc/blob/master/gcc/config/riscv/riscv.cc#L3941

Reviewed By: rogfer01

Differential Revision: https://reviews.llvm.org/D123180

Author: kito-cheng

llvm/lib/Target/RISCV/RISCVFrameLowering.cpp

@@ -674,7 +674,10 @@ RISCVFrameLowering::getFrameIndexReference(const MachineFunction &MF, int FI,
     if (hasBP(MF)) {
       FrameReg = RISCVABI::getBPReg();
       // |--------------------------| -- <-- FP
-      // | callee-saved registers   | | <----.
+      // | callee-allocated save    | | <----|
+      // | area for register varargs| |      |
+      // |--------------------------| |      |
+      // | callee-saved registers   | |      |
       // |--------------------------| --     |
       // | realignment (the size of | |      |
       // | this area is not counted | |      |
@@ -699,7 +702,10 @@ RISCVFrameLowering::getFrameIndexReference(const MachineFunction &MF, int FI,
     } else {
       FrameReg = RISCV::X2;
       // |--------------------------| -- <-- FP
-      // | callee-saved registers   | | <----.
+      // | callee-allocated save    | | <----|
+      // | area for register varargs| |      |
+      // |--------------------------| |      |
+      // | callee-saved registers   | |      |
       // |--------------------------| --     |
       // | realignment (the size of | |      |
       // | this area is not counted | |      |
@@ -742,6 +748,9 @@ RISCVFrameLowering::getFrameIndexReference(const MachineFunction &MF, int FI,
       // the frame size.
       //
       // |--------------------------| -- <-- FP
+      // | callee-allocated save    | |
+      // | area for register varargs| |
+      // |--------------------------| |
       // | callee-saved registers   | |
       // |--------------------------| | MFI.getStackSize()
       // | scalar local variables   | |
@@ -756,7 +765,10 @@ RISCVFrameLowering::getFrameIndexReference(const MachineFunction &MF, int FI,
       // When using SP to access frame objects, we need to add RVV stack size.
       //
       // |--------------------------| -- <-- FP
-      // | callee-saved registers   | | <----.
+      // | callee-allocated save    | | <----|
+      // | area for register varargs| |      |
+      // |--------------------------| |      |
+      // | callee-saved registers   | |      |
       // |--------------------------| --     |
       // | Padding after RVV        | |      |
       // | (not counted in          | |      |
@@ -786,8 +798,11 @@ RISCVFrameLowering::getFrameIndexReference(const MachineFunction &MF, int FI,
           Offset += StackOffset::getFixed(MFI.getStackSize());
         }
       } else if (MFI.getStackID(FI) == TargetStackID::ScalableVector) {
+        int ScalarLocalVarSize = MFI.getStackSize() -
+                                 RVFI->getCalleeSavedStackSize() -
+                                 RVFI->getVarArgsSaveSize();
         Offset += StackOffset::get(
-            alignTo(MFI.getStackSize() - RVFI->getCalleeSavedStackSize(), 8),
+            alignTo(ScalarLocalVarSize, 8),
             RVFI->getRVVStackSize());
       }
     }

llvm/test/CodeGen/RISCV/rvv/wrong-stack-offset-for-rvv-object.mir

@@ -164,7 +164,7 @@ body:             |
   ; CHECK-NEXT:   SD killed renamable $x16, killed $x10, 48 :: (store (s64) into %fixed-stack.1, align 16)
   ; CHECK-NEXT:   dead $x0 = PseudoVSETIVLI 2, 69, implicit-def $vl, implicit-def $vtype
   ; CHECK-NEXT:   renamable $v8 = PseudoVMV_V_I_MF8 0, 2, 3, implicit $vl, implicit $vtype
-  ; CHECK-NEXT:   $x10 = ADDI $x2, 40
+  ; CHECK-NEXT:   $x10 = ADDI $x2, 24
   ; CHECK-NEXT:   PseudoVSPILL_M1 killed renamable $v8, killed $x10 :: (store unknown-size into %stack.1, align 8)
   ; CHECK-NEXT: {{  $}}
   ; CHECK-NEXT: bb.1.while.cond:
@@ -179,7 +179,7 @@ body:             |
   ; CHECK-NEXT:   liveins: $x8, $x9
   ; CHECK-NEXT: {{  $}}
   ; CHECK-NEXT:   dead $x0 = PseudoVSETIVLI 2, 69, implicit-def $vl, implicit-def $vtype
-  ; CHECK-NEXT:   $x10 = ADDI $x2, 40
+  ; CHECK-NEXT:   $x10 = ADDI $x2, 24
   ; CHECK-NEXT:   renamable $v8 = PseudoVRELOAD_M1 killed $x10 :: (load unknown-size from %stack.1, align 8)
   ; CHECK-NEXT:   PseudoVSE8_V_MF8 killed renamable $v8, renamable $x8, 2, 3, implicit $vl, implicit $vtype :: (store (s16) into %ir.0, align 1)
   ; CHECK-NEXT:   $x10 = COPY renamable $x9