[SOL] Use ADD for subtracting stack pointer (anza-xyz#70)

This PR replaces sub r11, imm by add r11, -imm and is the equivalent of solana-labs/rbpf#488 for the SBF target in LLVM.

This is the first task in solana-labs/solana#34250

Author: LucasSte

llvm/lib/Target/SBF/SBFFrameLowering.cpp

@@ -16,24 +16,22 @@
 #include "llvm/CodeGen/MachineFrameInfo.h"
 #include "llvm/CodeGen/MachineFunction.h"
 #include "llvm/CodeGen/MachineInstrBuilder.h"
-#include "llvm/CodeGen/MachineRegisterInfo.h"
 
 using namespace llvm;
 
 namespace {
 
 void adjustStackPointer(MachineFunction &MF, MachineBasicBlock &MBB,
-                        MachineBasicBlock::iterator &MBBI,
-                        unsigned int Opcode) {
+                        MachineBasicBlock::iterator &MBBI, bool IsSubtract) {
   MachineFrameInfo &MFI = MF.getFrameInfo();
   int NumBytes = (int)MFI.getStackSize();
   if (NumBytes) {
     DebugLoc Dl;
     const SBFInstrInfo &TII =
         *static_cast<const SBFInstrInfo *>(MF.getSubtarget().getInstrInfo());
-    BuildMI(MBB, MBBI, Dl, TII.get(Opcode), SBF::R11)
+    BuildMI(MBB, MBBI, Dl, TII.get(SBF::ADD_ri), SBF::R11)
         .addReg(SBF::R11)
-        .addImm(NumBytes);
+        .addImm(IsSubtract ? -NumBytes : NumBytes);
   }
 }
 
@@ -47,7 +45,7 @@ void SBFFrameLowering::emitPrologue(MachineFunction &MF,
     return;
   }
   MachineBasicBlock::iterator MBBI = MBB.begin();
-  adjustStackPointer(MF, MBB, MBBI, SBF::SUB_ri);
+  adjustStackPointer(MF, MBB, MBBI, true);
 }
 
 void SBFFrameLowering::emitEpilogue(MachineFunction &MF,
@@ -56,7 +54,7 @@ void SBFFrameLowering::emitEpilogue(MachineFunction &MF,
     return;
   }
   MachineBasicBlock::iterator MBBI = MBB.getLastNonDebugInstr();
-  adjustStackPointer(MF, MBB, MBBI, SBF::ADD_ri);
+  adjustStackPointer(MF, MBB, MBBI, false);
 }
 
 void SBFFrameLowering::determineCalleeSaves(MachineFunction &MF,

llvm/test/CodeGen/SBF/dynamic_stack_frame_add_not_sub.ll

@@ -0,0 +1,31 @@
+; RUN: llc < %s -march=sbf --mattr=+dynamic-frames | FileCheck %s
+;
+; Source:
+; int test_func(int * vec, int idx) {
+;      vec[idx] = idx-1;
+;      return idx;
+;  }
+; Compilation flag:
+; clang -S -emit-llvm test.c
+
+
+; Function Attrs: noinline nounwind optnone ssp uwtable(sync)
+define i32 @test_func(ptr noundef %vec, i32 noundef %idx) #0 {
+; CHECK-LABEL: test_func:
+; CHECK: add64 r11, -16
+; CHECK: add64 r11, 16
+entry:
+  %vec.addr = alloca ptr, align 8
+  %idx.addr = alloca i32, align 4
+  store ptr %vec, ptr %vec.addr, align 8
+  store i32 %idx, ptr %idx.addr, align 4
+  %0 = load i32, ptr %idx.addr, align 4
+  %sub = sub nsw i32 %0, 1
+  %1 = load ptr, ptr %vec.addr, align 8
+  %2 = load i32, ptr %idx.addr, align 4
+  %idxprom = sext i32 %2 to i64
+  %arrayidx = getelementptr inbounds i32, ptr %1, i64 %idxprom
+  store i32 %sub, ptr %arrayidx, align 4
+  %3 = load i32, ptr %idx.addr, align 4
+  ret i32 %3
+}