JIT: arm64 osr funclet frame probing

We currently need to pad OSR funclet frames with the full size of the
Tier0 frame, and this paddign sits above the register save area. For
large Tier0 frames we thus need to probe the stack in the OSR prolog
for type1 and type3 frames, before doing the initial SP adjustment and
save.

Longer term the plan is to revise arm64 OSR so we will not need to
do this padding; at that point we can remove this extra probing.

Fixes dotnet#70263.

src/coreclr/jit/codegenarm64.cpp

@@ -1377,10 +1377,12 @@ void CodeGen::genFuncletProlog(BasicBlock* block)
 
     if (genFuncletInfo.fiFrameType == 1)
     {
-        // With OSR we may see large values for fiSpDelta1
-        // (we really need to probe the frame, sigh)
         if (compiler->opts.IsOSR())
         {
+            // With OSR we may see large values for fiSpDelta1.
+            // We repurpose genAllocLclFram to do the necessary probing.
+            bool scratchRegIsZero = false;
+            genAllocLclFrame(-genFuncletInfo.fiSpDelta1, REG_SCRATCH, &scratchRegIsZero, maskArgRegsLiveIn);
             genStackPointerAdjustment(genFuncletInfo.fiSpDelta1, REG_SCRATCH, nullptr, /* reportUnwindData */ true);
             GetEmitter()->emitIns_R_R_R_I(INS_stp, EA_PTRSIZE, REG_FP, REG_LR, REG_SPBASE, 0);
             compiler->unwindSaveRegPair(REG_FP, REG_LR, 0);
@@ -1416,10 +1418,12 @@ void CodeGen::genFuncletProlog(BasicBlock* block)
     }
     else if (genFuncletInfo.fiFrameType == 3)
     {
-        // With OSR we may see large values for fiSpDelta1
-        // (we really need to probe the frame, sigh)
         if (compiler->opts.IsOSR())
         {
+            // With OSR we may see large values for fiSpDelta1
+            // We repurpose genAllocLclFram to do the necessary probing.
+            bool scratchRegIsZero = false;
+            genAllocLclFrame(-genFuncletInfo.fiSpDelta1, REG_SCRATCH, &scratchRegIsZero, maskArgRegsLiveIn);
             genStackPointerAdjustment(genFuncletInfo.fiSpDelta1, REG_SCRATCH, nullptr, /* reportUnwindData */ true);
             GetEmitter()->emitIns_R_R_R_I(INS_stp, EA_PTRSIZE, REG_FP, REG_LR, REG_SPBASE, 0);
             compiler->unwindSaveRegPair(REG_FP, REG_LR, 0);