[llvm] [RISCV] fix SP recovery in a function epilogue (PR #110809)

[Kito Cheng via llvm-commits]

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@@ -786,74 +799,90 @@ void RISCVFrameLowering::emitEpilogue(MachineFunction &MF,
       --MBBI;
   }
 
-  const auto &CSI = getUnmanagedCSI(MF, MFI.getCalleeSavedInfo());
+  const auto &CSI = MFI.getCalleeSavedInfo();
 
   // Skip to before the restores of scalar callee-saved registers
   // FIXME: assumes exactly one instruction is used to restore each
   // callee-saved register.
-  auto LastFrameDestroy = MBBI;
-  if (!CSI.empty())
-    LastFrameDestroy = std::prev(MBBI, CSI.size());
+  auto LastFrameDestroy = std::prev(MBBI, getUnmanagedCSI(MF, CSI).size());
 
-  uint64_t RealStackSize = getStackSizeWithRVVPadding(MF);
-  uint64_t StackSize = RealStackSize - RVFI->getReservedSpillsSize();
-  uint64_t FPOffset = RealStackSize - RVFI->getVarArgsSaveSize();
+  uint64_t FirstSPAdjustAmount = getFirstSPAdjustAmount(MF);
+  uint64_t RealStackSize = FirstSPAdjustAmount ? FirstSPAdjustAmount
+                                               : getStackSizeWithRVVPadding(MF);
+  uint64_t StackSize = FirstSPAdjustAmount ? FirstSPAdjustAmount
+                                           : getStackSizeWithRVVPadding(MF) -
+                                                 RVFI->getReservedSpillsSize();
+  uint64_t FPOffset = FirstSPAdjustAmount ? FirstSPAdjustAmount
+                                          : getStackSizeWithRVVPadding(MF) -
+                                                RVFI->getVarArgsSaveSize();
   uint64_t RVVStackSize = RVFI->getRVVStackSize();
 
-  // Restore the stack pointer using the value of the frame pointer. Only
-  // necessary if the stack pointer was modified, meaning the stack size is
-  // unknown.
-  //
-  // In order to make sure the stack point is right through the EH region,
-  // we also need to restore stack pointer from the frame pointer if we
-  // don't preserve stack space within prologue/epilogue for outgoing variables,
-  // normally it's just checking the variable sized object is present or not
-  // is enough, but we also don't preserve that at prologue/epilogue when
-  // have vector objects in stack.
-  if (RI->hasStackRealignment(MF) || MFI.hasVarSizedObjects() ||
-      !hasReservedCallFrame(MF)) {
-    assert(hasFP(MF) && "frame pointer should not have been eliminated");
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kito-cheng wrote:

Could you try to keep this assertion in some where if possible?

https://github.com/llvm/llvm-project/pull/110809