[v4] Implement new RTL optimizations pass: fold-mem-offsets.

diff --git a/gcc/Makefile.in b/gcc/Makefile.in
index e99628cec07..d717e90bc44 100644
--- a/gcc/Makefile.in
+++ b/gcc/Makefile.in
@@ -1431,6 +1431,7 @@  OBJS = \
 	fixed-value.o \
 	fold-const.o \
 	fold-const-call.o \
+	fold-mem-offsets.o \
 	function.o \
 	function-abi.o \
 	function-tests.o \
diff --git a/gcc/common.opt b/gcc/common.opt
index 0888c15b88f..5f3d3e9706f 100644
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -1248,6 +1248,10 @@  fcprop-registers
 Common Var(flag_cprop_registers) Optimization
 Perform a register copy-propagation optimization pass.
 
+ffold-mem-offsets
+Target Bool Var(flag_fold_mem_offsets) Init(1)
+Fold instructions calculating memory offsets to the memory access instruction if possible.
+
 fcrossjumping
 Common Var(flag_crossjumping) Optimization
 Perform cross-jumping optimization.
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 674f956f4b8..30974309e9b 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -540,6 +540,7 @@  Objective-C and Objective-C++ Dialects}.
 -fauto-inc-dec  -fbranch-probabilities
 -fcaller-saves
 -fcombine-stack-adjustments  -fconserve-stack
+-ffold-mem-offsets
 -fcompare-elim  -fcprop-registers  -fcrossjumping
 -fcse-follow-jumps  -fcse-skip-blocks  -fcx-fortran-rules
 -fcx-limited-range
@@ -14314,6 +14315,13 @@  the comparison operation before register allocation is complete.
 
 Enabled at levels @option{-O1}, @option{-O2}, @option{-O3}, @option{-Os}.
 
+@opindex ffold-mem-offsets
+@item -ffold-mem-offsets
+@itemx -fno-fold-mem-offsets
+Try to eliminate add instructions by folding them in memory loads/stores.
+
+Enabled at levels @option{-O2}, @option{-O3}.
+
 @opindex fcprop-registers
 @item -fcprop-registers
 After register allocation and post-register allocation instruction splitting,
diff --git a/gcc/fold-mem-offsets.cc b/gcc/fold-mem-offsets.cc
new file mode 100644
index 00000000000..e500fa30002
--- /dev/null
+++ b/gcc/fold-mem-offsets.cc
@@ -0,0 +1,725 @@ 
+/* Late RTL pass to fold memory offsets.
+   Copyright (C) 2023 Free Software Foundation, Inc.
+
+This file is part of GCC.
+
+GCC is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 3, or (at your option)
+any later version.
+
+GCC is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with GCC; see the file COPYING3.  If not see
+<http://www.gnu.org/licenses/>.  */
+
+#include "config.h"
+#include "system.h"
+#include "coretypes.h"
+#include "tm.h"
+#include "rtl.h"
+#include "tree.h"
+#include "expr.h"
+#include "backend.h"
+#include "regs.h"
+#include "target.h"
+#include "memmodel.h"
+#include "emit-rtl.h"
+#include "insn-config.h"
+#include "recog.h"
+#include "predict.h"
+#include "df.h"
+#include "tree-pass.h"
+#include "cfgrtl.h"
+
+/* This pass tries to optimize memory offset calculations by moving constants
+   from add instructions to the memory instructions (loads / stores).
+   For example it can transform code like this:
+
+     add  t4, sp, 16
+     add  t2, a6, t4
+     shl  t3, t2, 1
+     ld   a2, 0(t3)
+     add  a2, 1
+     sd   a2, 8(t2)
+
+   into the following (one instruction less):
+
+     add  t2, a6, sp
+     shl  t3, t2, 1
+     ld   a2, 32(t3)
+     add  a2, 1
+     sd   a2, 24(t2)
+
+   Although the previous passes try to emit efficient offset calculations
+   this pass is still beneficial because:
+
+    - The mechanisms that optimize memory offsets usually work with specific
+      patterns or have limitations.  This pass is designed to fold offsets
+      through complex calculations that affect multiple memory operations
+      and have partially overlapping calculations.
+
+    - There are cases where add instructions are introduced in late rtl passes
+      and the rest of the pipeline cannot eliminate them.  Arrays and structs
+      allocated on the stack can result in unwanted add instructions that
+      cannot be eliminated easily.
+
+   This pass works on a basic block level and consists of 4 phases:
+
+    - Phase 1 (Analysis): Find "foldable" instructions.
+      Foldable instructions are those that we know how to propagate
+      a constant addition through (add, shift, move, ...) and only have other
+      foldable instructions for uses.  In that phase a DFS traversal on the
+      definition tree is performed and foldable instructions are marked on
+      a bitmap.  The add immediate instructions that are reachable in this
+      DFS are candidates for folding since all the intermediate calculations
+      affected by them are also foldable.
+
+    - Phase 2 (Validity): Traverse and calculate the offsets that would result
+      from folding the add immediate instructions.  Check whether the
+      calculated offsets result in a valid instruction for the target.
+
+    - Phase 3 (Commit offsets): Traverse again.  It is now known which folds
+      are valid so at this point change the offsets in the memory instructions.
+
+    - Phase 4 (Commit instruction deletions): Scan all instructions and delete
+      or simplify (reduce to move) all add immediate instructions that were
+      folded.
+
+   This pass should run before hard register propagation because it creates
+   register moves that we expect to be eliminated.  */
+
+namespace {
+
+const pass_data pass_data_fold_mem =
+{
+  RTL_PASS, /* type */
+  "fold_mem_offsets", /* name */
+  OPTGROUP_NONE, /* optinfo_flags */
+  TV_NONE, /* tv_id */
+  0, /* properties_required */
+  0, /* properties_provided */
+  0, /* properties_destroyed */
+  0, /* todo_flags_start */
+  TODO_df_finish, /* todo_flags_finish */
+};
+
+class pass_fold_mem_offsets : public rtl_opt_pass
+{
+public:
+  pass_fold_mem_offsets (gcc::context *ctxt)
+    : rtl_opt_pass (pass_data_fold_mem, ctxt)
+  {}
+
+  /* opt_pass methods: */
+  virtual bool gate (function *)
+    {
+      return flag_fold_mem_offsets && optimize >= 2;
+    }
+
+  virtual unsigned int execute (function *);
+}; // class pass_fold_mem_offsets
+
+/* Tracks which instructions can be reached through instructions that can
+   propagate offsets for folding.  */
+static bitmap_head can_fold_insns;
+
+/* Marks instructions that are currently eligible for folding.  */
+static bitmap_head candidate_fold_insns;
+
+/* Tracks instructions that cannot be folded because it turned out that
+   folding will result in creating an invalid memory instruction.
+   An instruction can be in both CANDIDATE_FOLD_INSNS and CANNOT_FOLD_INSNS
+   at the same time, in which case it is not legal to fold.  */
+static bitmap_head cannot_fold_insns;
+
+/* The number of instructions that were simplified or eliminated.  */
+static int stats_fold_count;
+
+/* Get the single reaching definition of an instruction inside a BB.
+   The definition is desired for REG used in INSN.
+   Return the definition insn or NULL if there's no definition with
+   the desired criteria.  */
+static rtx_insn*
+get_single_def_in_bb (rtx_insn *insn, rtx reg)
+{
+  df_ref use;
+  struct df_link *ref_chain, *ref_link;
+
+  FOR_EACH_INSN_USE (use, insn)
+    {
+      if (GET_CODE (DF_REF_REG (use)) == SUBREG)
+	return NULL;
+      if (REGNO (DF_REF_REG (use)) == REGNO (reg))
+	break;
+    }
+
+  if (!use)
+    return NULL;
+
+  ref_chain = DF_REF_CHAIN (use);
+
+  if (!ref_chain)
+    return NULL;
+
+  for (ref_link = ref_chain; ref_link; ref_link = ref_link->next)
+    {
+      /* Problem getting some definition for this instruction.  */
+      if (ref_link->ref == NULL)
+	return NULL;
+      if (DF_REF_INSN_INFO (ref_link->ref) == NULL)
+	return NULL;
+      if (global_regs[REGNO (reg)]
+	  && !set_of (reg, DF_REF_INSN (ref_link->ref)))
+	return NULL;
+    }
+
+  if (ref_chain->next)
+    return NULL;
+
+  rtx_insn* def = DF_REF_INSN (ref_chain->ref);
+
+  if (BLOCK_FOR_INSN (def) != BLOCK_FOR_INSN (insn))
+    return NULL;
+
+  if (DF_INSN_LUID (def) > DF_INSN_LUID (insn))
+    return NULL;
+
+  return def;
+}
+
+/* Get all uses of REG which is set in INSN.  Return the use list or NULL if a
+   use is missing / irregular.  If SUCCESS is not NULL then set it to false if
+   there are missing / irregular uses and true otherwise.  */
+static struct df_link*
+get_uses (rtx_insn *insn, rtx reg, bool* success)
+{
+  df_ref def;
+  struct df_link *ref_chain, *ref_link;
+
+  if (success)
+    *success = false;
+
+  FOR_EACH_INSN_DEF (def, insn)
+    if (REGNO (DF_REF_REG (def)) == REGNO (reg))
+      break;
+
+  if (!def)
+    return NULL;
+
+  ref_chain = DF_REF_CHAIN (def);
+
+  for (ref_link = ref_chain; ref_link; ref_link = ref_link->next)
+    {
+      /* Problem getting a use for this instruction.  */
+      if (ref_link->ref == NULL)
+	return NULL;
+      if (DF_REF_CLASS (ref_link->ref) != DF_REF_REGULAR)
+	return NULL;
+      /* We do not handle REG_EQUIV/REG_EQ notes for now.  */
+      if (DF_REF_FLAGS (ref_link->ref) & DF_REF_IN_NOTE)
+	return NULL;
+    }
+
+  if (success)
+    *success = true;
+
+  return ref_chain;
+}
+
+/* Function that computes the offset that would have to be added to all uses
+   of REG if the instructions marked in FOLDABLE_INSNS were to be eliminated.
+
+   If ANALYZE is true then mark in CAN_FOLD_INSNS which instructions
+   transitively only affect other instructions found in CAN_FOLD_INSNS.
+   If ANALYZE is false then compute the offset required for folding.  */
+static HOST_WIDE_INT
+fold_offsets (rtx_insn* insn, rtx reg, bool analyze, bitmap foldable_insns)
+{
+  rtx_insn* def = get_single_def_in_bb (insn, reg);
+
+  if (!def || GET_CODE (PATTERN (def)) != SET)
+    return 0;
+
+  rtx src = SET_SRC (PATTERN (def));
+  rtx dest = SET_DEST (PATTERN (def));
+
+  if (!REG_P (dest))
+    return 0;
+
+  enum rtx_code code = GET_CODE (src);
+
+  /* Keep these in sync with the switch below.  We need to early out because
+     otherwise a lot of unnecessary work is done in use analysis.  */
+  if (!(code == PLUS || code == MINUS || code == NEG || code == MULT
+	|| code == ASHIFT || code == REG || code == CONST_INT))
+    return 0;
+
+  unsigned int dest_regno = REGNO (dest);
+
+  /* We can only affect the values of GPR registers.  */
+  if (fixed_regs[dest_regno]
+      || !TEST_HARD_REG_BIT (reg_class_contents[GENERAL_REGS], dest_regno))
+    return 0;
+
+  if (analyze)
+    {
+      /* We only fold through instructions that are transitively used as
+	 memory addresses and do not have other uses.  Use the same logic
+	 from offset calculation to visit instructions that can propagate
+	 offsets and keep track of them in CAN_FOLD_INSNS.  */
+      bool success;
+      struct df_link *uses = get_uses (def, dest, &success), *ref_link;
+
+      if (!success)
+	return 0;
+
+      for (ref_link = uses; ref_link; ref_link = ref_link->next)
+	{
+	  rtx_insn* use = DF_REF_INSN (ref_link->ref);
+
+	  if (DEBUG_INSN_P (use))
+	    continue;
+
+	  /* Punt if the use is anything more complicated than a set
+	     (clobber, use, etc).  */
+	  if (!NONJUMP_INSN_P (use) || GET_CODE (PATTERN (use)) != SET)
+	    return 0;
+
+	  /* This use affects instructions outside of CAN_FOLD_INSNS.  */
+	  if (!bitmap_bit_p (&can_fold_insns, INSN_UID (use)))
+	    return 0;
+
+	  rtx use_set = PATTERN (use);
+
+	  /* Special case: A foldable memory store is not foldable if it
+	     mentions DEST outside of the address calculation.  */
+	  if (use_set && MEM_P (SET_DEST (use_set))
+	      && reg_mentioned_p (dest, SET_SRC (use_set)))
+	    return 0;
+	}
+
+      bitmap_set_bit (&can_fold_insns, INSN_UID (def));
+
+      if (dump_file && (dump_flags & TDF_DETAILS))
+	{
+	  fprintf (dump_file, "Instruction marked for propagation: ");
+	  print_rtl_single (dump_file, def);
+	}
+    }
+  else
+    {
+      /* We cannot propagate through this instruction.  */
+      if (!bitmap_bit_p (&can_fold_insns, INSN_UID (def)))
+	return 0;
+    }
+
+  switch (code)
+    {
+    case PLUS:
+      {
+	/* Propagate through add.  */
+	rtx arg1 = XEXP (src, 0);
+	rtx arg2 = XEXP (src, 1);
+	HOST_WIDE_INT offset = 0;
+
+	if (REG_P (arg1))
+	  offset += fold_offsets (def, arg1, analyze, foldable_insns);
+	else if (GET_CODE (arg1) == ASHIFT
+		 && REG_P (XEXP (arg1, 0))
+		 && CONST_INT_P (XEXP (arg1, 1)))
+	  {
+	    /* Handle R1 = (R2 << C) + ...  */
+	    HOST_WIDE_INT scale
+	      = (HOST_WIDE_INT_1U << INTVAL (XEXP (arg1, 1)));
+	    offset += scale * fold_offsets (def, XEXP (arg1, 0), analyze,
+					 foldable_insns);
+	  }
+	else if (GET_CODE (arg1) == PLUS
+		 && REG_P (XEXP (arg1, 0))
+		 && REG_P (XEXP (arg1, 1)))
+	  {
+	    /* Handle R1 = (R2 + R3) + ...  */
+	    offset += fold_offsets (def, XEXP (arg1, 0), analyze,
+				    foldable_insns);
+	    offset += fold_offsets (def, XEXP (arg1, 1), analyze,
+				    foldable_insns);
+	  }
+	else if (GET_CODE (arg1) == PLUS
+		 && GET_CODE (XEXP (arg1, 0)) == ASHIFT
+		 && REG_P (XEXP (XEXP (arg1, 0), 0))
+		 && CONST_INT_P (XEXP (XEXP (arg1, 0), 1))
+		 && REG_P (XEXP (arg1, 1)))
+	  {
+	    /* Handle R1 = ((R2 << C) + R3) + ...  */
+	    HOST_WIDE_INT scale
+	      = (HOST_WIDE_INT_1U << INTVAL (XEXP (XEXP (arg1, 0), 1)));
+	    offset += scale * fold_offsets (def, XEXP (XEXP (arg1, 0), 0),
+					    analyze, foldable_insns);
+	    offset += fold_offsets (def, XEXP (arg1, 1), analyze,
+				    foldable_insns);
+	  }
+	else
+	  return 0;
+
+	if (REG_P (arg2))
+	  offset += fold_offsets (def, arg2, analyze, foldable_insns);
+	else if (REG_P (arg1) && CONST_INT_P (arg2) && !analyze)
+	  {
+	    offset += INTVAL (arg2);
+	    /* This is a R1 = R2 + C instruction, candidate for folding.  */
+	    bitmap_set_bit (foldable_insns, INSN_UID (def));
+	  }
+	else
+	  return 0;
+
+	return offset;
+      }
+    case MINUS:
+      {
+	/* Propagate through minus.  */
+	rtx arg1 = XEXP (src, 0);
+	rtx arg2 = XEXP (src, 1);
+	HOST_WIDE_INT offset = 0;
+
+	if (REG_P (arg1))
+	  offset += fold_offsets (def, arg1, analyze, foldable_insns);
+	else
+	  return 0;
+
+	if (REG_P (arg2))
+	  offset -= fold_offsets (def, arg2, analyze, foldable_insns);
+	else if (REG_P (arg1) && CONST_INT_P (arg2) && !analyze)
+	  {
+	    offset -= INTVAL (arg2);
+	    /* This is a R1 = R2 - C instruction, candidate for folding.  */
+	    bitmap_set_bit (foldable_insns, INSN_UID (def));
+	  }
+	else
+	  return 0;
+
+	return offset;
+      }
+    case NEG:
+      {
+	/* Propagate through negation.  */
+	rtx arg1 = XEXP (src, 0);
+	if (REG_P (arg1))
+	  return -fold_offsets (def, arg1, analyze, foldable_insns);
+	else
+	  return 0;
+      }
+    case MULT:
+      {
+	/* Propagate through multiply by constant.  */
+	rtx arg1 = XEXP (src, 0);
+	rtx arg2 = XEXP (src, 1);
+
+	if (REG_P (arg1) && CONST_INT_P (arg2))
+	  {
+	    HOST_WIDE_INT scale = INTVAL (arg2);
+	    return scale * fold_offsets (def, arg1, analyze, foldable_insns);
+	  }
+
+	return 0;
+      }
+    case ASHIFT:
+      {
+	/* Propagate through shift left by constant.  */
+	rtx arg1 = XEXP (src, 0);
+	rtx arg2 = XEXP (src, 1);
+
+	if (REG_P (arg1) && CONST_INT_P (arg2))
+	  {
+	    HOST_WIDE_INT scale = (HOST_WIDE_INT_1U << INTVAL (arg2));
+	    return scale * fold_offsets (def, arg1, analyze, foldable_insns);
+	  }
+
+	return 0;
+      }
+    case REG:
+      /* Propagate through register move.  */
+      return fold_offsets (def, src, analyze, foldable_insns);
+    case CONST_INT:
+      {
+	/* R1 = C is candidate for folding.  */
+	if (!analyze)
+	  bitmap_set_bit (foldable_insns, INSN_UID (def));
+	return INTVAL (src);
+      }
+    default:
+      /* Cannot propagate.  */
+      return 0;
+    }
+}
+
+/* Test if INSN is a memory load / store that can have an offset folded to it.
+   Return true iff INSN is such an instruction and return through MEM_OUT,
+   REG_OUT and OFFSET_OUT the RTX that has a MEM code, the register that is
+   used as a base address and the offset accordingly.
+   All of the out pointers may be NULL in which case they will be ignored.  */
+bool
+get_fold_mem_root (rtx_insn* insn, rtx *mem_out, rtx *reg_out,
+		   HOST_WIDE_INT *offset_out)
+{
+  rtx set = single_set (insn);
+  rtx mem = NULL_RTX;
+
+  if (set != NULL_RTX)
+    {
+      rtx src = SET_SRC (set);
+      rtx dest = SET_DEST (set);
+
+      /* Don't fold when we have unspec / volatile.  */
+      if (GET_CODE (src) == UNSPEC
+	  || GET_CODE (src) == UNSPEC_VOLATILE
+	  || GET_CODE (dest) == UNSPEC
+	  || GET_CODE (dest) == UNSPEC_VOLATILE)
+	return false;
+
+      if (MEM_P (src))
+	mem = src;
+      else if (MEM_P (dest))
+	mem = dest;
+      else if ((GET_CODE (src) == SIGN_EXTEND
+		|| GET_CODE (src) == ZERO_EXTEND)
+	       && MEM_P (XEXP (src, 0)))
+	mem = XEXP (src, 0);
+    }
+
+  if (mem == NULL_RTX)
+    return false;
+
+  rtx mem_addr = XEXP (mem, 0);
+  rtx reg;
+  HOST_WIDE_INT offset;
+
+  if (REG_P (mem_addr))
+    {
+      reg = mem_addr;
+      offset = 0;
+    }
+  else if (GET_CODE (mem_addr) == PLUS
+	   && REG_P (XEXP (mem_addr, 0))
+	   && CONST_INT_P (XEXP (mem_addr, 1)))
+    {
+      reg = XEXP (mem_addr, 0);
+      offset = INTVAL (XEXP (mem_addr, 1));
+    }
+  else
+    return false;
+
+  if (mem_out)
+    *mem_out = mem;
+  if (reg_out)
+    *reg_out = reg;
+  if (offset_out)
+    *offset_out = offset;
+
+  return true;
+}
+
+/* If INSN is a root memory instruction then do a DFS traversal on its
+   definitions and find folding candidates.  */
+static void
+do_analysis (rtx_insn* insn)
+{
+  rtx reg;
+  if (!get_fold_mem_root (insn, NULL, &reg, NULL))
+    return;
+
+  if (dump_file && (dump_flags & TDF_DETAILS))
+    {
+      fprintf (dump_file, "Starting analysis from root: ");
+      print_rtl_single (dump_file, insn);
+    }
+
+  /* Analyse folding opportunities for this memory instruction.  */
+  bitmap_set_bit (&can_fold_insns, INSN_UID (insn));
+  fold_offsets (insn, reg, true, NULL);
+}
+
+/* If INSN is a root memory instruction then compute a potentially new offset
+   for it and test if the resulting instruction is valid.  */
+static void
+do_check_validity (rtx_insn* insn)
+{
+  rtx mem, reg;
+  HOST_WIDE_INT cur_offset;
+  if (!get_fold_mem_root (insn, &mem, &reg, &cur_offset))
+    return;
+
+  auto_bitmap fold_insns;
+  HOST_WIDE_INT new_offset
+    = cur_offset + fold_offsets (insn, reg, false, fold_insns);
+
+  /* Test if it is valid to change MEM's address offset to NEW_OFFSET.  */
+  int icode = INSN_CODE (insn);
+  rtx mem_addr = XEXP (mem, 0);
+  machine_mode mode = GET_MODE (mem_addr);
+  XEXP (mem, 0) = gen_rtx_PLUS (mode, reg, gen_int_mode (new_offset, mode));
+
+  bool illegal = insn_invalid_p (insn, false)
+		 || !memory_address_addr_space_p (mode, XEXP (mem, 0),
+						  MEM_ADDR_SPACE (mem));
+
+  /* Restore the instruction.  */
+  XEXP (mem, 0) = mem_addr;
+  INSN_CODE (insn) = icode;
+
+  if (illegal)
+    bitmap_ior_into (&cannot_fold_insns, fold_insns);
+  else
+    bitmap_ior_into (&candidate_fold_insns, fold_insns);
+}
+
+/* If INSN is a root memory instruction that was affected by any folding
+   then update its offset as necessary.  */
+static void
+do_commit_offset (rtx_insn* insn)
+{
+  rtx mem, reg;
+  HOST_WIDE_INT cur_offset;
+  if (!get_fold_mem_root (insn, &mem, &reg, &cur_offset))
+    return;
+
+  auto_bitmap fold_insns;
+  HOST_WIDE_INT new_offset
+    = cur_offset + fold_offsets (insn, reg, false, fold_insns);
+
+  /* If an change turned out illegal in the previous phase then legal
+     transformations that share calculations also become illegal.  */
+  if (bitmap_intersect_p (&cannot_fold_insns, fold_insns))
+    {
+      bitmap_ior_into (&cannot_fold_insns, fold_insns);
+      return;
+    }
+
+  if (new_offset == cur_offset)
+    return;
+
+  if (dump_file)
+    {
+      fprintf (dump_file, "Memory offset changed from "
+	       HOST_WIDE_INT_PRINT_DEC " to " HOST_WIDE_INT_PRINT_DEC
+	       " for instruction:\n", cur_offset, new_offset);
+      print_rtl_single (dump_file, insn);
+    }
+
+  gcc_assert (!bitmap_empty_p (fold_insns));
+  machine_mode mode = GET_MODE (XEXP (mem, 0));
+  XEXP (mem, 0) = gen_rtx_PLUS (mode, reg, gen_int_mode (new_offset, mode));
+  INSN_CODE (insn) = recog (PATTERN (insn), insn, 0);
+  df_insn_rescan (insn);
+}
+
+/* If INSN is a move / add instruction that was folded then replace its
+   constant part with zero.  */
+static void
+do_commit_insn (rtx_insn* insn)
+{
+  if (bitmap_bit_p (&candidate_fold_insns, INSN_UID (insn))
+      && !bitmap_bit_p (&cannot_fold_insns, INSN_UID (insn)))
+    {
+      if (dump_file)
+	{
+	  fprintf (dump_file, "Instruction folded:");
+	  print_rtl_single (dump_file, insn);
+	}
+
+      stats_fold_count++;
+
+      rtx set = single_set (insn);
+      rtx dest = SET_DEST (set);
+      rtx src = SET_SRC (set);
+
+      /* Emit a move and let subsequent passes eliminate it if possible.  */
+      if (GET_CODE (src) == CONST_INT)
+	{
+	  /* INSN is R1 = C.
+	     Replace it with R1 = 0 because C was folded.  */
+	  rtx mov_rtx
+	    = gen_move_insn (dest, gen_int_mode (0, GET_MODE (dest)));
+	  df_insn_rescan (emit_insn_after (mov_rtx, insn));
+	}
+      else
+	{
+	  /* INSN is R1 = R2 + C.
+	     Replace it with R1 = R2 because C was folded.  */
+	  rtx arg1 = XEXP (src, 0);
+
+	  /* If the DEST == ARG1 then the move is a no-op.  */
+	  if (REGNO (dest) != REGNO (arg1))
+	    {
+	      gcc_checking_assert (GET_MODE (dest) == GET_MODE (arg1));
+	      rtx mov_rtx = gen_move_insn (dest, arg1);
+	      df_insn_rescan (emit_insn_after (mov_rtx, insn));
+	    }
+	}
+
+      /* Delete the original move / add instruction.  */
+      delete_insn (insn);
+    }
+}
+
+unsigned int
+pass_fold_mem_offsets::execute (function *fn)
+{
+  df_set_flags (DF_EQ_NOTES + DF_RD_PRUNE_DEAD_DEFS + DF_DEFER_INSN_RESCAN);
+  df_chain_add_problem (DF_UD_CHAIN + DF_DU_CHAIN);
+  df_analyze ();
+
+  bitmap_initialize (&can_fold_insns, NULL);
+  bitmap_initialize (&candidate_fold_insns, NULL);
+  bitmap_initialize (&cannot_fold_insns, NULL);
+
+  stats_fold_count = 0;
+
+  basic_block bb;
+  rtx_insn *insn;
+  FOR_ALL_BB_FN (bb, fn)
+    {
+      /* There is a conflict between this pass and RISCV's shorten-memrefs
+	  pass.  For now disable folding if optimizing for size because
+	  otherwise this cancels the effects of shorten-memrefs.  */
+      if (optimize_bb_for_size_p (bb))
+	continue;
+
+      bitmap_clear (&can_fold_insns);
+      bitmap_clear (&candidate_fold_insns);
+      bitmap_clear (&cannot_fold_insns);
+
+      FOR_BB_INSNS (bb, insn)
+	do_analysis (insn);
+
+      FOR_BB_INSNS (bb, insn)
+	do_check_validity (insn);
+
+      FOR_BB_INSNS (bb, insn)
+	do_commit_offset (insn);
+
+      FOR_BB_INSNS (bb, insn)
+	do_commit_insn (insn);
+    }
+
+  statistics_counter_event (cfun, "Number of folded instructions",
+			    stats_fold_count);
+
+  bitmap_release (&can_fold_insns);
+  bitmap_release (&candidate_fold_insns);
+  bitmap_release (&cannot_fold_insns);
+
+  return 0;
+}
+
+} // anon namespace
+
+rtl_opt_pass *
+make_pass_fold_mem_offsets (gcc::context *ctxt)
+{
+  return new pass_fold_mem_offsets (ctxt);
+}
diff --git a/gcc/passes.def b/gcc/passes.def
index ef5a21afe49..4a0e9a1aee2 100644
--- a/gcc/passes.def
+++ b/gcc/passes.def
@@ -516,6 +516,7 @@  along with GCC; see the file COPYING3.  If not see
 	  NEXT_PASS (pass_peephole2);
 	  NEXT_PASS (pass_if_after_reload);
 	  NEXT_PASS (pass_regrename);
+	  NEXT_PASS (pass_fold_mem_offsets);
 	  NEXT_PASS (pass_cprop_hardreg);
 	  NEXT_PASS (pass_fast_rtl_dce);
 	  NEXT_PASS (pass_reorder_blocks);
diff --git a/gcc/testsuite/gcc.target/riscv/fold-mem-offsets-1.c b/gcc/testsuite/gcc.target/riscv/fold-mem-offsets-1.c
new file mode 100644
index 00000000000..574cc92b6ab
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/fold-mem-offsets-1.c
@@ -0,0 +1,16 @@ 
+/* { dg-do compile } */
+/* { dg-options "-O2 -mfold-mem-offsets" } */
+
+void sink(int arr[2]);
+
+void
+foo(int a, int b, int i)
+{
+  int arr[2] = {a, b};
+  arr[i]++;
+  sink(arr);
+}
+
+// Should compile without negative memory offsets when using -mfold-mem-offsets
+/* { dg-final { scan-assembler-not "lw\t.*,-.*\\(.*\\)" } } */
+/* { dg-final { scan-assembler-not "sw\t.*,-.*\\(.*\\)" } } */
\ No newline at end of file
diff --git a/gcc/testsuite/gcc.target/riscv/fold-mem-offsets-2.c b/gcc/testsuite/gcc.target/riscv/fold-mem-offsets-2.c
new file mode 100644
index 00000000000..e6c251d3a3c
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/fold-mem-offsets-2.c
@@ -0,0 +1,24 @@ 
+/* { dg-do compile } */
+/* { dg-options "-O2 -mfold-mem-offsets" } */
+
+void sink(int arr[3]);
+
+void
+foo(int a, int b, int c, int i)
+{
+  int arr1[3] = {a, b, c};
+  int arr2[3] = {a, c, b};
+  int arr3[3] = {c, b, a};
+
+  arr1[i]++;
+  arr2[i]++;
+  arr3[i]++;
+  
+  sink(arr1);
+  sink(arr2);
+  sink(arr3);
+}
+
+// Should compile without negative memory offsets when using -mfold-mem-offsets
+/* { dg-final { scan-assembler-not "lw\t.*,-.*\\(.*\\)" } } */
+/* { dg-final { scan-assembler-not "sw\t.*,-.*\\(.*\\)" } } */
\ No newline at end of file
diff --git a/gcc/testsuite/gcc.target/riscv/fold-mem-offsets-3.c b/gcc/testsuite/gcc.target/riscv/fold-mem-offsets-3.c
new file mode 100644
index 00000000000..8586d3e3a29
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/fold-mem-offsets-3.c
@@ -0,0 +1,17 @@ 
+/* { dg-do compile } */
+/* { dg-options "-O2 -mfold-mem-offsets" } */
+
+void load(int arr[2]);
+
+int
+foo(long unsigned int i)
+{
+  int arr[2];
+  load(arr);
+
+  return arr[3 * i + 77];
+}
+
+// Should compile without negative memory offsets when using -mfold-mem-offsets
+/* { dg-final { scan-assembler-not "lw\t.*,-.*\\(.*\\)" } } */
+/* { dg-final { scan-assembler-not "addi\t.*,.*,77" } } */
\ No newline at end of file
diff --git a/gcc/tree-pass.h b/gcc/tree-pass.h
index 57865cdfc42..69a8a6d5cb7 100644
--- a/gcc/tree-pass.h
+++ b/gcc/tree-pass.h
@@ -618,6 +618,7 @@  extern rtl_opt_pass *make_pass_sched_fusion (gcc::context *ctxt);
 extern rtl_opt_pass *make_pass_peephole2 (gcc::context *ctxt);
 extern rtl_opt_pass *make_pass_if_after_reload (gcc::context *ctxt);
 extern rtl_opt_pass *make_pass_regrename (gcc::context *ctxt);
+extern rtl_opt_pass *make_pass_fold_mem_offsets (gcc::context *ctxt);
 extern rtl_opt_pass *make_pass_cprop_hardreg (gcc::context *ctxt);
 extern rtl_opt_pass *make_pass_reorder_blocks (gcc::context *ctxt);
 extern rtl_opt_pass *make_pass_leaf_regs (gcc::context *ctxt);