From: Jeff Law <jlaw@localhost.localdomain>
Date: Tue, 20 Jul 2021 18:49:54 +0000 (-0400)
Subject: Attach MEM_EXPR information when flushing BLKmode args to the stack - V2
X-Git-Tag: basepoints/gcc-13~5894
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=818203714e8640ce29c886b5060c91b12ad3a7c4;p=thirdparty%2Fgcc.git

Attach MEM_EXPR information when flushing BLKmode args to the stack - V2

gcc/
	* function.c (assign_parm_setup_block): Use adjust_address instead
	of change_address to preserve MEM_EXPR and friends.
---

diff --git a/gcc/function.c b/gcc/function.c
index 00b2fe70c7d0..af3d57b32a36 100644
--- a/gcc/function.c
+++ b/gcc/function.c
@@ -3036,7 +3036,15 @@ assign_parm_setup_block (struct assign_parm_data_all *all,
 		  reg = gen_rtx_REG (word_mode, REGNO (entry_parm));
 		  reg = convert_to_mode (mode, copy_to_reg (reg), 1);
 		}
-	      emit_move_insn (change_address (mem, mode, 0), reg);
+
+	      /* We use adjust_address to get a new MEM with the mode
+		 changed.  adjust_address is better than change_address
+		 for this purpose because adjust_address does not lose
+		 the MEM_EXPR associated with the MEM.
+
+		 If the MEM_EXPR is lost, then optimizations like DSE
+		 assume the MEM escapes and thus is not subject to DSE.  */
+	      emit_move_insn (adjust_address (mem, mode, 0), reg);
 	    }
 
 #ifdef BLOCK_REG_PADDING