From 73eb0027ef4c4a85b9233a37a2e281f1222b1f90 Mon Sep 17 00:00:00 2001
From: Lulu Cheng <chenglulu@loongson.cn>
Date: Thu, 30 Oct 2025 11:16:32 +0800
Subject: [PATCH] LoongArch: When loading an immediate value, promote mode to
 word_mode.

This optimization can eliminate redundant immediate load instructions
during CSE optimization.

gcc/ChangeLog:

	* config/loongarch/loongarch.cc
	(loongarch_legitimize_move): Optimize.

gcc/testsuite/ChangeLog:

	* gcc.target/loongarch/sign-extend-6.c: New test.
---
 gcc/config/loongarch/loongarch.cc               | 15 ++++++++++++++-
 .../gcc.target/loongarch/sign-extend-6.c        | 17 +++++++++++++++++
 2 files changed, 31 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/gcc.target/loongarch/sign-extend-6.c

diff --git a/gcc/config/loongarch/loongarch.cc b/gcc/config/loongarch/loongarch.cc
index d11fe496a01..4e53635a7b9 100644
--- a/gcc/config/loongarch/loongarch.cc
+++ b/gcc/config/loongarch/loongarch.cc
@@ -3534,7 +3534,20 @@ loongarch_legitimize_move (machine_mode mode, rtx dest, rtx src)
 {
   if (!register_operand (dest, mode) && !reg_or_0_operand (src, mode))
     {
-      loongarch_emit_move (dest, force_reg (mode, src));
+      /* When loading fixed-point scalar data, if the size of the mode
+	 is smaller than the size of `word_mode`, the immediate value
+	 is first loaded into a register of type `word_mode`.
+	 This facilitates the elimination of common self-expressions.
+	 This reduces redundant immediate value loading instructions.  */
+      rtx tmp;
+      if (GET_MODE_CLASS (mode) == MODE_INT
+	  && GET_CODE (src) == CONST_INT
+	  && GET_MODE_SIZE (mode) < UNITS_PER_WORD)
+	tmp = gen_lowpart (mode, force_reg (word_mode, src));
+      else
+	tmp = force_reg (mode, src);
+
+      loongarch_emit_move (dest, tmp);
       return true;
     }
 
diff --git a/gcc/testsuite/gcc.target/loongarch/sign-extend-6.c b/gcc/testsuite/gcc.target/loongarch/sign-extend-6.c
new file mode 100644
index 00000000000..74d0e589b1e
--- /dev/null
+++ b/gcc/testsuite/gcc.target/loongarch/sign-extend-6.c
@@ -0,0 +1,17 @@
+/* { dg-do compile } */
+/* { dg-options "-mabi=lp64d -O2" } */
+/* { dg-final { scan-assembler-times "addi.w\t\\\$r\[0-9\]+,\\\$r\[0-9\]+,1\t" 1 } } */
+
+extern unsigned short d;
+int
+test (int a, unsigned short b)
+{
+  if (a > 0)
+    {
+      d = 1;
+      if (b > d)
+       return 10;
+    }
+
+  return 50;
+}
-- 
2.47.3