[gcc r17-3191] i386: Split MOVBE alternatives out of *bswaphi2_movbe to drop flags clobber

https://gcc.gnu.org/g:a7a008375aaacb658bca0b57157366778a369ddf

commit r17-3191-ga7a008375aaacb658bca0b57157366778a369ddf
Author: Uros Bizjak <[email protected]>
Date:   Mon Aug 10 09:58:11 2026 +0200

    i386: Split MOVBE alternatives out of *bswaphi2_movbe to drop flags clobber
    
    The MOVBE alternatives in *bswaphi2_movbe carry a
    (clobber (reg:CC FLAGS_REG)) that only the ROL alternative
    sharing the pattern actually needs. MOVBE does not touch
    EFLAGS, so once reload has picked an alternative, split the
    MOVBE cases out into a new clobber-free *movbehi2 pattern.
    
    gcc/ChangeLog:
    
            * config/i386/i386.md (*movbehi2): New insn, split from the
            movbe alternatives of *bswaphi2_movbe.
            (*bswaphi2_movbe): Convert to define_insn_and_split.  Split
            the MOVBE alternatives (mem<->reg) post-reload into *movbehi2
            to drop the now-unneeded flags clobber.

Diff:
---
 gcc/config/i386/i386.md | 25 ++++++++++++++++++++++---
 1 file changed, 22 insertions(+), 3 deletions(-)

diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
index 3b0f8b2cccd3..73d005ef5ed5 100644
--- a/gcc/config/i386/i386.md
+++ b/gcc/config/i386/i386.md
@@ -23658,7 +23658,21 @@
     operands[1] = force_reg (HImode, operands[1]);
 })
 
-(define_insn "*bswaphi2_movbe"
+(define_insn "*movbehi2"
+  [(set (match_operand:HI 0 "nonimmediate_operand" "=r,m")
+	(bswap:HI (match_operand:HI 1 "nonimmediate_operand" "m,r")))]
+  "TARGET_MOVBE
+   && MEM_P (operands[0]) != MEM_P (operands[1])
+   && reload_completed"
+  "movbe{w}\t{%1, %0|%0, %1}"
+  [(set_attr "type" "imov")
+   (set_attr "modrm" "1")
+   (set_attr "prefix_0f" "1")
+   (set_attr "prefix_extra" "1")
+   (set_attr "mode" "HI")])
+
+;; Convert movbe to avoid flags dependency.
+(define_insn_and_split "*bswaphi2_movbe"
   [(set (match_operand:HI 0 "nonimmediate_operand" "=Q,r,r,m")
 	(bswap:HI (match_operand:HI 1 "nonimmediate_operand" "0,0,m,r")))
    (clobber (reg:CC FLAGS_REG))]
@@ -23667,8 +23681,13 @@
   "@
     xchg{b}\t{%h0, %b0|%b0, %h0}
     rol{w}\t{$8, %0|%0, 8}
-    movbe{w}\t{%1, %0|%0, %1}
-    movbe{w}\t{%1, %0|%0, %1}"
+    #
+    #"
+  "&& MEM_P (operands[0]) != MEM_P (operands[1])
+   && reload_completed"
+  [(set (match_dup 0)
+	(bswap:HI (match_dup 1)))]
+  ""
   [(set_attr "type" "imov,rotate1,imov,imov")
    (set_attr "modrm" "*,*,1,1")
    (set_attr "prefix_0f" "*,*,1,1")