commit 16ed2601
Author: H.J. Lu <hongjiu.lu@intel.com>
Date:   Wed May 15 15:26:19 2019 +0000

    i386: Emulate MMX pshufb with SSE version

has

+(define_insn_and_split "ssse3_pshufbv8qi3"
+  [(set (match_operand:V8QI 0 "register_operand" "=y,x,Yv")
+  (unspec:V8QI [(match_operand:V8QI 1 "register_operand" "0,0,Yv")
+           (match_operand:V8QI 2 "register_mmxmem_operand" "ym,x,Yv")]
+          UNSPEC_PSHUFB))
+   (clobber (match_scratch:V4SI 3 "=X,x,Yv"))]
                                       ^^^  There are earlyclobber.
+  "(TARGET_MMX || TARGET_MMX_WITH_SSE) && TARGET_SSSE3"
+  "@
+   pshufb\t{%2, %0|%0, %2}
+   #
+   #"
+  "TARGET_MMX_WITH_SSE && reload_completed"
+  [(set (match_dup 3) (match_dup 5))
+   (set (match_dup 3)
+  (and:V4SI (match_dup 3) (match_dup 2)))
+   (set (match_dup 0)
+  (unspec:V16QI [(match_dup 1) (match_dup 4)] UNSPEC_PSHUFB))]

If input register operand 2 is dead after this insn, RA may choose it
as scratch operand.  Since it isn't marked as earlyclobber, operand 2
becomes unused after split and then it gets optimized out.  Mark scratch
operand as earlyclobber fixes the issue.

gcc/

	PR target/94467
	* config/i386/sse.md (ssse3_pshufbv8qi3): Mark scratch operand
	as earlyclobber.

gcc/testsuite/

	PR target/94467
	* gcc.target/i386/pr94467-1.c: New test.
	* gcc.target/i386/pr94467-2.c: Likewise.