x86: suppress LEA optimization in a specific 16-bit case

In 16-bit mode a 16-bit address size LEA with a 16-bit displacement and
a 32-bit destination is shorter to encode than the corresponding MOV.
Commit fe134c656991 ("x86: optimize LEA")'s promise was to only do the
transformation when the encoding size wouldn't grow, i.e. it did go a
little too far. Restrict this specific case of the transformation to
-O2.

5 files changed, 69 insertions, 3 deletions

diff --git a/gas/ChangeLog b/gas/ChangeLog
index f07ece7..7133c37 100644
--- a/gas/ChangeLog
+++ b/gas/ChangeLog
@@ -1,3 +1,11 @@
+2021-06-10  Jan Beulich  <jbeulich@suse.com>
+
+	* config/tc-i386.c (optimize_encoding): Suppress LEA conversion
+	when it would grow code size in 16-bit mode.
+	* testsuite/gas/i386/lea16-optimize.d: Adjust expectations.
+	* testsuite/gas/i386/lea16-optimize2.d: New.
+	* testsuite/gas/i386/i386.exp: Run new test.
+
 2021-06-08  Jan Beulich  <jbeulich@suse.com>
 
 	* testsuite/gas/i386/quoted.d, testsuite/gas/i386/wrap32-text.d:
diff --git a/gas/config/tc-i386.c b/gas/config/tc-i386.c
index 80b7098..47c12b9 100644
--- a/gas/config/tc-i386.c
+++ b/gas/config/tc-i386.c
@@ -4140,6 +4140,13 @@ optimize_encoding (void)
 			   ? i.op[1].regs->reg_type.bitfield.dword
 			   : i.op[1].regs->reg_type.bitfield.word)))
 	    return;
+	  /* In 16-bit mode converting LEA with 16-bit addressing and a 32-bit
+	     destination is going to grow encoding size.  */
+	  else if (flag_code == CODE_16BIT
+		   && (optimize <= 1 || optimize_for_space)
+		   && !i.prefix[ADDR_PREFIX]
+		   && i.op[1].regs->reg_type.bitfield.dword)
+	    return;
 	  else
 	    {
 	      i.tm.base_opcode = 0xb8;
diff --git a/gas/testsuite/gas/i386/i386.exp b/gas/testsuite/gas/i386/i386.exp
index ff88bae..cf21511 100644
--- a/gas/testsuite/gas/i386/i386.exp
+++ b/gas/testsuite/gas/i386/i386.exp
@@ -544,6 +544,7 @@ if [gas_32_check] then {
     run_list_test "optimize-7" "-I${srcdir}/$subdir -march=+noavx2 -al"
     run_dump_test "lea-optimize"
     run_dump_test "lea16-optimize"
+    run_dump_test "lea16-optimize2"
     run_dump_test "align-branch-1a"
     run_dump_test "align-branch-1b"
     run_dump_test "align-branch-1c"
diff --git a/gas/testsuite/gas/i386/lea16-optimize.d b/gas/testsuite/gas/i386/lea16-optimize.d
index 3c43b6c..be30758 100644
--- a/gas/testsuite/gas/i386/lea16-optimize.d
+++ b/gas/testsuite/gas/i386/lea16-optimize.d
@@ -31,9 +31,9 @@ Disassembly of section .text:
 [ 	]*[0-9a-f]+:[ 	]+8b f6[ 	]+mov[ 	]+%si,%si
 [ 	]*[0-9a-f]+:[ 	]+66 8b c9[ 	]+mov[ 	]+%ecx,%ecx
 [ 	]*[0-9a-f]+:[ 	]+66 8b c1[ 	]+mov[ 	]+%ecx,%eax
-[ 	]*[0-9a-f]+:[ 	]+66 b8 01 00 00 00[ 	]+mov[ 	]+\$0x1,%eax
+[ 	]*[0-9a-f]+:[ 	]+66 8d 06 01 00[ 	]+lea[ 	]+0x1,%eax
 [ 	]*[0-9a-f]+:[ 	]+b8 02 00[ 	]+mov[ 	]+\$0x2,%ax
-[ 	]*[0-9a-f]+:[ 	]+66 b8 ff ff 00 00[ 	]+mov[ 	]+\$0xffff,%eax
+[ 	]*[0-9a-f]+:[ 	]+66 8d 06 ff ff[ 	]+lea[ 	]+-0x1,%eax
 [ 	]*[0-9a-f]+:[ 	]+b8 fe ff[ 	]+mov[ 	]+\$0xfffe,%ax
 [ 	]*[0-9a-f]+:[ 	]+66 b8 01 00 00 00[ 	]+mov[ 	]+\$0x1,%eax
 [ 	]*[0-9a-f]+:[ 	]+b8 02 00[ 	]+mov[ 	]+\$0x2,%ax
@@ -43,7 +43,7 @@ Disassembly of section .text:
 [ 	]*[0-9a-f]+:[ 	]+b8 00 00[ 	]+mov[ 	]+\$0x0,%ax
 [ 	]*[0-9a-f]+:[ 	]+66 b8 00 00 00 00[ 	]+mov[ 	]+\$0x0,%eax
 [ 	]*[0-9a-f]+:[ 	]+67 8d 05 00 00 00 00[ 	]+addr32 lea[ 	]+0x0,%ax
-[ 	]*[0-9a-f]+:[ 	]+66 b8 00 00 00 00[ 	]+mov[ 	]+\$0x0,%eax
+[ 	]*[0-9a-f]+:[ 	]+66 8d 06 00 00[ 	]+lea[ 	]+0x0,%eax
 [ 	]*[0-9a-f]+:[ 	]+b8 00 00[ 	]+mov[ 	]+\$0x0,%ax
 [ 	]*[0-9a-f]+:[ 	]+8d 47 ff[ 	]+lea[ 	]+-0x1\(%bx\),%ax
 [ 	]*[0-9a-f]+:[ 	]+8d 87 01 00[ 	]+lea[ 	]+0x1\(%bx\),%ax
diff --git a/gas/testsuite/gas/i386/lea16-optimize2.d b/gas/testsuite/gas/i386/lea16-optimize2.d
new file mode 100644
index 0000000..d95f9ac
--- /dev/null
+++ b/gas/testsuite/gas/i386/lea16-optimize2.d
@@ -0,0 +1,50 @@
+#as: -O2 -q -I${srcdir}/$subdir
+#objdump: -dw -Mi8086
+#name: i386 16-bit LEA optimizations at -O2
+#source: lea16.s
+
+.*: +file format .*
+
+Disassembly of section .text:
+
+0+ <start>:
+[ 	]*[0-9a-f]+:[ 	]+67 66 8d 04 08[ 	]+lea[ 	]+\(%eax,%ecx(,1)?\),%eax
+[ 	]*[0-9a-f]+:[ 	]+67 66 8d 04 08[ 	]+lea[ 	]+\(%eax,%ecx(,1)?\),%eax
+[ 	]*[0-9a-f]+:[ 	]+67 66 8d 48 01[ 	]+lea[ 	]+0x1\(%eax\),%ecx
+[ 	]*[0-9a-f]+:[ 	]+67 66 8d 88 00 00 00 00[ 	]+lea[ 	]+0x0\(%eax\),%ecx
+[ 	]*[0-9a-f]+:[ 	]+67 66 8d 0c 25 00 00 00 00[ 	]+addr32 lea[ 	]+0x0,%ecx
+[ 	]*[0-9a-f]+:[ 	]+67 66 8d 04 00[ 	]+lea[ 	]+\(%eax,%eax(,1)?\),%eax
+[ 	]*[0-9a-f]+:[ 	]+67 66 8d 04 45 00 00 00 00[ 	]+lea[ 	]+0x0\(,%eax,2\),%eax
+[ 	]*[0-9a-f]+:[ 	]+67 66 8d 04 25 00 00 00 00[ 	]+addr32 lea[ 	]+0x0,%eax
+[ 	]*[0-9a-f]+:[ 	]+66 8d 00[ 	]+lea[ 	]+\(%bx,%si\),%eax
+[ 	]*[0-9a-f]+:[ 	]+66 8b c0[ 	]+mov[ 	]+%eax,%eax
+[ 	]*[0-9a-f]+:[ 	]+66 8b c8[ 	]+mov[ 	]+%eax,%ecx
+[ 	]*[0-9a-f]+:[ 	]+66 8b c8[ 	]+mov[ 	]+%eax,%ecx
+[ 	]*[0-9a-f]+:[ 	]+66 8b c8[ 	]+mov[ 	]+%eax,%ecx
+[ 	]*[0-9a-f]+:[ 	]+66 8d 04[ 	]+lea[ 	]+\(%si\),%eax
+[ 	]*[0-9a-f]+:[ 	]+66 8d 34[ 	]+lea[ 	]+\(%si\),%esi
+[ 	]*[0-9a-f]+:[ 	]+66 8d 04[ 	]+lea[ 	]+\(%si\),%eax
+[ 	]*[0-9a-f]+:[ 	]+8b c0[ 	]+mov[ 	]+%ax,%ax
+[ 	]*[0-9a-f]+:[ 	]+8b c8[ 	]+mov[ 	]+%ax,%cx
+[ 	]*[0-9a-f]+:[ 	]+8b c8[ 	]+mov[ 	]+%ax,%cx
+[ 	]*[0-9a-f]+:[ 	]+8b c6[ 	]+mov[ 	]+%si,%ax
+[ 	]*[0-9a-f]+:[ 	]+8b f6[ 	]+mov[ 	]+%si,%si
+[ 	]*[0-9a-f]+:[ 	]+66 8b c9[ 	]+mov[ 	]+%ecx,%ecx
+[ 	]*[0-9a-f]+:[ 	]+66 8b c1[ 	]+mov[ 	]+%ecx,%eax
+[ 	]*[0-9a-f]+:[ 	]+66 b8 01 00 00 00[ 	]+mov[ 	]+\$0x1,%eax
+[ 	]*[0-9a-f]+:[ 	]+b8 02 00[ 	]+mov[ 	]+\$0x2,%ax
+[ 	]*[0-9a-f]+:[ 	]+66 b8 ff ff 00 00[ 	]+mov[ 	]+\$0xffff,%eax
+[ 	]*[0-9a-f]+:[ 	]+b8 fe ff[ 	]+mov[ 	]+\$0xfffe,%ax
+[ 	]*[0-9a-f]+:[ 	]+66 b8 01 00 00 00[ 	]+mov[ 	]+\$0x1,%eax
+[ 	]*[0-9a-f]+:[ 	]+b8 02 00[ 	]+mov[ 	]+\$0x2,%ax
+[ 	]*[0-9a-f]+:[ 	]+66 b8 ff ff ff ff[ 	]+mov[ 	]+\$0xffffffff,%eax
+[ 	]*[0-9a-f]+:[ 	]+b8 fe ff[ 	]+mov[ 	]+\$0xfffe,%ax
+[ 	]*[0-9a-f]+:[ 	]+66 8d 06 00 00[ 	]+lea[ 	]+0x0,%eax
+[ 	]*[0-9a-f]+:[ 	]+b8 00 00[ 	]+mov[ 	]+\$0x0,%ax
+[ 	]*[0-9a-f]+:[ 	]+66 b8 00 00 00 00[ 	]+mov[ 	]+\$0x0,%eax
+[ 	]*[0-9a-f]+:[ 	]+67 8d 05 00 00 00 00[ 	]+addr32 lea[ 	]+0x0,%ax
+[ 	]*[0-9a-f]+:[ 	]+66 b8 00 00 00 00[ 	]+mov[ 	]+\$0x0,%eax
+[ 	]*[0-9a-f]+:[ 	]+b8 00 00[ 	]+mov[ 	]+\$0x0,%ax
+[ 	]*[0-9a-f]+:[ 	]+8d 47 ff[ 	]+lea[ 	]+-0x1\(%bx\),%ax
+[ 	]*[0-9a-f]+:[ 	]+8d 87 01 00[ 	]+lea[ 	]+0x1\(%bx\),%ax
+#pass