x86: PR target/103773: Fix wrong-code with -Oz from pop to memory.

This is a fix to PR target/103773 where -Oz shouldn't use push/pop
on x86 to shrink writing small integer constants to memory.
Instead clang uses "andl $0, mem" for writing zero, and "orl $-1, mem"
when writing -1 to memory when using -Oz.  This patch implements this
via peephole2 where we can confirm that its ok to clobber the flags.

2021-12-23  Roger Sayle  <roger@nextmovesoftware.com>
	    Uroš Bizjak  <ubizjak@gmail.com>

gcc/ChangeLog
	PR target/103773
	* config/i386/i386.md (*mov<mode>_and): New define_insn for
	writing a zero to memory using AND.
	(*mov<mode>_or): Extend to allow memory destination and HImode.
	(*movdi_internal): Remove -Oz push/pop optimization from here.
	(*movsi_internal): Likewise.
	(peephole2): Perform -Oz push/pop optimization here, only for
	register destinations, values other than zero, and in functions
	that don't used the red zone.
	(peephole2): With -Oz, convert writes of 0 or -1 to memory into
	their clobber forms, i.e. *mov<mode>_and and *mov<mode>_or resp.

gcc/testsuite/ChangeLog
	PR target/103773
	* gcc.target/i386/pr103773-2.c: New test case.
	* gcc.target/i386/pr103773.c: New test case.

diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
index 58b1064..284b950 100644 (file)
--- a/gcc/config/i386/i386.md
+++ b/gcc/config/i386/i386.md
@@ -2028,9 +2028,19 @@
    (set_attr "mode" "SI")
    (set_attr "length_immediate" "0")])
 
+(define_insn "*mov<mode>_and"
+  [(set (match_operand:SWI248 0 "memory_operand" "=m")
+       (match_operand:SWI248 1 "const0_operand"))
+   (clobber (reg:CC FLAGS_REG))]
+  "reload_completed"
+  "and{<imodesuffix>}\t{%1, %0|%0, %1}"
+  [(set_attr "type" "alu1")
+   (set_attr "mode" "<MODE>")
+   (set_attr "length_immediate" "1")])
+
 (define_insn "*mov<mode>_or"
-  [(set (match_operand:SWI48 0 "register_operand" "=r")
-       (match_operand:SWI48 1 "constm1_operand"))
+  [(set (match_operand:SWI248 0 "nonimmediate_operand" "=rm")
+       (match_operand:SWI248 1 "constm1_operand"))
    (clobber (reg:CC FLAGS_REG))]
   "reload_completed"
   "or{<imodesuffix>}\t{%1, %0|%0, %1}"
@@ -2218,14 +2228,7 @@
     case TYPE_IMOV:
       gcc_assert (!flag_pic || LEGITIMATE_PIC_OPERAND_P (operands[1]));
       if (get_attr_mode (insn) == MODE_SI)
-       {
-         if (optimize_size > 1
-             && TARGET_64BIT
-             && CONST_INT_P (operands[1])
-             && IN_RANGE (INTVAL (operands[1]), -128, 127))
-           return "push{q}\t%1\n\tpop{q}\t%0";
-         return "mov{l}\t{%k1, %k0|%k0, %k1}";
-       }
+       return "mov{l}\t{%k1, %k0|%k0, %k1}";
       else if (which_alternative == 4)
        return "movabs{q}\t{%1, %0|%0, %1}";
       else if (ix86_use_lea_for_mov (insn, operands))
@@ -2443,14 +2446,6 @@
       gcc_assert (!flag_pic || LEGITIMATE_PIC_OPERAND_P (operands[1]));
       if (ix86_use_lea_for_mov (insn, operands))
        return "lea{l}\t{%E1, %0|%0, %E1}";
-      else if (optimize_size > 1
-              && CONST_INT_P (operands[1])
-              && IN_RANGE (INTVAL (operands[1]), -128, 127))
-       {
-         if (TARGET_64BIT)
-           return "push{q}\t%1\n\tpop{q}\t%q0";
-         return "push{l}\t%1\n\tpop{l}\t%0";
-       }
       else
        return "mov{l}\t{%1, %0|%0, %1}";
 
@@ -2514,6 +2509,37 @@
           ]
           (symbol_ref "true")))])
 
+;; With -Oz, transform mov $imm,reg to the shorter push $imm; pop reg.
+(define_peephole2
+  [(set (match_operand:SWI248 0 "general_reg_operand")
+       (match_operand:SWI248 1 "const_int_operand"))]
+  "optimize_insn_for_size_p () && optimize_size > 1
+   && operands[1] != const0_rtx
+   && IN_RANGE (INTVAL (operands[1]), -128, 127)
+   && !ix86_red_zone_used"
+  [(set (match_dup 2) (match_dup 1))
+   (set (match_dup 0) (match_dup 3))]
+{
+  if (GET_MODE (operands[0]) != word_mode)
+    operands[0] = gen_rtx_REG (word_mode, REGNO (operands[0]));
+
+  operands[2] = gen_rtx_MEM (word_mode,
+                            gen_rtx_PRE_DEC (Pmode, stack_pointer_rtx));
+  operands[3] = gen_rtx_MEM (word_mode,
+                            gen_rtx_POST_INC (Pmode, stack_pointer_rtx));
+})
+
+;; With -Oz, transform mov $0,mem to the shorter and $0,mem.
+;; Likewise, transform mov $-1,mem to the shorter or $-1,mem.
+(define_peephole2
+  [(set (match_operand:SWI248 0 "memory_operand")
+       (match_operand:SWI248 1 "const_int_operand"))]
+  "(operands[1] == const0_rtx || operands[1] == constm1_rtx)
+   && optimize_insn_for_size_p () && optimize_size > 1
+   && peep2_regno_dead_p (0, FLAGS_REG)"
+  [(parallel [(set (match_dup 0) (match_dup 1))
+              (clobber (reg:CC FLAGS_REG))])])
+
 (define_insn "*movhi_internal"
   [(set (match_operand:HI 0 "nonimmediate_operand"
     "=r,r,r,m ,*k,*k ,r ,m ,*k ,?r,?*v,*v,*v,*v,m")

diff --git a/gcc/testsuite/gcc.target/i386/pr103773-2.c b/gcc/testsuite/gcc.target/i386/pr103773-2.c
new file mode 100644 (file)
index 0000000..9dafebd
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr103773-2.c
@@ -0,0 +1,19 @@
+/* { dg-do compile } */
+/* { dg-options "-Oz" } */
+short s;
+int i;
+long long l;
+
+void s0() { s = 0; }
+void sm1() { s = -1; }
+void i0() { i = 0; }
+void im1() { i = -1; }
+void l0() { l = 0; }
+void lm1() { l = -1; }
+
+/* { dg-final { scan-assembler-not "\tmov\[wlq\]\t\\\$0," } } */
+/* { dg-final { scan-assembler-not "\tmov\[wlq\]\t\\\$-1," } } */
+/* { dg-final { scan-assembler "\tandw\t\\\$0," } } */
+/* { dg-final { scan-assembler "\torw\t\\\$-1," } } */
+/* { dg-final { scan-assembler "\torl\t\\\$-1," } } */
+

diff --git a/gcc/testsuite/gcc.target/i386/pr103773.c b/gcc/testsuite/gcc.target/i386/pr103773.c
new file mode 100644 (file)
index 0000000..1e4b8ce
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr103773.c
@@ -0,0 +1,12 @@
+/* { dg-do run } */
+/* { dg-options "-Oz" } */
+
+unsigned long long x;
+
+int main (void)
+{
+  __builtin_memset (&x, 0xff, 4);
+  if (x != 0xffffffff)
+    __builtin_abort ();
+  return 0;
+}