[RFC PATCH] i386: Do not emit segment overrides for %p and %P [PR100936]

[Uros Bizjak via Gcc-patches]

Using %p to move the address of a symbol using LEA:

  asm ("lea %p1, %0" : "=r"(addr) : "m"(var));

emits assembler warning when VAR is declared in a non-generic address space:

  Warning: segment override on `lea' is ineffectual

The problem is with %p operand modifier, which should emit raw symbol name:

  p -- print raw symbol name.

Similar problem exists with %P modifier, trying to CALL or JMP to an
overridden symbol,e.g:

        call %gs:zzz
        jmp %gs:zzz

emits assembler warning:

  Warning: skipping prefixes on `call'
  Warning: skipping prefixes on `jmp'

Ensure that %p and %P never emit segment overrides.

2021-06-08  Uroš Bizjak  <ubiz...@gmail.com>

gcc/
    PR target/100936
    * config/i386/i386.c (print_operand_address_as): Rename "no_rip"
    argument to "raw".  Do not emit segment overrides when "raw" is true.

gcc/testsuite/

    PR target/100936
    * gcc.target/i386/pr100936.c: New test.

Bootstrapped and regression tested on x86_64-linux-gnu {,-m32}.

Uros.

diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
index b0d19a61a76..05b8dc806cd 100644
--- a/gcc/config/i386/i386.c
+++ b/gcc/config/i386/i386.c
@@ -13531,7 +13531,7 @@ ix86_print_operand_punct_valid_p (unsigned char code)
 
 static void
 ix86_print_operand_address_as (FILE *file, rtx addr,
-                              addr_space_t as, bool no_rip)
+                              addr_space_t as, bool raw)
 {
   struct ix86_address parts;
   rtx base, index, disp;
@@ -13570,7 +13570,7 @@ ix86_print_operand_address_as (FILE *file, rtx addr,
   else
     gcc_assert (ADDR_SPACE_GENERIC_P (parts.seg));
 
-  if (!ADDR_SPACE_GENERIC_P (as))
+  if (!ADDR_SPACE_GENERIC_P (as) && !raw)
     {
       if (ASSEMBLER_DIALECT == ASM_ATT)
        putc ('%', file);
@@ -13589,7 +13589,7 @@ ix86_print_operand_address_as (FILE *file, rtx addr,
     }
 
   /* Use one byte shorter RIP relative addressing for 64bit mode.  */
-  if (TARGET_64BIT && !base && !index && !no_rip)
+  if (TARGET_64BIT && !base && !index && !raw)
     {
       rtx symbol = disp;
 
diff --git a/gcc/testsuite/gcc.target/i386/pr100936.c 
b/gcc/testsuite/gcc.target/i386/pr100936.c
new file mode 100644
index 00000000000..c076cbb2405
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr100936.c
@@ -0,0 +1,34 @@
+/* PR target/100936 */
+/* { dg-do assemble } */
+/* { dg-options "-O2" } */
+
+__seg_gs int var;
+
+static int
+*foo (void)
+{
+  int *addr;
+
+  asm ("lea %p1, %0" : "=r"(addr) : "m"(var));
+
+  return addr;
+}
+
+static int
+bar (int *addr)
+{
+  int val;
+
+  asm ("mov %%gs:%1, %0" : "=r"(val) : "m"(*addr));
+
+  return val;
+}
+
+int
+baz (void)
+{
+  int *addr = foo();
+  int val = bar (addr);
+  
+  return val;
+}