[PATCH] xtensa: Fix 2 warnings during xtensa build [PR100841]

Jakub Jelinek jakub@redhat.com
Wed Jun 2 17:09:26 GMT 2021


Hi!

When building gcc targetting xtensa-linux, there are 2 warnings the PR
complains about:
../../gcc/dwarf2cfi.c: In function ‘void init_one_dwarf_reg_size(int, machine_mode, rtx, machine_mode, init_one_dwarf_reg_state*)’:
../../gcc/dwarf2cfi.c:291:12: warning: comparison of integer expressions of different signedness: ‘const unsigned int’ and ‘int’ [-Wsign-compare]
  291 |   if (rnum >= DWARF_FRAME_REGISTERS)
../../gcc/function.c: In function ‘void gen_call_used_regs_seq(rtx_insn*, unsigned int)’:
../../gcc/function.c:5897:63: warning: comparison of unsigned expression in ‘< 0’ is always false [-Wtype-limits]
 5897 |       if (crtl->uses_only_leaf_regs && LEAF_REG_REMAP (regno) < 0)
which might during bootstrap or when configured with --enable-werror-always
be turned into errors.

The first one is the -Wsign-compare warning, in c-family we do:
2281	      /* Do not warn if the signed quantity is an unsuffixed integer
2282		 literal (or some static constant expression involving such
2283		 literals or a conditional expression involving such literals)
2284		 and it is non-negative.  */
2285	      if (tree_expr_nonnegative_warnv_p (sop, &ovf))
2286		/* OK */;
and so don't warn if that function determines the expression is
non-negative.  But xtensa defines DWARF_FRAME_REGISTERS as
(16 + (something ? 0 : 1)) and that isn't handled by
tree_expr_nonnegative_warnv_p, VRP can handle it of course, but that is much
later.
The second chunk rewrites it into a form that tree_expr_nonnegative_warnv_p
can handle, in particular (something ? 16 : 16 + 1), where for COND_EXPRs
that function checks both the 2nd and 3rd operand of the ternary operator
and if both are nonnegative, returns true.

The other warning has been introduced fairly recently; LEAF_REG_REMAP is
currently used by 2 targets only, and is documented to yield -1 if a hard
reg number can't be remapped and the remapped register number otherwise.
That means that the type of the expression should be signed (otherwise -1
could never appear), and on SPARC indeed it is defined as
extern char leaf_reg_remap[];
#define LEAF_REG_REMAP(REGNO) (leaf_reg_remap[REGNO])
so unless the host is -funsigned-char by default it works fine.
I guess sparc.[ch] should be fixed to use signed char of leaf_reg_remap,
Eric?
The argument to LEAF_REG_REMAP is often unsigned int though, hard
register numbers are usually not negative, and thus the warning.
I think xtensa doesn't have 2G hard registers and so it is ok to just cast
it to int.

Verified just by making sure the warnings go away in a cross, ok for trunk?

2021-06-02  Jakub Jelinek  <jakub@redhat.com>

	PR target/100841
	* config/xtensa/xtensa.h (LEAF_REG_REMAP): Cast REGNO to int to avoid
	-Wtype-limits warnings.
	(DWARF_FRAME_REGISTER): Rewrite into ternary operator with addition
	in operands to avoid -Wsign-compare warnings.

--- gcc/config/xtensa/xtensa.h.jj	2021-01-04 10:25:45.570157539 +0100
+++ gcc/config/xtensa/xtensa.h	2021-06-02 17:41:04.190861829 +0200
@@ -279,7 +279,7 @@ extern const char xtensa_leaf_regs[FIRST
 
 /* For Xtensa, no remapping is necessary, but this macro must be
    defined if LEAF_REGISTERS is defined.  */
-#define LEAF_REG_REMAP(REGNO) (REGNO)
+#define LEAF_REG_REMAP(REGNO) ((int) (REGNO))
 
 /* This must be declared if LEAF_REGISTERS is set.  */
 extern int leaf_function;
@@ -775,8 +775,9 @@ typedef struct xtensa_args
 #define INCOMING_RETURN_ADDR_RTX gen_rtx_REG (Pmode, 0)
 #define DWARF_FRAME_RETURN_COLUMN DWARF_FRAME_REGNUM (0)
 #define DWARF_ALT_FRAME_RETURN_COLUMN 16
-#define DWARF_FRAME_REGISTERS (DWARF_ALT_FRAME_RETURN_COLUMN		\
-			       + (TARGET_WINDOWED_ABI ? 0 : 1))
+#define DWARF_FRAME_REGISTERS (TARGET_WINDOWED_ABI \
+			       ? DWARF_ALT_FRAME_RETURN_COLUMN		\
+			       : DWARF_ALT_FRAME_RETURN_COLUMN + 1)
 #define EH_RETURN_DATA_REGNO(N) ((N) < 2 ? (N) + 2 : INVALID_REGNUM)
 #define ASM_PREFERRED_EH_DATA_FORMAT(CODE, GLOBAL)			\
   (flag_pic								\

	Jakub



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