I sometimes find myself scouring assembler output from the compiler
and trying to figure out which instructions correspond to which
lines of source code; I believe this is a common activity for some
end-users.
The following patch adds a new -fasm-show-source option, which
emits comments into the generated asm showing the pertinent
line of source code, whenever it changes. It uses the same logic
as debug_hooks->source_line for tracking this (for handling
line-based breakpoints).
An example can be seen in the invoke.texi part of the patch. As
noted there, it's aimed at end-users, rather than gcc developers.
The example shows a relatively short function; the option is
likely to be much more useful for longer functions.
I think it would further improve usability if this option were enabled
by default when the final output is .s (either via -S, or by "-o foo.s").
Ideas on how to implement that (in the driver) would be welcome - I
started looking at the spec-handling code, but thought I'd post the
idea here first, before diving in too deeply.
Successfully bootstrapped®rtested on x86_64-pc-linux-gnu; adds
2 PASS results to gcc.sum.
Thoughts? OK for trunk as-is?
gcc/ChangeLog:
* common.opt (fasm-show-source): New option.
* doc/invoke.texi (Code Generation Options): Add
-fasm-show-source.
(-fasm-show-source): New item.
* final.c (asm_show_source): New function.
(final_scan_insn): Call asm_show_source.
gcc/testsuite/ChangeLog:
* gcc.dg/fasm-show-source-1.c: New test case.
---
gcc/common.opt | 5 +++
gcc/doc/invoke.texi | 71 ++++++++++++++++++++++++++++++-
gcc/final.c | 29 ++++++++++++-
gcc/testsuite/gcc.dg/fasm-show-source-1.c | 15 +++++++
4 files changed, 117 insertions(+), 3 deletions(-)
create mode 100644 gcc/testsuite/gcc.dg/fasm-show-source-1.c
diff --git a/gcc/common.opt b/gcc/common.opt
index 8a292ed..56ce513 100644
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -939,6 +939,11 @@ fargument-noalias-anything
Common Ignore
Does nothing. Preserved for backward compatibility.
+fasm-show-source
+Common Var(flag_asm_show_source)
+Emit comments in the generated assembly code to show the source code
+lines associated with the assembly instructions.
+
fsanitize=
Common Driver Report Joined
Select what to sanitize.
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 22001f9..dc3d3ad 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -486,7 +486,8 @@ Objective-C and Objective-C++ Dialects}.
@item Code Generation Options
@xref{Code Gen Options,,Options for Code Generation Conventions}.
-@gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol
+@gccoptlist{-fasm-show-source @gol
+-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol
-ffixed-@var{reg} -fexceptions @gol
-fnon-call-exceptions -fdelete-dead-exceptions -funwind-tables @gol
-fasynchronous-unwind-tables @gol
@@ -11153,6 +11154,74 @@ can figure out the other form by either removing
@samp{no-} or adding
it.
@table @gcctabopt
+@item -fasm-show-source
+@opindex fasm-show-source
+Emit comments in the generated assembly code to show the source code
+lines associated with the assembly instructions. This option is
+aimed at end-users who wish to better understand the relationship
+between their source code and the generated machine code.
+
+The comments are of the form FILENAME:LINENUMBER:CONTENT OF LINE.
+
+For example, given this C source file:
+
+@smallexample
+int test (int n)
+@{
+ int i;
+ int total = 0;
+
+ for (i = 0; i < n; i++)
+ total += i * i;
+
+ return total;
+@}
+@end smallexample
+
+compiling to (x86_64) assembly via @option{-S} and emitting the result
+direct to stdout via @option{-o} @option{-}
+
+@smallexample
+gcc -S test.c -fasm-show-source -Os -o -
+@end smallexample
+
+gives output similar to this, highlighting which instructions correspond
+to the various parts of the loop:
+
+@smallexample
+ .file "test.c"
+ .text
+ .globl test
+ .type test, @@function
+test:
+.LFB0:
+ .cfi_startproc
+# test.c:4: int total = 0;
+ xorl %eax, %eax
+# test.c:6: for (i = 0; i < n; i++)
+ xorl %edx, %edx
+.L2:
+# test.c:6: for (i = 0; i < n; i++)
+ cmpl %edi, %edx
+ jge .L5
+# test.c:7: total += i * i;
+ movl %edx, %ecx
+ imull %edx, %ecx
+# test.c:6: for (i = 0; i < n; i++)
+ incl %edx
+# test.c:7: total += i * i;
+ addl %ecx, %eax
+ jmp .L2
+.L5:
+# test.c:10: @}
+ ret
+ .cfi_endproc
+.LFE0:
+ .size test, .-test
+ .ident "GCC: (GNU) 7.0.0 20160809 (experimental)"
+ .section .note.GNU-stack,"",@@progbits
+@end smallexample
+
@item -fstack-reuse=@var{reuse-level}
@opindex fstack_reuse
This option controls stack space reuse for user declared local/auto variables
diff --git a/gcc/final.c b/gcc/final.c
index 5b04311..09bf0b7 100644
--- a/gcc/final.c
+++ b/gcc/final.c
@@ -2140,6 +2140,27 @@ call_from_call_insn (rtx_call_insn *insn)
return x;
}
+/* Implementation of -fasm-show-source.
+ Print a comment into the asm showing FILENAME, LINENUM, and the
+ corresponding source line, if available. */
+
+static void
+asm_show_source (const char *filename, int linenum)
+{
+ if (!filename)
+ return;
+
+ int line_size;
+ const char *line = location_get_source_line (filename, linenum, &line_size);
+ if (!line)
+ return;
+
+ fprintf (asm_out_file, "%s %s:%i: ", ASM_COMMENT_START, filename, linenum);
+ /* "line" is not 0-terminated, so we must use line_size. */
+ fwrite (line, 1, line_size, asm_out_file);
+ fputc ('\n', asm_out_file);
+}
+
/* The final scan for one insn, INSN.
Args are same as in `final', except that INSN
is the insn being scanned.
@@ -2563,8 +2584,12 @@ final_scan_insn (rtx_insn *insn, FILE *file, int
optimize_p ATTRIBUTE_UNUSED,
note in a row. */
if (!DECL_IGNORED_P (current_function_decl)
&& notice_source_line (insn, &is_stmt))
- (*debug_hooks->source_line) (last_linenum, last_filename,
- last_discriminator, is_stmt);
+ {
+ if (flag_asm_show_source)
+ asm_show_source (last_filename, last_linenum);
+ (*debug_hooks->source_line) (last_linenum, last_filename,
+ last_discriminator, is_stmt);
+ }
if (GET_CODE (body) == PARALLEL
&& GET_CODE (XVECEXP (body, 0, 0)) == ASM_INPUT)
diff --git a/gcc/testsuite/gcc.dg/fasm-show-source-1.c
b/gcc/testsuite/gcc.dg/fasm-show-source-1.c
new file mode 100644
index 0000000..3dd49e0
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/fasm-show-source-1.c
@@ -0,0 +1,15 @@
+/* Ensure that the generated asm contains FIXME */
+/* { dg-options "-fasm-show-source" } */
+
+int test (int n)
+{
+ int i;
+ int total = 0;
+
+ for (i = 0; i < n; i++)
+ total += i * i;
+
+ return total;
+}
+
+/* { dg-final { scan-assembler "total = 0" } } */
--
1.8.5.3
