Re: [PATCH 0/2][IRA,LRA] Fix PR86939, IRA incorrectly creates an interference between a pseudo register and a hard register

[Peter Bergner <bergner@linux.ibm.com>]

On 10/2/18 9:59 AM, Peter Bergner wrote:
> gcc/
> 	PR rtl-optimization/86939
> 	PR rtl-optimization/87479
> 	* ira.h (copy_insn_p): New prototype.
> 	* ira-lives.c (ignore_reg_for_conflicts): New static variable.
> 	(make_hard_regno_dead): Don't add conflicts for register
> 	ignore_reg_for_conflicts.
> 	(make_object_dead): Likewise.
> 	(copy_insn_p): New function.
> 	(process_bb_node_lives): Set ignore_reg_for_conflicts for copies.
> 	Remove special conflict handling of REAL_PIC_OFFSET_TABLE_REGNUM.
> 	* lra-lives.c (ignore_reg_for_conflicts): New static variable.
> 	(make_hard_regno_dead): Don't add conflicts for register
> 	ignore_reg_for_conflicts.  Remove special conflict handling of
> 	REAL_PIC_OFFSET_TABLE_REGNUM.  Remove now unused argument
> 	check_pic_pseudo_p and update callers.
> 	(mark_pseudo_dead): Don't add conflicts for register
> 	ignore_reg_for_conflicts.
> 	(process_bb_lives): Set ignore_reg_for_conflicts for copies.

So bootstrap and regtesting on powerpc64le-linux show no regressions.
Looking at the x86_64-linux results, I see one test suite regression:

  FAIL: gcc.target/i386/pr49095.c scan-assembler-times \\), % 8

I have included the function that is compiled differently with and
without the patch.  Looking at the IRA rtl dumps, there is pseudo
85 that is copied from and into hard reg 5 and we now no longer
report that they conflict.  That allows pesudo 85 to now be assigned
to hard reg 5, rather than hard reg 3 (old code) and that leads
to the code differences shown below.  I don't know x86_64 mnemonics
enough to say whether the code changes below are "better" or "similar"
or ???.  H.J., can you comment on the below code gen changes?
If they're better or similar to the old code, I could just modify
the expected results for pr49095.c.

Peter



[bergner@dagger1 PR87479]$ cat pr49095.i 
void foo (void *);

int *
f1 (int *x)
{
  if (!--*x)
    foo (x);
  return x;
}
[bergner@dagger1 PR87479]$ /data/bergner/gcc/build/gcc-fsf-mainline-pr87479-base-regtest/gcc/xgcc -B/data/bergner/gcc/build/gcc-fsf-mainline-pr87479-base-regtest/gcc/ -Os -fno-shrink-wrap -masm=att -ffat-lto-objects -fno-ident -S -o pr49095-base.s pr49095.i 
[bergner@dagger1 PR87479]$ /data/bergner/gcc/build/gcc-fsf-mainline-pr87479-regtest/gcc/xgcc -B/data/bergner/gcc/build/gcc-fsf-mainline-pr87479-regtest/gcc/ -Os -fno-shrink-wrap -masm=att -ffat-lto-objects -fno-ident -S -o pr49095-new.s pr49095.i 
[bergner@dagger1 PR87479]$ diff -u pr49095-base.s pr49095-new.s 
--- pr49095-base.s	2018-10-02 14:07:09.000000000 -0500
+++ pr49095-new.s	2018-10-02 14:07:40.000000000 -0500
@@ -5,16 +5,16 @@
 f1:
 .LFB0:
 	.cfi_startproc
+	subq	$24, %rsp
+	.cfi_def_cfa_offset 32
 	decl	(%rdi)
-	pushq	%rbx
-	.cfi_def_cfa_offset 16
-	.cfi_offset 3, -16
-	movq	%rdi, %rbx
 	jne	.L2
+	movq	%rdi, 8(%rsp)
 	call	foo
+	movq	8(%rsp), %rdi
 .L2:
-	movq	%rbx, %rax
-	popq	%rbx
+	movq	%rdi, %rax
+	addq	$24, %rsp
 	.cfi_def_cfa_offset 8
 	ret
 	.cfi_endproc