[PATCH] aarch64: Fix typo in aarch64-ldp-fusion.cc:combine_reg_notes [PR114936]

[PATCH] aarch64: Fix typo in aarch64-ldp-fusion.cc:combine_reg_notes [PR114936]

[Alex Coplan]

[-- Attachment #1: Type: text/plain, Size: 1219 bytes --]

This fixes a typo in combine_reg_notes in the load/store pair fusion
pass.  As it stands, the calls to filter_notes store any
REG_FRAME_RELATED_EXPR to fr_expr with the following association:

 - i2 -> fr_expr[0]
 - i1 -> fr_expr[1]

but then the checks inside the following if statement expect the
opposite (more natural) association, i.e.:

 - i2 -> fr_expr[1]
 - i1 -> fr_expr[0]

this patch fixes the oversight by swapping the fr_expr indices in the
calls to filter_notes.

In hindsight it would probably have been less confusing / error-prone to
have combine_reg_notes take an array of two insns, then we wouldn't have
to mix 1-based and 0-based indexing as well as remembering to call
filter_notes in reverse program order.  This however is a minimal fix
for backporting purposes.

Many thanks to Matthew for spotting this typo and pointing it out to me.

Bootstrapped/regtested on aarch64-linux-gnu, OK for trunk and the 14
branch after the 14.1 release?

Thanks,
Alex

gcc/ChangeLog:

	PR target/114936
	* config/aarch64/aarch64-ldp-fusion.cc (combine_reg_notes):
	Ensure insn iN has its REG_FRAME_RELATED_EXPR (if any) stored in
	FR_EXPR[N-1], thus matching the correspondence expected by the
	copy_rtx calls.

[-- Attachment #2: patch.txt --]
[-- Type: text/plain, Size: 674 bytes --]

diff --git a/gcc/config/aarch64/aarch64-ldp-fusion.cc b/gcc/config/aarch64/aarch64-ldp-fusion.cc
index 0bc225dae7b..12ef305d8d3 100644
--- a/gcc/config/aarch64/aarch64-ldp-fusion.cc
+++ b/gcc/config/aarch64/aarch64-ldp-fusion.cc
@@ -1085,9 +1085,9 @@ combine_reg_notes (insn_info *i1, insn_info *i2, bool load_p)
   bool found_eh_region = false;
   rtx result = NULL_RTX;
   result = filter_notes (REG_NOTES (i2->rtl ()), result,
-			 &found_eh_region, fr_expr);
-  result = filter_notes (REG_NOTES (i1->rtl ()), result,
 			 &found_eh_region, fr_expr + 1);
+  result = filter_notes (REG_NOTES (i1->rtl ()), result,
+			 &found_eh_region, fr_expr);
 
   if (!load_p)
     {

Re: [PATCH] aarch64: Fix typo in aarch64-ldp-fusion.cc:combine_reg_notes [PR114936]

[Richard Earnshaw (lists)]

On 03/05/2024 15:45, Alex Coplan wrote:
> This fixes a typo in combine_reg_notes in the load/store pair fusion
> pass.  As it stands, the calls to filter_notes store any
> REG_FRAME_RELATED_EXPR to fr_expr with the following association:
> 
>  - i2 -> fr_expr[0]
>  - i1 -> fr_expr[1]
> 
> but then the checks inside the following if statement expect the
> opposite (more natural) association, i.e.:
> 
>  - i2 -> fr_expr[1]
>  - i1 -> fr_expr[0]
> 
> this patch fixes the oversight by swapping the fr_expr indices in the
> calls to filter_notes.
> 
> In hindsight it would probably have been less confusing / error-prone to
> have combine_reg_notes take an array of two insns, then we wouldn't have
> to mix 1-based and 0-based indexing as well as remembering to call
> filter_notes in reverse program order.  This however is a minimal fix
> for backporting purposes.
> 
> Many thanks to Matthew for spotting this typo and pointing it out to me.
> 
> Bootstrapped/regtested on aarch64-linux-gnu, OK for trunk and the 14
> branch after the 14.1 release?
> 
> Thanks,
> Alex
> 
> gcc/ChangeLog:
> 
> 	PR target/114936
> 	* config/aarch64/aarch64-ldp-fusion.cc (combine_reg_notes):
> 	Ensure insn iN has its REG_FRAME_RELATED_EXPR (if any) stored in
> 	FR_EXPR[N-1], thus matching the correspondence expected by the
> 	copy_rtx calls.


OK.

R.