RE: [PATCH 1/2, combine] Try REG_EQUAL for nonzero_bits

["Thomas Preud'homme" <thomas.preudhomme@arm.com>]

Hi,

first of all, sorry for the delay. We quickly entered stage 4 and I thought
it was best waiting for stage 1 to update you on this.

> From: gcc-patches-owner@gcc.gnu.org [mailto:gcc-patches-
> owner@gcc.gnu.org] On Behalf Of Thomas Preud'homme
> 
> Of course both approaches are not exclusive. I'll try to test with *both*
> rs6000 bootstrap and with a cross-compiler for one of these targets.

I did two experiments where I checked the impact of removing the code
guarded by SHORT_IMMEDIATES_SIGN_EXTEND. In the first one I removed
the code in both rtlanal.c and combine.c. In the second, I only removed the
code from combine.c (in both occurences). In both cases powerpc
bootstrap succeeded.

I then proceeded to use these 2 produced compilers to compile the same
gcc source (actually the source from removing all code guarded by the
macro). I compared the output of objdump on the resulting g++ and
found that in both case the output was different from the one without
any modification. Both diffs look like:

Disassembly of section .init:
@@ -1359,7 +1359,7 @@ Disassembly of section .text:
     10003a94:	f8 21 ff 81 	stdu    r1,-128(r1)
     10003a98:	eb e4 00 00 	ld      r31,0(r4)
     10003a9c:	3c 82 ff f8 	addis   r4,r2,-8
-    10003aa0:	38 84 d7 60 	addi    r4,r4,-10400
+    10003aa0:	38 84 d7 70 	addi    r4,r4,-10384
     10003aa4:	7f e3 fb 78 	mr      r3,r31
     10003aa8:	4b ff f0 d9 	bl      10002b80 <0000003d.plt_call.strcmp@@GLIBC_2.3+0>
     10003aac:	e8 41 00 28 	ld      r2,40(r1)
@@ -1371,7 +1371,7 @@ Disassembly of section .text:
     10003ac4:	79 2a ff e3 	rldicl. r10,r9,63,63
     10003ac8:	41 82 00 78 	beq-    10003b40 <._ZL22sanitize_spec_functioniPPKc+0xc0>
     10003acc:	3c 62 ff f8 	addis   r3,r2,-8
-    10003ad0:	38 63 f5 70 	addi    r3,r3,-2704
+    10003ad0:	38 63 f5 b0 	addi    r3,r3,-2640
     10003ad4:	38 21 00 80 	addi    r1,r1,128
     10003ad8:	e8 01 00 10 	ld      r0,16(r1)
     10003adc:	eb e1 ff f8 	ld      r31,-8(r1)

(this one is when comparing g++ compiled by GCC with partial removal of
the code guarded by the macro compared to compiled without GCC
being modified.

I may have done a mistake when doing the experiment though and can
do it again if you wish.

Best regards,

Thomas