[Bug target/115648] New: [15 Regression] GCN: [-PASS:-]{+FAIL:+} gcc.dg/hoist-register-pressure-{2, 3}.c scan-rtl-dump hoist "PRE/HOIST: end of bb .* copying expression"

[tschwinge at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115648

            Bug ID: 115648
           Summary: [15 Regression] GCN: [-PASS:-]{+FAIL:+}
                    gcc.dg/hoist-register-pressure-{2,3}.c scan-rtl-dump
                    hoist "PRE/HOIST: end of bb .* copying expression"
           Product: gcc
           Version: 15.0
            Status: UNCONFIRMED
          Keywords: testsuite-fail
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tschwinge at gcc dot gnu.org
                CC: ams at gcc dot gnu.org, guihaoc at gcc dot gnu.org
  Target Milestone: ---

Yesterday's commit r15-1575-gea8061f46a301797e7ba33b52e3b4713fb8e6b48 "fwprop:
invoke change_is_worthwhile to judge if a replacement is worthwhile" regresses
GCN target (tested '-march=gfx908'):

    PASS: gcc.dg/hoist-register-pressure-1.c (test for excess errors)
    PASS: gcc.dg/hoist-register-pressure-2.c (test for excess errors)
    [-PASS:-]{+FAIL:+} gcc.dg/hoist-register-pressure-2.c scan-rtl-dump hoist
"PRE/HOIST: end of bb .* copying expression"
    PASS: gcc.dg/hoist-register-pressure-3.c (test for excess errors)
    [-PASS:-]{+FAIL:+} gcc.dg/hoist-register-pressure-3.c scan-rtl-dump hoist
"PRE/HOIST: end of bb .* copying expression"

There is moderate code generation difference; I can't tell whether before vs.
after is better.  Does the compiler or the test cases or the compiler flags
need to be adjusted?  Re the latter, with '-fno-forward-propagate', we're back
to PASSing.