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Since PR37922 fix RTL DSE has hard register conflict checking in replace_read, so that if the replacement sequence sets (or typically just clobbers) some hard register (usually condition codes) we verify that hard register is not live. Unfortunately, it compares the hard reg set clobbered/set by the sequence (regs_set) against the currently live hard register set, but it then emits the insn sequence not at the current insn position, but before store_insn->insn. So, we should not compare against the current live hard register set, but against the hard register live set at the point of the store insn. Fortunately, we already have that remembered in store_insn->fixed_regs_live. In addition to bootstrapping/regtesting this patch on x86_64-linux and i686-linux, I've also added statistics gathering and it seems the only place where we end up rejecting the replace_read is the newly added testcase (the PR37922 is no longer effective at that) and fixed_regs_live has been always non-NULL at the if (store_insn->fixed_regs_live) spot. Rather than having there an assert, I chose to just keep regs_set as is, which means in that hypothetical case where fixed_regs_live wouldn't be computed for some store we'd still accept sequences that don't clobber/set any hard registers and just punt on those that clobber/set those. 2021-04-03 Jakub Jelinek <jakub@redhat.com> PR rtl-optimization/99863 * dse.c (replace_read): Drop regs_live argument. Instead of regs_live, use store_insn->fixed_regs_live if non-NULL, otherwise punt if insns sequence clobbers or sets any hard registers. * gcc.target/i386/pr99863.c: New test.
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