https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105137
--- Comment #2 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Roger Sayle <sa...@gcc.gnu.org>: https://gcc.gnu.org/g:4f1314f547f69d3a2b1f16ce301267e3bfb4e427 commit r13-4945-g4f1314f547f69d3a2b1f16ce301267e3bfb4e427 Author: Roger Sayle <ro...@nextmovesoftware.com> Date: Sun Jan 1 17:00:28 2023 +0000 Add post-reload splitter for extendditi2 on x86_64. This is another step towards a possible solution for PR 105137. This patch introduces a define_insn for extendditi2 that allows DImode to TImode sign-extension to be represented in the early RTL optimizers, before being split post-reload into the exact same idiom as currently produced by RTL expansion. Typically this produces the identical code, so the first new test case: __int128 foo(long long x) { return (__int128)x; } continues to generate: foo: movq %rdi, %rax cqto ret The "magic" is that this representation allows combine and the other RTL optimizers to do a better job. Hence, the second test case: __int128 foo(__int128 a, long long b) { a += ((__int128)b) << 70; return a; } which mainline with -O2 currently generates as: foo: movq %rsi, %rax movq %rdx, %rcx movq %rdi, %rsi salq $6, %rcx movq %rax, %rdi xorl %eax, %eax movq %rcx, %rdx addq %rsi, %rax adcq %rdi, %rdx ret with this patch now becomes: foo: movl $0, %eax salq $6, %rdx addq %rdi, %rax adcq %rsi, %rdx ret i.e. the same code for the signed and unsigned extension variants. 2023-01-01 Roger Sayle <ro...@nextmovesoftware.com> Uroš Bizjak <ubiz...@gmail.com> gcc/ChangeLog * config/i386/i386.md (extendditi2): New define_insn. (define_split): Use DWIH mode iterator to treat new extendditi2 identically to existing extendsidi2_1. (define_peephole2): Likewise. (define_peephole2): Likewise. (define_Split): Likewise. gcc/testsuite/ChangeLog * gcc.target/i386/extendditi2-1.c: New test case. * gcc.target/i386/extendditi2-2.c: Likewise.
