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[24.5.188.125]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-2bd9976e5absm401148a91.48.2024.05.21.08.15.57 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 21 May 2024 08:15:57 -0700 (PDT) Message-ID: <28aa12f4-3e44-4aa1-b51b-3fcef7f3e0e0@rivosinc.com> Date: Tue, 21 May 2024 08:15:56 -0700 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird From: Vineet Gupta Subject: Re: [PATCH v3 2/2] RISC-V: avoid LUI based const mat in alloca epilogue expansion To: Jeff Law , gcc-patches@gcc.gnu.org Cc: kito.cheng@gmail.com, Palmer Dabbelt , gnu-toolchain@rivosinc.com References: <20240520233237.109269-1-vineetg@rivosinc.com> <20240520233237.109269-2-vineetg@rivosinc.com> <5c0457b2-df23-49c4-9baa-a048cd2e56a5@gmail.com> Content-Language: en-US In-Reply-To: <5c0457b2-df23-49c4-9baa-a048cd2e56a5@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-4.8 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,RCVD_IN_DNSWL_NONE,SPF_HELO_NONE,SPF_PASS,TXREP autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: On 5/20/24 20:54, Jeff Law wrote: > On 5/20/24 5:32 PM, Vineet Gupta wrote: >> This is testsuite clean however there's a dwarf quirk which I want to >> run by the experts. The test that was tripping CI has following >> fragment: >> >> Before patch | After Patch >> ------------------------------------------------------ >> li t0,-4096 | addi sp,s0,-2048 >> addi t0,t0,560 | .cfi_def_cfa 2, 2048 <- #1 >> add sp,s0,t0 | addi sp,sp,-1488 >> .cfi_def_cfa 2, 3536 | .cfi_def_cfa_offset 3536 <- #2 >> addi sp,sp,1504 | addi sp,sp,1504 >> .cfi_def_cfa_offset 2032 | .cfi_def_cfa_offset 2032 <- #3 >> >> The dwarf insn #1 and #3 seem ok, however #2 seems dubious to me. > What about it seems dubious? My discomfort at claiming I understand dwarf, despite debugging/fixing the ARC Linux port's in kernel dwarf unwinder :-) > We need a CFA adjustment on each insn that > modifies the stack pointer so that we can unwind at any arbitrary point. Of course. > The first adjustment says the prior frame is at sp + 2048. Then it's at > sp + 3536. Then after the final insn the prior frame is at sp+2032. Yeah I got confused with second one since once it gets anchored to SP from S0, but you are right it is farther from base CFA now. -Vineet