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From: Jeff Law <law@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org Subject: [gcc(refs/vendors/riscv/heads/gcc-13-with-riscv-opts)] RISC-V: zicond: Fix opt2 pattern Date: Mon, 11 Sep 2023 13:36:38 +0000 (GMT) [thread overview] Message-ID: <20230911133638.73C3E3857345@sourceware.org> (raw) https://gcc.gnu.org/g:cbd9bae2948918f04d4bfdcd1f2052ad4b43fc06 commit cbd9bae2948918f04d4bfdcd1f2052ad4b43fc06 Author: Vineet Gupta <vineetg@rivosinc.com> Date: Tue Sep 5 07:55:07 2023 -0700 RISC-V: zicond: Fix opt2 pattern Fixes: 1d5bc3285e8a ("[committed][RISC-V] Fix 20010221-1.c with zicond") This was tripping up gcc.c-torture/execute/pr60003.c at -O1 since in failing case, pattern semantics were not matching with asm czero.nez We start with the following src code snippet: if (a == 0) return 0; else return x; } which is equivalent to: "x = (a != 0) ? x : a" where x is NOT 0. ^^^^^^^^^^^^^^^^ and matches define_insn "*czero.nez.<GPR:mode><X:mode>.opt2" | (insn 41 20 38 3 (set (reg/v:DI 136 [ x ]) | (if_then_else:DI (ne (reg/v:DI 134 [ a ]) | (const_int 0 [0])) | (reg/v:DI 136 [ x ]) | (reg/v:DI 134 [ a ]))) {*czero.nez.didi.opt2} The corresponding asm pattern generates czero.nez x, x, a ; %0, %2, %1 which implies "x = (a != 0) ? 0 : a" clearly not what the pattern wants to do. Essentially "(a != 0) ? x : a" cannot be expressed with CZERO.nez if X is not guaranteed to be 0. However this can be fixed with a small tweak "x = (a != 0) ? x : a" is same as "x = (a == 0) ? a : x" and since middle operand is 0 when a == 0, it is equivalent to "x = (a == 0) ? 0 : x" which can be expressed with CZERO.eqz before fix after fix ----------------- ----------------- li a5,1 li a5,1 ld a4,8(sp) ld a4,8(sp) czero.nez a0,a4,a5 czero.eqz a0,a4,a5 The issue only happens at -O1 as at higher optimization levels, the whole conditional move gets optimized away. This fixes 4 testsuite failues in a zicond build: FAIL: gcc.c-torture/execute/pr60003.c -O1 execution test FAIL: gcc.dg/setjmp-3.c execution test FAIL: gcc.dg/torture/stackalign/setjmp-3.c -O1 execution test FAIL: gcc.dg/torture/stackalign/setjmp-3.c -O1 -fpic execution test gcc/ChangeLog: * config/riscv/zicond.md: Fix op2 pattern. Signed-off-by: Vineet Gupta <vineetg@rivosinc.com> (cherry picked from commit e87212ead5e9f36945b5e2d290187e2adca34da5) Diff: --- gcc/config/riscv/zicond.md | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/gcc/config/riscv/zicond.md b/gcc/config/riscv/zicond.md index 4619220ef8ac..1721e1011ea8 100644 --- a/gcc/config/riscv/zicond.md +++ b/gcc/config/riscv/zicond.md @@ -60,7 +60,7 @@ (match_operand:GPR 2 "register_operand" "r") (match_operand:GPR 3 "register_operand" "1")))] "TARGET_ZICOND && rtx_equal_p (operands[1], operands[3])" - "czero.nez\t%0,%2,%1" + "czero.eqz\t%0,%2,%1" ) ;; Combine creates this form in some cases (particularly the coremark
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