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- From b62c6d08720ed3c4dafef314816e09d8769b373a Mon Sep 17 00:00:00 2001
- From: Vineet Gupta <vineetg@rivosinc.com>
- Date: Tue, 5 Sep 2023 07:55:07 -0700
- Subject: [PATCH 15/30] 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>
- ---
- 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 4619220ef8a..1721e1011ea 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
- --
- 2.25.1
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