This patch adds missing simplifications for (eq/ne (and/ior x C1) C2) in special cases. In the AND case, when (and C1 C2) is not equal to C1, some bits set in C2 are not set in C1, and thus (eq (and x C1) C2) can never be true. The OR case is similar when (and C1 C2) is not equal to C2.
The patch is meant to fix an ICE on RISC-V. In a former patch, I tried to change the insn condition directly, but Jeff pointed out that it was more reasonable to optimize it out before the split. As was suggested by Jeff, this patch tries to simplify the expression in simplify_relational_operation_1. The URL for the former patch: https://patchwork.sourceware.org/project/gcc/patch/[email protected]/ gcc/ChangeLog: * simplify-rtx.cc (simplify_context::simplify_relational_operation_1): Add simplifications for (eq/ne (and/ior x C1) C2) in special cases. gcc/testsuite/ChangeLog: * gcc.target/riscv/zbs-if_then_else-02.c: New test. --- gcc/simplify-rtx.cc | 30 +++++++++++++++++ .../gcc.target/riscv/zbs-if_then_else-02.c | 32 +++++++++++++++++++ 2 files changed, 62 insertions(+) create mode 100644 gcc/testsuite/gcc.target/riscv/zbs-if_then_else-02.c diff --git a/gcc/simplify-rtx.cc b/gcc/simplify-rtx.cc index 50fc51152ca..e2d5abf394f 100644 --- a/gcc/simplify-rtx.cc +++ b/gcc/simplify-rtx.cc @@ -6731,6 +6731,36 @@ simplify_context::simplify_relational_operation_1 (rtx_code code, } } + /* (eq/ne (and x C1) C2) simplifies to 0/1 if (and C1 C2) is not equal + to C1. Bits that are zero in C1 will be zero in the result, so if + C1 has any bits set that C2 doesn't have, the comparison can never + be true. */ + if ((code == EQ || code == NE) + && op0code == AND + && CONST_SCALAR_INT_P (op1) + && CONST_SCALAR_INT_P (XEXP (op0, 1))) + { + HOST_WIDE_INT c1 = INTVAL (XEXP (op0, 1)); + HOST_WIDE_INT c2 = INTVAL (op1); + if ((c1 & c2) != c1) + return code == EQ ? const0_rtx : const_true_rtx; + } + + /* (eq/ne (ior x C1) C2) simplifies to 0/1 if (and C1 C2) is not equal + to C2. Bits that are one in C1 will be one in the result, so if C2 + has any bits clear that C1 has set, the comparison can never be + true. */ + if ((code == EQ || code == NE) + && op0code == IOR + && CONST_SCALAR_INT_P (op1) + && CONST_SCALAR_INT_P (XEXP (op0, 1))) + { + HOST_WIDE_INT c1 = INTVAL (XEXP (op0, 1)); + HOST_WIDE_INT c2 = INTVAL (op1); + if ((c1 & c2) != c2) + return code == EQ ? const0_rtx : const_true_rtx; + } + /* (eq/ne (bswap x) C1) simplifies to (eq/ne x C2) with C2 swapped. */ if ((code == EQ || code == NE) && GET_CODE (op0) == BSWAP diff --git a/gcc/testsuite/gcc.target/riscv/zbs-if_then_else-02.c b/gcc/testsuite/gcc.target/riscv/zbs-if_then_else-02.c new file mode 100644 index 00000000000..3393bea8898 --- /dev/null +++ b/gcc/testsuite/gcc.target/riscv/zbs-if_then_else-02.c @@ -0,0 +1,32 @@ +/* { dg-do link { target { rv64 } } } */ +/* { dg-options "-march=rv64gc_zbb_zbs -mabi=lp64d -flto" } */ +/* { dg-skip-if "" { *-*-* } { "-O0" "-Og" "-O1" } } */ + +struct S { + int a; + char b; + int c; +} s; + +const signed char c = -37; +int d; +struct S v1[] = {{0, 8}, 0, 0, -108976}, v2[] = {{}, 0, 0, 2804}; +int a; +struct S v3[3]; +int *p = &a; + +void foo() { + int a; + if (a) + ; + else if (v1[0].b) + s.a = 0; + else + d = 0; + if (*p) + if (v3[1].c) + if (1 ^ (d & c & v2[1].c & ~v1[1].c | s.a)) + v3[2].c = 0; +} + +int main() { foo(); } -- 2.46.0
