[llvm-bugs] [Bug 42876] New: bool != less efficient than bool ==

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=42876

            Bug ID: 42876
           Summary: bool != less efficient than bool ==
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Backend: RISC-V
          Assignee: unassignedbugs at nondot.org
          Reporter: efriedma at quicinc.com
                CC: llvm-bugs at lists.llvm.org, llvm-dev at redking.me.uk,
                    rofirrim at gmail.com

void a(_Bool a, _Bool b, void c()) { if (a==b) c(); }
void a2(_Bool a, _Bool b, void c()) { if (a!=b) c(); }

Build with clang -O2 --target=riscv32.  Output:

a:                                      # @a
# %bb.0:                                # %entry
        addi    sp, sp, -16
        sw      ra, 12(sp)
        bne     a0, a1, .LBB0_2

[...]

a2:                                     # @a2
# %bb.0:                                # %entry
        addi    sp, sp, -16
        sw      ra, 12(sp)
        xor     a0, a0, a1
        addi    a1, zero, 1
        bne     a0, a1, .LBB1_2

Something similar happens on some other targets; on x86 and 32-bit ARM, there's
an extra "cmp".

It looks like something weird is happening in target-independent SelectionDAG;
I haven't tried to dig further.

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