[llvm-bugs] [Bug 43745] New: [SLP] Failure to create v2f64 comparison reductions

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=43745

            Bug ID: 43745
           Summary: [SLP] Failure to create v2f64 comparison reductions
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Scalar Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: llvm-dev at redking.me.uk
                CC: a.bataev at hotmail.com, andrea.dibiagio at gmail.com,
                    craig.topper at gmail.com, llvm-bugs at lists.llvm.org,
                    spatel+llvm at rotateright.com

Current Codegen: https://godbolt.org/z/n0UB_k

Pulled out of the c-ray benchmark:

#define ERR_MARGIN 1e-6

bool cmp_lt_gt(double a, double b, double c) {
  double t1 = (-b + c) / (2.0 * a);
  double t2 = (-b - c) / (2.0 * a);

  if((t1 < ERR_MARGIN && t2 < ERR_MARGIN) || (t1 > 1.0 && t2 > 1.0))
    return 0;
  return 1;
}

SLP fails to create AND reductions for either of these, let alone merge them
into a single (tweaked) reduction (and branch). Oddly it also manages to
vectorize only one of the comparisons but then fails to form a reduction for
the result.

clang -g0 -O3 -march=btver2 -emit-llvm

define i1 @_Z9cmp_lt_gtddd(double %0, double %1, double %2) {
  %4 = fneg double %1
  %5 = fmul double %0, 2.000000e+00
  %6 = insertelement <2 x double> undef, double %4, i32 0
  %7 = insertelement <2 x double> %6, double %2, i32 1
  %8 = insertelement <2 x double> undef, double %2, i32 0
  %9 = insertelement <2 x double> %8, double %1, i32 1
  %10 = fsub <2 x double> %7, %9
  %11 = insertelement <2 x double> undef, double %5, i32 0
  %12 = shufflevector <2 x double> %11, <2 x double> undef, <2 x i32>
zeroinitializer
  %13 = fdiv <2 x double> %10, %12
  %14 = extractelement <2 x double> %13, i32 1
  %15 = fcmp olt double %14, 0x3EB0C6F7A0B5ED8D
  %16 = extractelement <2 x double> %13, i32 0
  %17 = fcmp olt double %16, 0x3EB0C6F7A0B5ED8D
  %18 = and i1 %15, %17
  br i1 %18, label %24, label %19

19: ; preds = %3
  %20 = fcmp ule <2 x double> %13, <double 1.000000e+00, double 1.000000e+00>
  %21 = extractelement <2 x i1> %20, i32 0
  %22 = extractelement <2 x i1> %20, i32 1
  %23 = or i1 %21, %22
  ret i1 %23

24: ; preds = %3
  ret i1 false
}

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