[llvm-bugs] [Bug 50842] New: [X86] Failure to pull out common scaled index from address math

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=50842

            Bug ID: 50842
           Summary: [X86] Failure to pull out common scaled index from
                    address math
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Backend: X86
          Assignee: unassignedbugs at nondot.org
          Reporter: llvm-dev at redking.me.uk
                CC: craig.topper at gmail.com, llvm-bugs at lists.llvm.org,
                    llvm-dev at redking.me.uk, pengfei.wang at intel.com,
                    spatel+llvm at rotateright.com

https://c.godbolt.org/z/qd1EqKcdT

#include <stdint.h>
#include <stdio.h>

struct PayLoad {
    float *f32;
    double *f64;
    int32_t *i32;
    int64_t *i64;
};

size_t MoveEntry(PayLoad &data, size_t to, size_t N) {
    size_t from = N - 1;
    if (to < from) {
      data.f32[to] = data.f32[from];
      data.f64[to] = data.f64[from];
      data.i32[to] = data.i32[from];
      data.i64[to] = data.i64[from];
    }
    return N - 1;
}

The 'from' addresses all have a fixed offset from the %rdx scaled index that
could be removed if we used the %rax for the scaled index directly.

clang -g0 -O3

MoveEntry:
        leaq    -1(%rdx), %rax
        cmpq    %rsi, %rax
        jbe     .LBB0_2
        movq    (%rdi), %rcx
        movss   -4(%rcx,%rdx,4), %xmm0
        movss   %xmm0, (%rcx,%rsi,4)
        movq    8(%rdi), %rcx
        movsd   -8(%rcx,%rdx,8), %xmm0
        movsd   %xmm0, (%rcx,%rsi,8)
        movq    16(%rdi), %r8
        movl    -4(%r8,%rdx,4), %ecx
        movl    %ecx, (%r8,%rsi,4)
        movq    24(%rdi), %rcx
        movq    -8(%rcx,%rdx,8), %rdx
        movq    %rdx, (%rcx,%rsi,8)
.LBB0_2:
        retq


%struct.PayLoad = type { float*, double*, i32*, i64* }

define dso_local i64 @_Z9MoveEntryR7PayLoadmm(%struct.PayLoad* nocapture
nonnull readonly align 8 dereferenceable(32) %0, i64 %1, i64 %2)
local_unnamed_addr #0 {
  %4 = add i64 %2, -1
  %5 = icmp ugt i64 %4, %1
  br i1 %5, label %6, label %27

6:                                                ; preds = %3
  %7 = getelementptr inbounds %struct.PayLoad, %struct.PayLoad* %0, i64 0, i32
0
  %8 = load float*, float** %7, align 8, !tbaa !3
  %9 = getelementptr inbounds float, float* %8, i64 %4
  %10 = load float, float* %9, align 4, !tbaa !8
  %11 = getelementptr inbounds float, float* %8, i64 %1
  store float %10, float* %11, align 4, !tbaa !8
  %12 = getelementptr inbounds %struct.PayLoad, %struct.PayLoad* %0, i64 0, i32
1
  %13 = load double*, double** %12, align 8, !tbaa !10
  %14 = getelementptr inbounds double, double* %13, i64 %4
  %15 = load double, double* %14, align 8, !tbaa !11
  %16 = getelementptr inbounds double, double* %13, i64 %1
  store double %15, double* %16, align 8, !tbaa !11
  %17 = getelementptr inbounds %struct.PayLoad, %struct.PayLoad* %0, i64 0, i32
2
  %18 = load i32*, i32** %17, align 8, !tbaa !13
  %19 = getelementptr inbounds i32, i32* %18, i64 %4
  %20 = load i32, i32* %19, align 4, !tbaa !14
  %21 = getelementptr inbounds i32, i32* %18, i64 %1
  store i32 %20, i32* %21, align 4, !tbaa !14
  %22 = getelementptr inbounds %struct.PayLoad, %struct.PayLoad* %0, i64 0, i32
3
  %23 = load i64*, i64** %22, align 8, !tbaa !16
  %24 = getelementptr inbounds i64, i64* %23, i64 %4
  %25 = load i64, i64* %24, align 8, !tbaa !17
  %26 = getelementptr inbounds i64, i64* %23, i64 %1
  store i64 %25, i64* %26, align 8, !tbaa !17
  br label %27

27:                                               ; preds = %6, %3
  ret i64 %4
}

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