[llvm-bugs] [Bug 26701] New: [x86, SSE] missing optimizations for pos/neg integer vector comparisons

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=26701

            Bug ID: 26701
           Summary: [x86, SSE] missing optimizations for pos/neg integer
                    vector comparisons
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Backend: X86
          Assignee: unassignedbugs at nondot.org
          Reporter: spatel+llvm at rotateright.com
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

Checking if integer vector elements are positive or negative would seem to be a
common operation, but we don't handle this very well. We need to do extra work
because SSE/AVX only provide 2 integer comparison instructions (eq/gt):

define <4 x i32> @is_positive_using_signshift(<4 x i32> %x) {
  %sign = ashr <4 x i32> %x, <i32 31, i32 31, i32 31, i32 31>
  %not = xor <4 x i32> %sign, <i32 -1, i32 -1, i32 -1, i32 -1>
  ret <4 x i32> %not
}

define <4 x i32> @is_positive_using_sge(<4 x i32> %x) {
  %cmp = icmp sge <4 x i32> %x, zeroinitializer
  %sext = sext <4 x i1> %cmp to <4 x i32>
  ret <4 x i32> %sext
}

define <4 x i32> @is_positive_using_sgt(<4 x i32> %x) {
  %cmp = icmp sgt <4 x i32> %x, <i32 -1, i32 -1, i32 -1, i32 -1>
  %sext = sext <4 x i1> %cmp to <4 x i32>
  ret <4 x i32> %sext
}

define <4 x i32> @is_negative_using_signshift(<4 x i32> %x) {
  %sign = ashr <4 x i32> %x, <i32 31, i32 31, i32 31, i32 31>
  ret <4 x i32> %sign
}

define <4 x i32> @is_negative_using_slt(<4 x i32> %x) {
  %cmp = icmp slt <4 x i32> %x, zeroinitializer
  %sext = sext <4 x i1> %cmp to <4 x i32>
  ret <4 x i32> %sext
}

define <4 x i32> @is_negative_using_sle(<4 x i32> %x) {
  %cmp = icmp sle <4 x i32> %x, <i32 -1, i32 -1, i32 -1, i32 -1>
  %sext = sext <4 x i1> %cmp to <4 x i32>
  ret <4 x i32> %sext
}

$ ./llc -o - pcmp.ll -mattr=avx
_is_positive_using_signshift: 
    vpsrad    $31, %xmm0, %xmm0
    vpcmpeqd    %xmm1, %xmm1, %xmm1
    vpxor    %xmm1, %xmm0, %xmm0
    retq

_is_positive_using_sge:   
    vpxor    %xmm1, %xmm1, %xmm1
    vpcmpgtd    %xmm0, %xmm1, %xmm0
    vpcmpeqd    %xmm1, %xmm1, %xmm1
    vpxor    %xmm1, %xmm0, %xmm0
    retq

_is_positive_using_sgt:  
    vpcmpeqd    %xmm1, %xmm1, %xmm1
    vpcmpgtd    %xmm1, %xmm0, %xmm0
    retq

_is_negative_using_signshift: 
    vpsrad    $31, %xmm0, %xmm0
    retq

_is_negative_using_slt:         
    vpxor    %xmm1, %xmm1, %xmm1
    vpcmpgtd    %xmm0, %xmm1, %xmm0
    retq

_is_negative_using_sle:           
    vpcmpeqd    %xmm1, %xmm1, %xmm1
    vpcmpgtd    %xmm1, %xmm0, %xmm0
    vpxor    %xmm1, %xmm0, %xmm0
    retq

-- 
You are receiving this mail because:
You are on the CC list for the bug.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-bugs/attachments/20160222/8c6a6170/attachment.html>