[llvm-bugs] [Bug 37798] New: [X86] Add support for X86ISD float2int constant folding

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=37798

            Bug ID: 37798
           Summary: [X86] Add support for X86ISD float2int constant
                    folding
           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: andrea.dibiagio at gmail.com, craig.topper at gmail.com,
                    filcab at gmail.com, greg.bedwell at sony.com,
                    lebedev.ri at gmail.com, llvm-bugs at lists.llvm.org,
                    spatel+llvm at rotateright.com
        Depends on: 37751

Split off from [Bug #37751].

Now that we've standardised to using X86ISD opcodes for float2int conversions:

      // Vector float/double to signed/unsigned integer.
      CVTP2SI, CVTP2UI, CVTP2SI_RND, CVTP2UI_RND,
      // Scalar float/double to signed/unsigned integer.
      CVTS2SI_RND, CVTS2UI_RND,

      // Vector float/double to signed/unsigned integer with truncation.
      CVTTP2SI, CVTTP2UI, CVTTP2SI_RND, CVTTP2UI_RND,
      // Scalar float/double to signed/unsigned integer with truncation.
      CVTTS2SI_RND, CVTTS2UI_RND,

We should investigate adding safe constant folding support to these. We could
at least support exact conversions (these should be rounding mode independent
for non-truncation instructions?).

For truncation instructions we can probably accept inexact conversions as well,
as long as no underflow/overflow occurs - this would need to be tested to
confirm.


Referenced Bugs:

https://bugs.llvm.org/show_bug.cgi?id=37751
[Bug 37751] [X86] CVTTPD2DQ/CVTTPS2DQ intrinsics must not map to
ISD::FP_TO_SINT etc.
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