[Clang][X86] Replace F16C __builtin_ia32_vcvtph2ps/256 intrinsics with __builtin_convertvector

[RKSimon]

Similar to #152461, there doesn't appear to be any reason to have these when we can do the same with __builtin_shufflevector + __builtin_convertvector

This should also allow EmitX86CvtF16ToFloatExpr to be simplified as there will be fewer argument variants

Note this is just for PH2PS - not PS2PH which requires the rounding control immediate

[llvmbot]

Hi!

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[llvmbot]

@llvm/issue-subscribers-good-first-issue

Author: Simon Pilgrim (RKSimon)

Similar to #152461, there doesn't appear to be any reason to have these when we can do the same with __builtin_shufflevector + __builtin_convertvector

Note this is just for PH2PS - not PS2PH which requires the rounding control immediate

[llvmbot]

@llvm/issue-subscribers-backend-x86

Author: Simon Pilgrim (RKSimon)

Similar to #152461, there doesn't appear to be any reason to have these when we can do the same with __builtin_shufflevector + __builtin_convertvector

Note this is just for PH2PS - not PS2PH which requires the rounding control immediate

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Simon Pilgrim (RKSimon)

Similar to #152461, there doesn't appear to be any reason to have these when we can do the same with __builtin_shufflevector + __builtin_convertvector

Note this is just for PH2PS - not PS2PH which requires the rounding control immediate

[moorabbit]

Hi, can I be assigned this one as well?

[RKSimon]

We should be able to simplify the _cvtsh_ss helper as well to avoid it wrapping the __builtin_ia32_vcvtph2ps vector implementation