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Re: [Patch AArch64] Add floatdihf2 and floatunsdihf2 patterns



On 06/09/16 10:19, James Greenhalgh wrote:
Hi,

This patch adds patterns for conversion from 64-bit integer to 16-bit
floating-point values under AArch64 targets which don't have support for
the ARMv8.2-A 16-bit floating point extensions.

We implement these by first saturating to a SImode (we know that any
values >= 65504 will round to infinity after conversion to HFmode), then
converting to a DFmode (unsigned conversions could go to SFmode, but there
is no performance benefit to this). Then converting to HFmode.

Having added these patterns, the expansion path in "expand_float" will
now try to use them for conversions from SImode to HFmode as there is no
floatsihf2 pattern. expand_float first tries widening the integer size and
looking for a match, so it will try SImode -> DImode. But our DI mode
pattern is going to then saturate us back to SImode which is wasteful.

Better, would be for us to provide float(uns)sihf2 patterns directly.
So that's what this patch does.

The testcase add in this patch would fail on trunk for AArch64. There is
no libgcc routine to make the conversion, and we don't provide appropriate
patterns in the backend, so we get a link-time error.

Bootstrapped and tested on aarch64-none-linux-gnu

OK for trunk?

Looks ok to me FWIW, but I can't approve.

Kyrill

James

---
2016-09-06  James Greenhalgh  <james.greenhalgh@arm.com>

	* config/aarch64/aarch64.md (<optab>sihf2): Convert to expand.
	(<optab>dihf2): Likewise.
	(aarch64_fp16_<optab><mode>hf2): New.

2016-09-06  James Greenhalgh  <james.greenhalgh@arm.com>

	* gcc.target/aarch64/floatdihf2_1.c: New.



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