[PATCH] D63958: [SDAG] commute setcc operands to match a subtract

[Sanjay Patel via Phabricator via llvm-commits]

spatel marked an inline comment as done.
spatel added inline comments.


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Comment at: llvm/test/CodeGen/Lanai/sub-cmp-peephole.ll:28
 ; CHECK-NEXT:    sub.f %r7, %r6, %r3
-; CHECK-NEXT:    sel.lt %r3, %r0, %rv
+; CHECK-NEXT:    sel.gt %r3, %r0, %rv
 ; CHECK-NEXT:    ld -4[%fp], %pc ! return
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jpienaar wrote:
> The select compare changes, but the operands to the subtract doesn't, that seems weird.
If I'm reading this asm correctly based on the linked doc:
http://g.co/lanai/isa 

We have:
 %a == %r6 , %b == %r7
so "sub.f %r7, %r6, %r3" means "b-a" goes into %r3
And "sel.gt %r3, %r0, %rv" means "b-a" goes into "rv" if "b-a" was greater than 0.

That matches the IR logic, so is the code miscompiled without this patch? If we have "sel.lt", then that means the returned value is negative or zero rather than the intended positive or zero?


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  https://reviews.llvm.org/D63958/new/

https://reviews.llvm.org/D63958