[PATCH] D74976: [CostModel][X86] Improve extract/insert element costs (PR43605)

[Simon Pilgrim via Phabricator via llvm-commits]

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


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Comment at: llvm/test/Analysis/CostModel/X86/vector-extract.ll:41
+; AVX-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %v8f64_3 = extractelement <8 x double> undef, i32 3
 ; AVX-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %v8f64_4 = extractelement <8 x double> undef, i32 4
+; AVX-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %v8f64_7 = extractelement <8 x double> undef, i32 7
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lebedev.ri wrote:
> Hm, why is this cost=0, don't we need to extract 3'th sub-register here?
AVX1/2 - this will legalize to 2 * <4 x double> to fit into ymm registers, so its already at index0 of the 2nd <4 x double>


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