[PATCH] D155386: [WebAssembly] Select BUILD_VECTOR with large unsigned lane values

[Thomas Lively via Phabricator via llvm-commits]

tlively added inline comments.


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Comment at: llvm/lib/Target/WebAssembly/WebAssemblyInstrSIMD.td:53
 def ImmI#SIZE : ImmLeaf<i32,
-  "return -(1 << ("#SIZE#" - 1)) <= Imm && Imm < (1 << ("#SIZE#" - 1));"
+  "return -(1 << ("#SIZE#" - 1)) <= Imm && Imm < (1 << "#SIZE#");"
 >;
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aheejin wrote:
> Why are the negative range and the positive range different?
The signed values range from -2^(n-1) to 2^(n-1)-1 and the unsigned values range from 0 to 2^n, so the union of the ranges is -2^(n-1) to 2^n. 

I realized this code will be UB and broken when SIZE is 64 because the 1 << 64 is nonsense, so I will have to fix and test that before I land this.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D155386/new/

https://reviews.llvm.org/D155386