[PATCH] D109360: [ARM] Mark <= -1 immediate constant as cheap

[Dave Green via Phabricator via llvm-commits]

dmgreen added inline comments.


================
Comment at: llvm/lib/Target/ARM/ARMTargetTransformInfo.cpp:385
+  // We can convert <= -1 to < 0, which is generally quite cheap.
+  if (Inst && Opcode == Instruction::ICmp && Idx == 1 && Imm.isAllOnesValue()) {
+    ICmpInst::Predicate Pred = cast<ICmpInst>(Inst)->getPredicate();
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samtebbs wrote:
> Can this be applied to any integer less than the maximum for the type (e.g. <= 6 to < 7) rather than just <= -1 to < 0?
Yep! I originally had it that way, but unfortunately it led to more regressions. The combiner didn't always handle the constants better to actually produce smaller code.

The 0/-1 case should be the most common, I believe, and is at least the motivating case I have.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D109360/new/

https://reviews.llvm.org/D109360