[PATCH] D141823: [SCEV] More precise trip multiples

[Nikita Popov via Phabricator via llvm-commits]

nikic added a comment.

Precommit tests please.



================
Comment at: llvm/lib/Analysis/ScalarEvolution.cpp:6317
+    return TZ >= BitWidth ? APInt::getZero(BitWidth)
+                          : APInt(BitWidth, 1).shl(TZ);
   }
----------------
APInt::getOneBitSet


================
Comment at: llvm/lib/Analysis/ScalarEvolution.cpp:6323
+    const SCEVTruncateExpr *T = cast<SCEVTruncateExpr>(S);
+    return getMaxConstantMultiple(T->getOperand()).trunc(BitWidth);
   }
----------------
I don't think this is correct. `trunc(X nuw* C)` is not, in general, the same as `trunc(X) nuw* trunc(C)`.


================
Comment at: llvm/lib/Analysis/ScalarEvolution.cpp:6372
+    // If there are no wrap guarantees, find the trailing bits, which is the
+    // miminum of its operands.
+    uint32_t TZ = getMinTrailingZeros(N->getOperand(0));
----------------
minimum


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https://reviews.llvm.org/D141823