[PATCH] D39954: [IRCE] Smart range intersection

[Max Kazantsev via Phabricator via llvm-commits]

mkazantsev added inline comments.


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Comment at: lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp:1624
   //
   //   0 <= M + 1 * IndVar < L given L >= 0  (i.e. N == 1)
   //
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anna wrote:
> Could you please state here what exactly L stands for?
Here L denotes right border of the safe iteration space of the given range check. If there is no such border (e.g. the check was `iv > low`), it is in fact `SINT_MAX + 1`, but we strengthen it to `SINT_MAX`.



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Comment at: lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp:1658
+           "We can only substract from values in [0; SINT_MAX]!");
+    if (IsLatchSigned) {
+      // X is a number from signed range, Y is interpreted as signed.
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anna wrote:
> To clarify: In both cases - signed and unsigned latch, the SCEV subtraction and rules you have below will always give us a value in range [0, SINT_MAX], i.e. we will never cross the signed border.
> Here we are just "strengthening" the range and using unambiguous values for range intersection later on IRCE. 
It is not true. If we substract `-5` from `SINT_MAX` in unsigned case, we have a value greater than `SINT_MAX`.


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Comment at: lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp:1665
+      // If 0 <= -Y <= (SINT_MAX - X), we substract Y safely.
+      //   Rule 2: Y >=s (X - SINT_MA) ---> Y.
+      // If 0 <= (SINT_MAX - X) < -Y, we can only substract (X - SINT).
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anna wrote:
> SINT_MAX
Will fix.


https://reviews.llvm.org/D39954