[PATCH] D19178: Broaden FoldItoFPtoI to try and establish whether the integer value fits into the float type
Eli Friedman via llvm-commits
llvm-commits at lists.llvm.org
Sat Jul 30 19:53:51 PDT 2016
eli.friedman added inline comments.
================
Comment at: lib/Transforms/InstCombine/InstCombineCasts.cpp:1507
@@ +1506,3 @@
+ // then the conversion is undefined behavior.
+
+ Safe = BitRange <= SignificandWidth;
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Are you sure subtracting one actually makes the most significant bit zero-indexed? Normally, finding the distance between two array indexes is just simple subtraction; the extra "+1" looks weird. It's also kind of suspicious that your "zero-based" indexing can return a negative number (as an extreme case, if a 16-bit integer is all ones, your code says the most significant possibly set bit has index -1).
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Comment at: test/Transforms/InstCombine/sitofp.ll:278
@@ +277,3 @@
+; the right of the sign bit.
+; (Bits of %B: UUUUUUUUUUUUUUUUUUUUUUUU0000000000, U = unknown)
+; CHECK-LABEL: test27
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Maybe also add a corresponding test which doesn't fold?
https://reviews.llvm.org/D19178
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