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Hello, I am first time paying with SCEV codebase. I am trying to find out why ScalarEvolution is not able to give correct back edge taken count for an expression. So in my case flow reaches to howFarToZero() and in that function, I have following expressions as SCEV Start = (15 + (-1 * %i) (which is set to Distance SCEV) Step = 1 now, first of all, should I expect Start as ConstantSCEV (15) instead of the whole expression the problem here is getUnsignedRangeMax(Distance) returns very large number b...

...ev at lists.llvm.org> wrote: > > > > Hello, > > > > I am first time paying with SCEV codebase. > > I am trying to find out why ScalarEvolution is not able to give correct > back edge taken count for an expression. > > > > So in my case flow reaches to howFarToZero() and in that function, I > have following expressions as SCEV > > > > Start = (15 + (-1 * %i) (which is set to Distance SCEV) > > Step = 1 > > > > now, first of all, should I expect Start as ConstantSCEV (15) instead of > the whole expression > > the probl...

...e to fix that issue. > > > The backedge-taken count isn't nuw because nsw/nuw markings aren't > flow-sensitive: there isn't any way to mark the trip count as nuw without > marking every computation of `(long)n-2` as nuw. > > There's some code in ScalarEvolution::howFarToZero to try to refine the > max backedge-taken count in some cases, but it isn't very general. See > https://reviews.llvm.org/D28536 . > > -Eli > > -- > Employee of Qualcomm Innovation Center, Inc. > Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux...

Hello, If I run clang on the following code: void func(unsigned n) { > for (unsigned long x = 1; x < n; ++x) > dummy(x); > } I get the following llvm ir: define void @func(i32 %n) { > entry: > %conv = zext i32 %n to i64 > %cmp5 = icmp ugt i32 %n, 1 > br i1 %cmp5, label %for.body, label %for.cond.cleanup > for.cond.cleanup:

...; >> >> The backedge-taken count isn't nuw because nsw/nuw markings aren't >> flow-sensitive: there isn't any way to mark the trip count as nuw without >> marking every computation of `(long)n-2` as nuw. >> >> There's some code in ScalarEvolution::howFarToZero to try to refine the >> max backedge-taken count in some cases, but it isn't very general. See >> https://reviews.llvm.org/D28536 . >> >> -Eli >> >> -- >> Employee of Qualcomm Innovation Center, Inc. >> Qualcomm Innovation Center, Inc. is a membe...

...gt; The backedge-taken count isn't nuw because nsw/nuw markings aren't >>> flow-sensitive: there isn't any way to mark the trip count as nuw without >>> marking every computation of `(long)n-2` as nuw. >>> >>> There's some code in ScalarEvolution::howFarToZero to try to refine the >>> max backedge-taken count in some cases, but it isn't very general. See >>> https://reviews.llvm.org/D28536 . >>> >>> -Eli >>> >>> -- >>> Employee of Qualcomm Innovation Center, Inc. >>> Qualcomm In...