forked from OSchip/llvm-project
405728fd47
In LLVM IR the following code:
%r = urem <ty> %t, %b
is equivalent to
%q = udiv <ty> %t, %b
%s = mul <ty> nuw %q, %b
%r = sub <ty> nuw %t, %q ; (t / b) * b + (t % b) = t
As UDiv, Mul and Sub are already supported by SCEV, URem can be implemented
with minimal effort using that relation:
%r --> (-%b * (%t /u %b)) + %t
We implement two special cases:
- if %b is 1, the result is always 0
- if %b is a power-of-two, we produce a zext/trunc based expression instead
That is, the following code:
%r = urem i32 %t, 65536
Produces:
%r --> (zext i16 (trunc i32 %a to i16) to i32)
Note that while this helps get a tighter bound on the range analysis and the
known-bits analysis, this exposes some normalization shortcoming of SCEVs:
%div = udim i32 %a, 65536
%mul = mul i32 %div, 65536
%rem = urem i32 %a, 65536
%add = add i32 %mul, %rem
Will usually not be reduced.
llvm-svn: 312329
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| .. | ||
| AliasSet | ||
| AssumptionCache | ||
| BasicAA | ||
| BlockFrequencyInfo | ||
| BranchProbabilityInfo | ||
| CFLAliasAnalysis | ||
| CallGraph | ||
| ConstantFolding | ||
| CostModel | ||
| Delinearization | ||
| DemandedBits | ||
| DependenceAnalysis | ||
| DivergenceAnalysis | ||
| DominanceFrontier | ||
| Dominators | ||
| GlobalsModRef | ||
| IVUsers | ||
| LazyCallGraph | ||
| LazyValueAnalysis | ||
| Lint | ||
| LoopAccessAnalysis | ||
| LoopInfo | ||
| MemoryDependenceAnalysis | ||
| MemorySSA | ||
| PostDominators | ||
| ProfileSummary | ||
| RegionInfo | ||
| ScalarEvolution | ||
| ScopedNoAliasAA | ||
| TypeBasedAliasAnalysis | ||
| ValueTracking | ||
| alias-analysis-uses.ll | ||