[llvm-commits] value range analysis based on scalar-evolutions

[Devang Patel]

On Jun 1, 2008, at 8:54 PM, Nick Lewycky wrote:

> I've implemented an analysis pass that uses SCEV to determine value  
> ranges of integer-typed registers.
>
> Currently it maintains a map of Value* to ConstantRange*, which is  
> rather inelegant. I was thinking we could have one analysis which  
> would do that and others that would update the central analysis.
>
> I also implemented an optz'n pass based on it, but it hardly  
> optimized anything and as such is not included in this patch.
>
> Please comment!


+static RegisterPass<LoopVR> X("loopvr", "Loop Value Ranges");

You want to register this as an analysis pass and cfe-only pass.

+static SCEVHandle getTruncateOrZeroExtend(const SCEVHandle &V, const  
Type *Ty,
+                                          ScalarEvolution &SE) {

Why not move this into ScalarEvolution.h ?

+      APInt Spread_X = X.getSetSize(), Spread_Y = Y.getSetSize();
+      APInt NewLower = X.getLower() + Y.getLower(),
+            NewUpper = X.getUpper() + Y.getUpper() - 1;

nit-pick. I'd prefer to write this as

	APInt NewLower = ..;
	APInt NewUpper = ..;
	
+bool LoopVR::runOnFunction(Function &F) {

Is there a reason to not make this a LoopPass ?

+  for (LoopInfo::iterator I = LI.begin(), E = LI.end(); I != E; ++I) {
+    Loop *L = *I;

...

+        Loop *LL = LI.getLoopFor(*BI);
+        if (LL->isLoopInvariant(II)) continue;

Do you really want to check LL->isLoopInvariant(II) instead of L- 
 >isLoopInvariant(II) here ?


-
Devang