[llvm] [DA] Remove base pointers from subscripts (PR #157083)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-analysis

Author: Ryotaro Kasuga (kasuga-fj)

<details>
<summary>Changes</summary>

This patch removes base pointers from subscripts when delinearization fails. Previously, in such cases, the pointer type SCEVs were used instead of offset SCEVs derived from them. For example, here is a portion of the debug output when analyzing `strong0` in `test/Analysis/DependenceAnalysis/StrongSIV.ll`:

```
testing subscript 0, SIV
    src = {(8 + %A),+,4}<nuw><%for.body>
    dst = {(8 + %A),+,4}<nuw><%for.body>
	Strong SIV test
	    Coeff = 4, i64
	    SrcConst = (8 + %A), ptr
	    DstConst = (8 + %A), ptr
	    Delta = 0, i64
	    UpperBound = (-1 + %n), i64
	    Distance = 0
	    Remainder = 0
```

As shown above, the `SrcConst` and `DstConst` are pointer values rather than integer offsets. `%A` should be removed.

This change is necessary for #<!-- -->157086, since `ScalarEvolution::willNotOverflow` expects integer type SCEVs as arguments.


---
Full diff: https://github.com/llvm/llvm-project/pull/157083.diff


1 Files Affected:

- (modified) llvm/lib/Analysis/DependenceAnalysis.cpp (+8-4) 


``````````diff
diff --git a/llvm/lib/Analysis/DependenceAnalysis.cpp b/llvm/lib/Analysis/DependenceAnalysis.cpp
index da86a8d2cc9c0..43eefc3120f9e 100644
--- a/llvm/lib/Analysis/DependenceAnalysis.cpp
+++ b/llvm/lib/Analysis/DependenceAnalysis.cpp
@@ -3698,8 +3698,8 @@ DependenceInfo::depends(Instruction *Src, Instruction *Dst,
 
   unsigned Pairs = 1;
   SmallVector<Subscript, 2> Pair(Pairs);
-  Pair[0].Src = SrcSCEV;
-  Pair[0].Dst = DstSCEV;
+  Pair[0].Src = SrcEv;
+  Pair[0].Dst = DstEv;
 
   if (Delinearize) {
     if (tryDelinearize(Src, Dst, Pair)) {
@@ -3709,6 +3709,8 @@ DependenceInfo::depends(Instruction *Src, Instruction *Dst,
   }
 
   for (unsigned P = 0; P < Pairs; ++P) {
+    assert(Pair[P].Src->getType()->isIntegerTy() && "Src must be an integer");
+    assert(Pair[P].Dst->getType()->isIntegerTy() && "Dst must be an integer");
     Pair[P].Loops.resize(MaxLevels + 1);
     Pair[P].GroupLoops.resize(MaxLevels + 1);
     Pair[P].Group.resize(Pairs);
@@ -4111,8 +4113,8 @@ const SCEV *DependenceInfo::getSplitIteration(const Dependence &Dep,
   SmallVector<Subscript, 2> Pair(Pairs);
   const SCEV *SrcSCEV = SE->getSCEV(SrcPtr);
   const SCEV *DstSCEV = SE->getSCEV(DstPtr);
-  Pair[0].Src = SrcSCEV;
-  Pair[0].Dst = DstSCEV;
+  Pair[0].Src = SE->removePointerBase(SrcSCEV);
+  Pair[0].Dst = SE->removePointerBase(DstSCEV);
 
   if (Delinearize) {
     if (tryDelinearize(Src, Dst, Pair)) {
@@ -4122,6 +4124,8 @@ const SCEV *DependenceInfo::getSplitIteration(const Dependence &Dep,
   }
 
   for (unsigned P = 0; P < Pairs; ++P) {
+    assert(Pair[P].Src->getType()->isIntegerTy() && "Src must be an integer");
+    assert(Pair[P].Dst->getType()->isIntegerTy() && "Dst must be an integer");
     Pair[P].Loops.resize(MaxLevels + 1);
     Pair[P].GroupLoops.resize(MaxLevels + 1);
     Pair[P].Group.resize(Pairs);

``````````

</details>


https://github.com/llvm/llvm-project/pull/157083