[llvm-branch-commits] [llvm] [DA] Remove special handling for SCEVAddExpr in GCD MIV (PR #169927)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-analysis

Author: Ryotaro Kasuga (kasuga-fj)

<details>
<summary>Changes</summary>

In `gcdMIVtest`, there is logic that assumes the addition(s) of `SCEVAddExpr` don't overflow without any checks. Adding overflow checks would be fine, but this part appeart to be less useful. So this patch removes it.

Fix one of the tests added in #<!-- -->169926.

---
Full diff: https://github.com/llvm/llvm-project/pull/169927.diff


2 Files Affected:

- (modified) llvm/lib/Analysis/DependenceAnalysis.cpp (-17) 
- (modified) llvm/test/Analysis/DependenceAnalysis/gcd-miv-overflow.ll (+4-5) 


``````````diff
diff --git a/llvm/lib/Analysis/DependenceAnalysis.cpp b/llvm/lib/Analysis/DependenceAnalysis.cpp
index 77b09fb15316e..bb54c0986c20f 100644
--- a/llvm/lib/Analysis/DependenceAnalysis.cpp
+++ b/llvm/lib/Analysis/DependenceAnalysis.cpp
@@ -2590,23 +2590,6 @@ bool DependenceInfo::gcdMIVtest(const SCEV *Src, const SCEV *Dst,
   const SCEV *Delta = SE->getMinusSCEV(DstConst, SrcConst);
   LLVM_DEBUG(dbgs() << "    Delta = " << *Delta << "\n");
   const SCEVConstant *Constant = dyn_cast<SCEVConstant>(Delta);
-  if (const SCEVAddExpr *Sum = dyn_cast<SCEVAddExpr>(Delta)) {
-    // If Delta is a sum of products, we may be able to make further progress.
-    for (const SCEV *Operand : Sum->operands()) {
-      if (isa<SCEVConstant>(Operand)) {
-        assert(!Constant && "Surprised to find multiple constants");
-        Constant = cast<SCEVConstant>(Operand);
-      } else if (const SCEVMulExpr *Product = dyn_cast<SCEVMulExpr>(Operand)) {
-        // Search for constant operand to participate in GCD;
-        // If none found; return false.
-        std::optional<APInt> ConstOp = getConstanCoefficient(Product);
-        if (!ConstOp)
-          return false;
-        ExtraGCD = APIntOps::GreatestCommonDivisor(ExtraGCD, ConstOp->abs());
-      } else
-        return false;
-    }
-  }
   if (!Constant)
     return false;
   APInt ConstDelta = cast<SCEVConstant>(Constant)->getAPInt();
diff --git a/llvm/test/Analysis/DependenceAnalysis/gcd-miv-overflow.ll b/llvm/test/Analysis/DependenceAnalysis/gcd-miv-overflow.ll
index 618d14c75faad..f6b23f18df738 100644
--- a/llvm/test/Analysis/DependenceAnalysis/gcd-miv-overflow.ll
+++ b/llvm/test/Analysis/DependenceAnalysis/gcd-miv-overflow.ll
@@ -127,9 +127,8 @@ exit:
 ;   A[-3*i - 3*m - INT64_MAX] = 1;
 ; }
 ;
-; FIXME: DependenceAnalysis currently detects no dependency between the two
-; stores, but it may exist. For example, consider `m = 1`. Then,
-; `-3*m - INT64_MAX` is `INT64_MAX - 1`. So `-3*i - 3*m - INT64_MAX` is
+; Dependency may exist between the two stores. For example, consider `m = 1`.
+; Then, `-3*m - INT64_MAX` is `INT64_MAX - 1`. So `-3*i - 3*m - INT64_MAX` is
 ; effectively `-3*i + (INT64_MAX - 1)`. Thus, accesses will be as follows:
 ;
 ;  memory access             | i == 1           | i == max_i - 1
@@ -143,7 +142,7 @@ define void @gcdmiv_const_ovfl(ptr %A, i64 %m) {
 ; CHECK-ALL-NEXT:  Src: store i8 0, ptr %gep.0, align 1 --> Dst: store i8 0, ptr %gep.0, align 1
 ; CHECK-ALL-NEXT:    da analyze - none!
 ; CHECK-ALL-NEXT:  Src: store i8 0, ptr %gep.0, align 1 --> Dst: store i8 1, ptr %gep.1, align 1
-; CHECK-ALL-NEXT:    da analyze - none!
+; CHECK-ALL-NEXT:    da analyze - output [*|<]!
 ; CHECK-ALL-NEXT:  Src: store i8 1, ptr %gep.1, align 1 --> Dst: store i8 1, ptr %gep.1, align 1
 ; CHECK-ALL-NEXT:    da analyze - none!
 ;
@@ -151,7 +150,7 @@ define void @gcdmiv_const_ovfl(ptr %A, i64 %m) {
 ; CHECK-GCD-MIV-NEXT:  Src: store i8 0, ptr %gep.0, align 1 --> Dst: store i8 0, ptr %gep.0, align 1
 ; CHECK-GCD-MIV-NEXT:    da analyze - consistent output [*]!
 ; CHECK-GCD-MIV-NEXT:  Src: store i8 0, ptr %gep.0, align 1 --> Dst: store i8 1, ptr %gep.1, align 1
-; CHECK-GCD-MIV-NEXT:    da analyze - none!
+; CHECK-GCD-MIV-NEXT:    da analyze - consistent output [*|<]!
 ; CHECK-GCD-MIV-NEXT:  Src: store i8 1, ptr %gep.1, align 1 --> Dst: store i8 1, ptr %gep.1, align 1
 ; CHECK-GCD-MIV-NEXT:    da analyze - consistent output [*]!
 ;

``````````

</details>


https://github.com/llvm/llvm-project/pull/169927