[llvm] LAA: improve code in getStrideFromPointer (NFC) (PR #124780)

[Ramkumar Ramachandra via llvm-commits]

https://github.com/artagnon updated https://github.com/llvm/llvm-project/pull/124780

>From 616eb80f6ad24df568b05fc10ec15af1478e01b7 Mon Sep 17 00:00:00 2001
From: Ramkumar Ramachandra <ramkumar.ramachandra at codasip.com>
Date: Tue, 28 Jan 2025 16:16:51 +0000
Subject: [PATCH 1/3] LAA: improve code in getStrideFromPointer (NFC)

Strip dead code, inline a constant, and modernize style.
---
 llvm/lib/Analysis/LoopAccessAnalysis.cpp | 27 ++++++++----------------
 1 file changed, 9 insertions(+), 18 deletions(-)

diff --git a/llvm/lib/Analysis/LoopAccessAnalysis.cpp b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
index 697b40403902cc..aa3f108e24cb99 100644
--- a/llvm/lib/Analysis/LoopAccessAnalysis.cpp
+++ b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
@@ -2859,7 +2859,7 @@ static Value *stripGetElementPtr(Value *Ptr, ScalarEvolution *SE, Loop *Lp) {
 /// strides "a[i*stride]". Returns the symbolic stride, or null otherwise.
 static const SCEV *getStrideFromPointer(Value *Ptr, ScalarEvolution *SE, Loop *Lp) {
   auto *PtrTy = dyn_cast<PointerType>(Ptr->getType());
-  if (!PtrTy || PtrTy->isAggregateType())
+  if (!PtrTy)
     return nullptr;
 
   // Try to remove a gep instruction to make the pointer (actually index at this
@@ -2867,18 +2867,15 @@ static const SCEV *getStrideFromPointer(Value *Ptr, ScalarEvolution *SE, Loop *L
   // pointer, otherwise, we are analyzing the index.
   Value *OrigPtr = Ptr;
 
-  // The size of the pointer access.
-  int64_t PtrAccessSize = 1;
-
   Ptr = stripGetElementPtr(Ptr, SE, Lp);
   const SCEV *V = SE->getSCEV(Ptr);
 
   if (Ptr != OrigPtr)
     // Strip off casts.
-    while (const SCEVIntegralCastExpr *C = dyn_cast<SCEVIntegralCastExpr>(V))
+    while (auto *C = dyn_cast<SCEVIntegralCastExpr>(V))
       V = C->getOperand();
 
-  const SCEVAddRecExpr *S = dyn_cast<SCEVAddRecExpr>(V);
+  auto *S = dyn_cast<SCEVAddRecExpr>(V);
   if (!S)
     return nullptr;
 
@@ -2888,25 +2885,19 @@ static const SCEV *getStrideFromPointer(Value *Ptr, ScalarEvolution *SE, Loop *L
     return nullptr;
 
   V = S->getStepRecurrence(*SE);
-  if (!V)
-    return nullptr;
 
   // Strip off the size of access multiplication if we are still analyzing the
   // pointer.
   if (OrigPtr == Ptr) {
-    if (const SCEVMulExpr *M = dyn_cast<SCEVMulExpr>(V)) {
-      if (M->getOperand(0)->getSCEVType() != scConstant)
+    if (auto *M = dyn_cast<SCEVMulExpr>(V)) {
+      auto *StepConst = dyn_cast<SCEVConstant>(M->getOperand(0));
+      if (!StepConst)
         return nullptr;
 
-      const APInt &APStepVal = cast<SCEVConstant>(M->getOperand(0))->getAPInt();
-
-      // Huge step value - give up.
-      if (APStepVal.getBitWidth() > 64)
+      if (auto StepVal = StepConst->getAPInt().trySExtValue();
+          !StepVal || StepVal != 1)
         return nullptr;
 
-      int64_t StepVal = APStepVal.getSExtValue();
-      if (PtrAccessSize != StepVal)
-        return nullptr;
       V = M->getOperand(1);
     }
   }
@@ -2920,7 +2911,7 @@ static const SCEV *getStrideFromPointer(Value *Ptr, ScalarEvolution *SE, Loop *L
   if (isa<SCEVUnknown>(V))
     return V;
 
-  if (const auto *C = dyn_cast<SCEVIntegralCastExpr>(V))
+  if (auto *C = dyn_cast<SCEVIntegralCastExpr>(V))
     if (isa<SCEVUnknown>(C->getOperand()))
       return V;
 

>From 0a48a238c1a51c97fb9f721374c8e346e03c2bea Mon Sep 17 00:00:00 2001
From: Ramkumar Ramachandra <ramkumar.ramachandra at codasip.com>
Date: Fri, 31 Jan 2025 11:33:54 +0000
Subject: [PATCH 2/3] LAA: fix style; address review

---
 llvm/lib/Analysis/LoopAccessAnalysis.cpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/llvm/lib/Analysis/LoopAccessAnalysis.cpp b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
index aa3f108e24cb99..d2a8f859421a1a 100644
--- a/llvm/lib/Analysis/LoopAccessAnalysis.cpp
+++ b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
@@ -2894,8 +2894,8 @@ static const SCEV *getStrideFromPointer(Value *Ptr, ScalarEvolution *SE, Loop *L
       if (!StepConst)
         return nullptr;
 
-      if (auto StepVal = StepConst->getAPInt().trySExtValue();
-          !StepVal || StepVal != 1)
+      auto StepVal = StepConst->getAPInt().trySExtValue();
+      if (!StepVal || StepVal != 1)
         return nullptr;
 
       V = M->getOperand(1);

>From 7605406d1aeecf7a69c58df320674913a91d0a7f Mon Sep 17 00:00:00 2001
From: Ramkumar Ramachandra <ramkumar.ramachandra at codasip.com>
Date: Fri, 31 Jan 2025 15:37:18 +0000
Subject: [PATCH 3/3] LAA: add comment

---
 llvm/lib/Analysis/LoopAccessAnalysis.cpp | 1 +
 1 file changed, 1 insertion(+)

diff --git a/llvm/lib/Analysis/LoopAccessAnalysis.cpp b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
index d2a8f859421a1a..ac8a35fbc54fb1 100644
--- a/llvm/lib/Analysis/LoopAccessAnalysis.cpp
+++ b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
@@ -2895,6 +2895,7 @@ static const SCEV *getStrideFromPointer(Value *Ptr, ScalarEvolution *SE, Loop *L
         return nullptr;
 
       auto StepVal = StepConst->getAPInt().trySExtValue();
+      // Bail out on a non-unit pointer access size.
       if (!StepVal || StepVal != 1)
         return nullptr;