[llvm] [AMDGPU][SILoadStoreOptimizer] Try to find common base for L/Ss with 0 offset (PR #71126)

[Matt Arsenault via llvm-commits]

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@@ -2034,17 +2036,20 @@ void SILoadStoreOptimizer::processBaseWithConstOffset(const MachineOperand &Base
   if (Src0->isImm())
     std::swap(Src0, Src1);
 
-  if (!Src1->isImm())
-    return;
-
-  uint64_t Offset1 = Src1->getImm();
-  BaseHi = *Src0;
+  // If w,e are unable to find an offset by looking through BaseHi, then default
+  // to 0 offset with BaseHi as the base.
+  int64_t Offset1 = 0;
+  BaseHi = Def->getOperand(3);
+  if (Src1->isImm()) {
+    Offset1 = Src1->getImm();
+    BaseHi = *Src0;
+  }
 
   Addr.Base.LoReg = BaseLo.getReg();
   Addr.Base.HiReg = BaseHi.getReg();
   Addr.Base.LoSubReg = BaseLo.getSubReg();
   Addr.Base.HiSubReg = BaseHi.getSubReg();
-  Addr.Offset = (*Offset0P & 0x00000000ffffffff) | (Offset1 << 32);
+  Addr.Offset = (Offset0P & 0x00000000ffffffff) | (Offset1 << 32);
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arsenm wrote:

Offset1 may hit signed overflow, needs to cast to unsigned. Use Make_64

https://github.com/llvm/llvm-project/pull/71126