[llvm] eeb1256 - [InstSimplify] Slightly optimize simplifyLoad() (NFC)

[Nikita Popov via llvm-commits]

Author: Nikita Popov
Date: 2023-02-16T10:41:23+01:00
New Revision: eeb125659c172f83c9c3a7b5dfaf3e4fb54b7c25

URL: https://github.com/llvm/llvm-project/commit/eeb125659c172f83c9c3a7b5dfaf3e4fb54b7c25
DIFF: https://github.com/llvm/llvm-project/commit/eeb125659c172f83c9c3a7b5dfaf3e4fb54b7c25.diff

LOG: [InstSimplify] Slightly optimize simplifyLoad() (NFC)

Check upfront whether the load is based on a constant global
with definitive initializer. Don't bother computing offsets
otherwise.

Added: 
    

Modified: 
    llvm/lib/Analysis/InstructionSimplify.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index 865cd47b1ab7..372448b06472 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -6577,22 +6577,27 @@ static Value *simplifyLoadInst(LoadInst *LI, Value *PtrOp,
   if (LI->isVolatile())
     return nullptr;
 
-  APInt Offset(Q.DL.getIndexTypeSizeInBits(PtrOp->getType()), 0);
-  auto *PtrOpC = dyn_cast<Constant>(PtrOp);
+  if (auto *PtrOpC = dyn_cast<Constant>(PtrOp))
+    return ConstantFoldLoadFromConstPtr(PtrOpC, LI->getType(), Q.DL);
+
+  // We can only fold the load if it is from a constant global with definitive
+  // initializer. Skip expensive logic if this is not the case.
+  auto *GV = dyn_cast<GlobalVariable>(getUnderlyingObject(PtrOp));
+  if (!GV || !GV->isConstant() || !GV->hasDefinitiveInitializer())
+    return nullptr;
+
   // Try to convert operand into a constant by stripping offsets while looking
-  // through invariant.group intrinsics. Don't bother if the underlying object
-  // is not constant, as calculating GEP offsets is expensive.
-  if (!PtrOpC && isa<Constant>(getUnderlyingObject(PtrOp))) {
-    PtrOp = PtrOp->stripAndAccumulateConstantOffsets(
-        Q.DL, Offset, /* AllowNonInbounts */ true,
-        /* AllowInvariantGroup */ true);
+  // through invariant.group intrinsics.
+  APInt Offset(Q.DL.getIndexTypeSizeInBits(PtrOp->getType()), 0);
+  PtrOp = PtrOp->stripAndAccumulateConstantOffsets(
+      Q.DL, Offset, /* AllowNonInbounts */ true,
+      /* AllowInvariantGroup */ true);
+  if (PtrOp == GV) {
     // Index size may have changed due to address space casts.
     Offset = Offset.sextOrTrunc(Q.DL.getIndexTypeSizeInBits(PtrOp->getType()));
-    PtrOpC = dyn_cast<Constant>(PtrOp);
+    return ConstantFoldLoadFromConstPtr(GV, LI->getType(), Offset, Q.DL);
   }
 
-  if (PtrOpC)
-    return ConstantFoldLoadFromConstPtr(PtrOpC, LI->getType(), Offset, Q.DL);
   return nullptr;
 }