[llvm] [GVN] Add code to disable scalar PRE (PR #190386)

[Antonio Frighetto via llvm-commits]

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@@ -2029,12 +2037,15 @@ bool GVNPass::processNonLocalLoad(LoadInst *Load) {
   }
 
   bool Changed = false;
-  // If this load follows a GEP, see if we can PRE the indices before analyzing.
-  if (GetElementPtrInst *GEP =
-          dyn_cast<GetElementPtrInst>(Load->getOperand(0))) {
-    for (Use &U : GEP->indices())
-      if (Instruction *I = dyn_cast<Instruction>(U.get()))
-        Changed |= performScalarPRE(I);
+  // This is a limited form of scalar PRE for load indices. If this load follows
+  // a GEP, see if we can PRE the indices before analyzing.
+  if (isPREEnabled() && isScalarPREEnabled()) {
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antoniofrighetto wrote:

Hmm, I believe this should be land as an independent fix; not sure why this code was not guarded by isPREEnabled() before.

https://github.com/llvm/llvm-project/pull/190386