[IndVars] Add check of loop invariant for indirect use

[Allen]

Summary

We usually only check direct use instruction of IV, while the
bitcast of 'ptrtoint ptr to i64' doesn't affect the result, so go
a step further.
Fix https://github.com/llvm/llvm-project/issues/59633.

[markoshorro]

LGTM

Thanks for taking the time to look at this.

llvm/lib/Transforms/Utils/SimplifyIndVar.cpp

while (!SimpleIVUsers.empty()) {
     // Bypass back edges to avoid extra work.
     if (UseInst == CurrIV) continue;
 
     // Try to replace UseInst with a loop invariant before any other
     // simplifications.
     if (replaceIVUserWithLoopInvariant(UseInst))
       continue;
 
+    // Go further for the bitcast ''prtoint ptr to i64'
+    if (isa<PtrToIntInst>(UseInst))
+      for (Use &U : UseInst->uses()) {
+        Instruction *User = cast<Instruction>(U.getUser());
+        if (replaceIVUserWithLoopInvariant(User))
+          break; // done replacing
+      }
+
     Instruction *IVOperand = UseOper.second;
     for (unsigned N = 0; IVOperand; ++N) {
       assert(N <= Simplified.size() && "runaway iteration");
       (void) N;
 
       Value *NewOper = foldIVUser(UseInst, IVOperand);
       if (!NewOper)
         break; // done folding

llvm/test/Transforms/IndVarSimplify/pr59633.ll

+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -passes=indvars -S | FileCheck %s
+
+declare void @foo(i64 noundef)
+
+; Function Attrs: mustprogress noreturn uwtable
+define void @pr59633(ptr noundef %ptr) {
+; CHECK-LABEL: @pr59633(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[PTR1:%.*]] = ptrtoint ptr [[PTR:%.*]] to i64
+; CHECK-NEXT:    [[TMP0:%.*]] = trunc i64 [[PTR1]] to i4
+; CHECK-NEXT:    [[TMP1:%.*]] = zext i4 [[TMP0]] to i64
+; CHECK-NEXT:    br label [[WHILE_BODY:%.*]]
+; CHECK:       while.body:
+; CHECK-NEXT:    tail call void @foo(i64 noundef [[TMP1]])
+; CHECK-NEXT:    br label [[WHILE_BODY]]
+;
+entry:
+  br label %while.body
+
+while.body:                                       ; preds = %entry, %while.body
+  %ptr.addr.0 = phi ptr [ %ptr, %entry ], [ %add.ptr, %while.body ]
+  %0 = ptrtoint ptr %ptr.addr.0 to i64
+  %and = and i64 %0, 15                           ; loop invariant
+  tail call void @foo(i64 noundef %and)
+  %add.ptr = getelementptr inbounds i8, ptr %ptr.addr.0, i64 16
+  br label %while.body
+}
+