[InstCombine] Compare icmp inttoptr, inttoptr values directly

InstCombine already has some rules for `icmp ptrtoint, ptrtoint` to
drop the casts and compare the source values. This change adds the
same for the reverse case with `inttoptr`.

Author: citymarina

llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp

@@ -6081,12 +6081,12 @@ Instruction *InstCombinerImpl::foldICmpWithCastOp(ICmpInst &ICmp) {
 
   // Turn icmp (ptrtoint x), (ptrtoint/c) into a compare of the input if the
   // integer type is the same size as the pointer type.
-  auto CompatibleSizes = [&](Type *SrcTy, Type *DestTy) {
-    if (isa<VectorType>(SrcTy)) {
-      SrcTy = cast<VectorType>(SrcTy)->getElementType();
-      DestTy = cast<VectorType>(DestTy)->getElementType();
+  auto CompatibleSizes = [&](Type *PtrTy, Type *IntTy) {
+    if (isa<VectorType>(PtrTy)) {
+      PtrTy = cast<VectorType>(PtrTy)->getElementType();
+      IntTy = cast<VectorType>(IntTy)->getElementType();
     }
-    return DL.getPointerTypeSizeInBits(SrcTy) == DestTy->getIntegerBitWidth();
+    return DL.getPointerTypeSizeInBits(PtrTy) == IntTy->getIntegerBitWidth();
   };
   if (CastOp0->getOpcode() == Instruction::PtrToInt &&
       CompatibleSizes(SrcTy, DestTy)) {
@@ -6103,6 +6103,22 @@ Instruction *InstCombinerImpl::foldICmpWithCastOp(ICmpInst &ICmp) {
       return new ICmpInst(ICmp.getPredicate(), Op0Src, NewOp1);
   }
 
+  // Do the same in the other direction for icmp (inttoptr x), (inttoptr/c).
+  if (CastOp0->getOpcode() == Instruction::IntToPtr &&
+      CompatibleSizes(DestTy, SrcTy)) {
+    Value *NewOp1 = nullptr;
+    if (auto *IntToPtrOp1 = dyn_cast<IntToPtrInst>(ICmp.getOperand(1))) {
+      Value *IntSrc = IntToPtrOp1->getOperand(0);
+      if (IntSrc->getType() == Op0Src->getType())
+        NewOp1 = IntToPtrOp1->getOperand(0);
+    } else if (auto *RHSC = dyn_cast<Constant>(ICmp.getOperand(1))) {
+      NewOp1 = ConstantExpr::getPtrToInt(RHSC, SrcTy);
+    }
+
+    if (NewOp1)
+      return new ICmpInst(ICmp.getPredicate(), Op0Src, NewOp1);
+  }
+
   if (Instruction *R = foldICmpWithTrunc(ICmp))
     return R;
 

llvm/test/Transforms/InstCombine/icmp.ll

@@ -5326,3 +5326,22 @@ define i1 @pr94897(i32 range(i32 -2147483648, 0) %x) {
   %cmp = icmp ugt i32 %shl, -50331648
   ret i1 %cmp
 }
+
+define i1 @test_icmp_inttoptr(i64 %x, i64 %y) {
+; CHECK-LABEL: @test_icmp_inttoptr(
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i64 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    ret i1 [[CMP]]
+  %xptr = inttoptr i64 %x to ptr
+  %yptr = inttoptr i64 %y to ptr
+  %cmp = icmp eq ptr %xptr, %yptr
+  ret i1 %cmp
+}
+
+define i1 @test_icmp_inttoptr_constant(i64 %x) {
+; CHECK-LABEL: @test_icmp_inttoptr_constant(
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i64 [[X:%.*]], 42
+; CHECK-NEXT:    ret i1 [[CMP]]
+  %xptr = inttoptr i64 %x to ptr
+  %cmp = icmp eq ptr %xptr, inttoptr (i64 42 to ptr)
+  ret i1 %cmp
+}