[llvm] [ConstantFolding] Support ptrtoaddr in cast folds (PR #162480)

[Nikita Popov via llvm-commits]

https://github.com/nikic created https://github.com/llvm/llvm-project/pull/162480

We can support the same folds for as for ptrtoint. For the cast pair fold we just need to use the address type instead. The gep based folds were already operating on the address (aka index) width anyway.

>From ce6d9165f0bfed8d34d8f4a796cc252bce26c7de Mon Sep 17 00:00:00 2001
From: Nikita Popov <npopov at redhat.com>
Date: Wed, 8 Oct 2025 14:45:52 +0200
Subject: [PATCH] [ConstantFolding] Support ptrtoaddr in cast folds

We can support the same folds for as for ptrtoint. For the cast
pair fold we just need to use the address type instead. The gep
based folds were already operating on the address (aka index) width
anyway.
---
 llvm/lib/Analysis/ConstantFolding.cpp         | 13 +++---
 llvm/test/Transforms/InstCombine/ptrtoaddr.ll | 42 +++++++++++++++++--
 2 files changed, 45 insertions(+), 10 deletions(-)

diff --git a/llvm/lib/Analysis/ConstantFolding.cpp b/llvm/lib/Analysis/ConstantFolding.cpp
index b744537aeb474..4ee9b16235930 100755
--- a/llvm/lib/Analysis/ConstantFolding.cpp
+++ b/llvm/lib/Analysis/ConstantFolding.cpp
@@ -1495,17 +1495,17 @@ Constant *llvm::ConstantFoldCastOperand(unsigned Opcode, Constant *C,
   default:
     llvm_unreachable("Missing case");
   case Instruction::PtrToAddr:
-    // TODO: Add some of the ptrtoint folds here as well.
-    break;
   case Instruction::PtrToInt:
     if (auto *CE = dyn_cast<ConstantExpr>(C)) {
       Constant *FoldedValue = nullptr;
       // If the input is a inttoptr, eliminate the pair.  This requires knowing
       // the width of a pointer, so it can't be done in ConstantExpr::getCast.
       if (CE->getOpcode() == Instruction::IntToPtr) {
-        // zext/trunc the inttoptr to pointer size.
-        FoldedValue = ConstantFoldIntegerCast(CE->getOperand(0),
-                                              DL.getIntPtrType(CE->getType()),
+        // zext/trunc the inttoptr to pointer/address size.
+        Type *MidTy = Opcode == Instruction::PtrToInt
+                          ? DL.getAddressType(CE->getType())
+                          : DL.getIntPtrType(CE->getType());
+        FoldedValue = ConstantFoldIntegerCast(CE->getOperand(0), MidTy,
                                               /*IsSigned=*/false, DL);
       } else if (auto *GEP = dyn_cast<GEPOperator>(CE)) {
         // If we have GEP, we can perform the following folds:
@@ -1528,7 +1528,8 @@ Constant *llvm::ConstantFoldCastOperand(unsigned Opcode, Constant *C,
                 Sub->getOpcode() == Instruction::Sub &&
                 Sub->getOperand(0)->isNullValue())
               FoldedValue = ConstantExpr::getSub(
-                  ConstantExpr::getPtrToInt(Ptr, IntIdxTy), Sub->getOperand(1));
+                  ConstantExpr::getCast(Opcode, Ptr, IntIdxTy),
+                  Sub->getOperand(1));
           }
         }
       }
diff --git a/llvm/test/Transforms/InstCombine/ptrtoaddr.ll b/llvm/test/Transforms/InstCombine/ptrtoaddr.ll
index 61b13312521d2..4c3305b7903da 100644
--- a/llvm/test/Transforms/InstCombine/ptrtoaddr.ll
+++ b/llvm/test/Transforms/InstCombine/ptrtoaddr.ll
@@ -2,6 +2,12 @@
 ; RUN: opt < %s -passes=instcombine -S | FileCheck %s
 target datalayout = "p1:64:64:64:32"
 
+ at g = external global i8
+ at g2 = external global i8
+
+ at g.as1 = external addrspace(1) global i8
+ at g2.as1 = external addrspace(1) global i8
+
 define i32 @ptrtoaddr_inttoptr_arg(i32 %a) {
 ; CHECK-LABEL: define i32 @ptrtoaddr_inttoptr_arg(
 ; CHECK-SAME: i32 [[A:%.*]]) {
@@ -24,14 +30,14 @@ define i32 @ptrtoaddr_inttoptr() {
 
 define i32 @ptrtoaddr_inttoptr_diff_size1() {
 ; CHECK-LABEL: define i32 @ptrtoaddr_inttoptr_diff_size1() {
-; CHECK-NEXT:    ret i32 ptrtoaddr (ptr addrspace(1) inttoptr (i64 -1 to ptr addrspace(1)) to i32)
+; CHECK-NEXT:    ret i32 -1
 ;
   ret i32 ptrtoaddr (ptr addrspace(1) inttoptr (i64 -1 to ptr addrspace(1)) to i32)
 }
 
 define i32 @ptrtoaddr_inttoptr_diff_size2() {
 ; CHECK-LABEL: define i32 @ptrtoaddr_inttoptr_diff_size2() {
-; CHECK-NEXT:    ret i32 ptrtoaddr (ptr addrspace(1) inttoptr (i16 -1 to ptr addrspace(1)) to i32)
+; CHECK-NEXT:    ret i32 65535
 ;
   ret i32 ptrtoaddr (ptr addrspace(1) inttoptr (i16 -1 to ptr addrspace(1)) to i32)
 }
@@ -52,14 +58,42 @@ define i64 @ptr2addr2_inttoptr_noas2() {
 
 define i64 @ptrtoaddr_inttoptr_noas_diff_size1() {
 ; CHECK-LABEL: define i64 @ptrtoaddr_inttoptr_noas_diff_size1() {
-; CHECK-NEXT:    ret i64 ptrtoaddr (ptr inttoptr (i32 -1 to ptr) to i64)
+; CHECK-NEXT:    ret i64 4294967295
 ;
   ret i64 ptrtoaddr (ptr inttoptr (i32 -1 to ptr) to i64)
 }
 
 define i64 @ptrtoaddr_inttoptr_noas_diff_size2() {
 ; CHECK-LABEL: define i64 @ptrtoaddr_inttoptr_noas_diff_size2() {
-; CHECK-NEXT:    ret i64 ptrtoaddr (ptr inttoptr (i128 -1 to ptr) to i64)
+; CHECK-NEXT:    ret i64 -1
 ;
   ret i64 ptrtoaddr (ptr inttoptr (i128 -1 to ptr) to i64)
 }
+
+define i64 @ptrtoaddr_gep_null() {
+; CHECK-LABEL: define i64 @ptrtoaddr_gep_null() {
+; CHECK-NEXT:    ret i64 42
+;
+  ret i64 ptrtoaddr (ptr getelementptr (i8, ptr null, i64 42) to i64)
+}
+
+define i32 @ptrtoaddr_gep_null_addrsize() {
+; CHECK-LABEL: define i32 @ptrtoaddr_gep_null_addrsize() {
+; CHECK-NEXT:    ret i32 42
+;
+  ret i32 ptrtoaddr (ptr addrspace(1) getelementptr (i8, ptr addrspace(1) null, i32 42) to i32)
+}
+
+define i64 @ptrtoaddr_gep_sub() {
+; CHECK-LABEL: define i64 @ptrtoaddr_gep_sub() {
+; CHECK-NEXT:    ret i64 sub (i64 ptrtoaddr (ptr @g to i64), i64 ptrtoaddr (ptr @g2 to i64))
+;
+  ret i64 ptrtoaddr (ptr getelementptr (i8, ptr @g, i64 sub (i64 0, i64 ptrtoaddr (ptr @g2 to i64))) to i64)
+}
+
+define i32 @ptrtoaddr_gep_sub_addrsize() {
+; CHECK-LABEL: define i32 @ptrtoaddr_gep_sub_addrsize() {
+; CHECK-NEXT:    ret i32 sub (i32 ptrtoaddr (ptr addrspace(1) @g.as1 to i32), i32 ptrtoaddr (ptr addrspace(1) @g2.as1 to i32))
+;
+  ret i32 ptrtoaddr (ptr addrspace(1) getelementptr (i8, ptr addrspace(1) @g.as1, i32 sub (i32 0, i32 ptrtoaddr (ptr addrspace(1) @g2.as1 to i32))) to i32)
+}