[AsmPrinter] Reject ptrtoint to larger size in lowerConstant()

[nikic]

Summary

When using a ptrtoint to a size larger than the pointer width in a global initializer, we currently create a ptr & low_bit_mask style MCExpr, which will later result in a relocation error during object file emission.

This patch rejects the constant expression already during lowerConstant(), which results in a much clearer error message that references the constant expression at fault.

This fixes https://github.com/llvm/llvm-project/issues/56400, for certain definitions of "fix".

[MaskRay]

Looks great!

llvm/test/CodeGen/X86/ptrtoint-constexpr-invalid.ll

2

Add a file-level comment that this is intentionally unsupported.

Otherwise from not --crash it is usually unclear whether it is a limitation or intentional.

llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp

case Instruction::PtrToInt: {
     // integer slot equal to the size of the pointer.
     //
     // If the pointer is larger than the resultant integer, then
     // as with Trunc just depend on the assembler to truncate it.
     if (DL.getTypeAllocSize(Ty).getFixedSize() <=
         DL.getTypeAllocSize(Op->getType()).getFixedSize())
       return OpExpr;
 
-    // Otherwise the pointer is smaller than the resultant integer, mask off
-    // the high bits so we are sure to get a proper truncation if the input is
-    // a constant expr.
-    unsigned InBits = DL.getTypeAllocSizeInBits(Op->getType());
-    const MCExpr *MaskExpr = MCConstantExpr::create(~0ULL >> (64-InBits), Ctx);
-    return MCBinaryExpr::createAnd(OpExpr, MaskExpr, Ctx);
+    break; // Error
   }
 
   case Instruction::Sub: {
     GlobalValue *LHSGV;
     APInt LHSOffset;
     DSOLocalEquivalent *DSOEquiv;
     if (IsConstantOffsetFromGlobal(CE->getOperand(0), LHSGV, LHSOffset,
                                    getDataLayout(), &DSOEquiv)) {

llvm/test/CodeGen/X86/ptrtoint-constexpr-invalid.ll

+; RUN: not --crash llc < %s -mtriple=i386-linux 2>&1 | FileCheck %s
+
+; ptrtoint expressions that cast to a wider integer type are not supported.
+; A frontend can achieve a similar result by casting to the correct integer
+; type and explicitly zeroing any additional bytes.
+; { i32, i32 } { i32 ptrtoint (ptr @r to i32), i32 0 }
+
+; CHECK: LLVM ERROR: Unsupported expression in static initializer: ptrtoint (ptr @r to i64)
+
+@r = global i64 ptrtoint (ptr @r to i64)

llvm/test/CodeGen/X86/ptrtoint-constexpr.ll

 ; RUN: llc < %s -mtriple=i386-linux | FileCheck %s
-  %union.x = type { i64 }
+  %union.x = type { i32 }
 
 ; CHECK:  .globl r
 ; CHECK: r:
-; CHECK: .quad  r&4294967295
+; CHECK: .long  r
 
-@r = global %union.x { i64 ptrtoint (ptr @r to i64) }, align 4
+@r = global %union.x { i32 ptrtoint (ptr @r to i32) }, align 4
 
 ; CHECK:  .globl x
 ; CHECK: x:
 ; CHECK: .quad  3
 
 @x = global i64 mul (i64 3, i64 ptrtoint (ptr getelementptr (i2, ptr null, i64 1) to i64))