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[AsmPrinter] Treat a narrowing PtrToInt like Trunc 

When printing assembly for PtrToInt, AsmPrinter::lowerConstant
incorrectly assumed that if PtrToInt was not converting to an
int with exactly the same number of bits, it must be widening
to a larger int. But this isn't necessarily true; PtrToInt can
also shrink the size, which is useful when you want to produce
a known 32-bit pointer on a 64-bit platform (on x86_64 ELF
this yields a R_X86_64_32 relocation).

The old behavior of falling through to the widening case for a
narrowing PtrToInt yields bogus assembly code like this, which
fails to assemble because the no-op bit and it accidentally
creates is not a valid relocation:

```
        .long   a&-1
```

The fix is to treat a narrowing PtrToInt exactly the same as
it already treats Trunc: just emit the expression and let
the assembler deal with truncating it in the appropriate way.

Patch by Mat Hostetter <mjh@fb.com>.

Differential Revision: https://reviews.llvm.org/D61325

llvm-svn: 361508
This commit is contained in:
Shoaib Meenai 2019-05-23 16:29:09 +00:00
parent 000228183b
commit 87226a7202
2 changed files with 10 additions and 1 deletions
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5
llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
View File

@ -2231,7 +2231,10 @@ const MCExpr *AsmPrinter::lowerConstant(const Constant *CV) {
// We can emit the pointer value into this slot if the slot is an // We can emit the pointer value into this slot if the slot is an
// integer slot equal to the size of the pointer. // integer slot equal to the size of the pointer.
if (DL.getTypeAllocSize(Ty) == DL.getTypeAllocSize(Op->getType())) //
// 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) <= DL.getTypeAllocSize(Op->getType()))
return OpExpr; return OpExpr;
// Otherwise the pointer is smaller than the resultant integer, mask off // Otherwise the pointer is smaller than the resultant integer, mask off

6
llvm/test/CodeGen/X86/ptrtoint-narrow.ll Normal file
View File

@ -0,0 +1,6 @@
; RUN: llc < %s -mtriple=x86_64-unknown-linux-gnu | FileCheck %s
@ptr = external global i8, align 1
@ref = constant i32 ptrtoint (i8* @ptr to i32), align 4
; CHECK: .long ptr{{$}}