[AsmPrinter] Allow lowerConstant() to strip address space casts

[krisb]

Summary

lowerConstant() doesn't expect AddrSpaceCast in an input expression
which can occur if IR is compiled for a SPIR target.

This patch allows lowerConstant() to strip address space casts here if they
haven't been resolved.

[krisb]

Ping

[yaxunl]

I think the lowering of addrspacecast is target dependent.

[krisb]

In D43186#1020602, @yaxunl wrote:

I think the lowering of addrspacecast is target dependent.

Yes, I'm absolutely agree.
But this is about to change the behavior from 'fail by default' to 'skip by default'.
Does it make sense?

[arsenm]

This is too aggressive. I have D20758 to do this for noon. Otherwise it should fail for the target to do something about it

[krisb]

In D43186#1020762, @arsenm wrote:

This is too aggressive. I have D20758 to do this for noon. Otherwise it should fail for the target to do something about it

Thanks. Are you going to commit D20758 patch?

lib/CodeGen/AsmPrinter/AsmPrinter.cpp

const MCExpr *AsmPrinter::lowerConstant(const Constant *CV) {
 
   case Instruction::Trunc:
     // We emit the value and depend on the assembler to truncate the generated
     // expression properly.  This is important for differences between
     // blockaddress labels.  Since the two labels are in the same function, it
     // is reasonable to treat their delta as a 32-bit value.
     LLVM_FALLTHROUGH;
   case Instruction::BitCast:
+  case Instruction::AddrSpaceCast:
     return lowerConstant(CE->getOperand(0));
 
   case Instruction::IntToPtr: {
     const DataLayout &DL = getDataLayout();
 
     // Handle casts to pointers by changing them into casts to the appropriate
     // integer type.  This promotes constant folding and simplifies this code.
     Constant *Op = CE->getOperand(0);

test/CodeGen/X86/constant-with-addrspace-cast.ll

+; RUN: llc -filetype=asm -mtriple x86_64 < %s
+
+; Check that the code below successfully compiled without getting
+; "LLVM ERROR: Unsupported expression in static initializer: addrspacecast"
+
+@__block_literal_global = external addrspace(1) constant { i32, i32, i8 addrspace(4)* }, align 4
+
+@block_A = addrspace(1) constant void (i8 addrspace(3)*) addrspace(4)* addrspacecast (void (i8 addrspace(3)*) addrspace(1)* bitcast ({ i32, i32, i8 addrspace(4)* } addrspace(1)* @__block_literal_global to void (i8 addrspace(3)*) addrspace(1)*) to void (i8 addrspace(3)*) addrspace(4)*), align 4