[llvm] r283323 - [Thumb] Don't try and emit LDRH/LDRB from the constant pool

[Friedman, Eli via llvm-commits]

On 10/5/2016 7:52 AM, James Molloy via llvm-commits wrote:
> Author: jamesm
> Date: Wed Oct  5 09:52:13 2016
> New Revision: 283323
>
> URL: http://llvm.org/viewvc/llvm-project?rev=283323&view=rev
> Log:
> [Thumb] Don't try and emit LDRH/LDRB from the constant pool
>
> This is not a valid encoding - these instructions cannot do PC-relative addressing.
>
> The underlying problem here is of whitelist in ARMISelDAGToDAG that unwraps ARMISD::Wrappers during addressing-mode selection. This didn't realise TargetConstantPool was actually possible, so didn't handle it.
>
> Added:
>      llvm/trunk/test/CodeGen/ARM/constantpool-promote-ldrh.ll
> Modified:
>      llvm/trunk/lib/Target/ARM/ARMISelDAGToDAG.cpp
>
> Modified: llvm/trunk/lib/Target/ARM/ARMISelDAGToDAG.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/ARM/ARMISelDAGToDAG.cpp?rev=283323&r1=283322&r2=283323&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Target/ARM/ARMISelDAGToDAG.cpp (original)
> +++ llvm/trunk/lib/Target/ARM/ARMISelDAGToDAG.cpp Wed Oct  5 09:52:13 2016
> @@ -1188,6 +1188,7 @@ ARMDAGToDAGISel::SelectThumbAddrModeImm5
>       } else if (N.getOpcode() == ARMISD::Wrapper &&
>           N.getOperand(0).getOpcode() != ISD::TargetGlobalAddress &&
>           N.getOperand(0).getOpcode() != ISD::TargetExternalSymbol &&
> +        N.getOperand(0).getOpcode() != ISD::TargetConstantPool &&
>           N.getOperand(0).getOpcode() != ISD::TargetGlobalTLSAddress) {
>         Base = N.getOperand(0);
>       } else {
>
> Added: llvm/trunk/test/CodeGen/ARM/constantpool-promote-ldrh.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/ARM/constantpool-promote-ldrh.ll?rev=283323&view=auto
> ==============================================================================
> --- llvm/trunk/test/CodeGen/ARM/constantpool-promote-ldrh.ll (added)
> +++ llvm/trunk/test/CodeGen/ARM/constantpool-promote-ldrh.ll Wed Oct  5 09:52:13 2016
> @@ -0,0 +1,22 @@
> +; RUN: llc < %s -O0 -fast-isel=false | FileCheck %s
> +; RUN: llc < %s -O0 -fast-isel=false -filetype=obj
> +target datalayout = "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64"
> +target triple = "thumbv6m-arm-linux-gnueabi"
> +
> + at fn1.a = private unnamed_addr constant [4 x i16] [i16 6, i16 0, i16 0, i16 0], align 2
> +
> +; We must not try and emit this bad instruction: "ldrh r1, .LCPI0_0"
> +; CHECK-LABEL: fn1:
> +; CHECK: adr [[base:r[0-9]+]], .LCPI0_0
> +; CHECK-NOT: ldrh {{r[0-9]+}}, .LCPI0_0
> +; FIXME: We want to use [[base]] below instead of "r0", but the preceding square bracket confuses FileCheck.
> +; CHECK: ldrh r{{[0-9]+}}, [r0]

You can write "ldrh r{{[0-9]+}}, {{\[}}[[base]]]".

-Eli

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