[PATCH] D96304: [Thumb2] support `movs pc, lr` alias for `subs pc, lr, #0`/`eret`

[Nick Desaulniers via Phabricator via llvm-commits]

nickdesaulniers created this revision.
nickdesaulniers added reviewers: rengolin, ostannard, psmith, rovka.
Herald added a subscriber: hiraditya.
nickdesaulniers requested review of this revision.
Herald added a project: LLVM.
Herald added a subscriber: llvm-commits.

This is used by the Linux kernel.

Forked from D95586 <https://reviews.llvm.org/D95586>.

Signed-off-by: Nick Desaulniers <ndesaulniers at google.com>


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D96304

Files:
  llvm/lib/Target/ARM/ARMInstrThumb2.td
  llvm/test/MC/ARM/lsl-zero-errors.s
  llvm/test/MC/ARM/thumb-mov.s


Index: llvm/test/MC/ARM/thumb-mov.s
===================================================================
--- llvm/test/MC/ARM/thumb-mov.s
+++ llvm/test/MC/ARM/thumb-mov.s
@@ -13,13 +13,11 @@
         movs pc, r0
         movs r0, pc
         movs pc, pc
-// CHECK: error: operand must be a register in range [r0, r14]
+// CHECK: error: invalid instruction, any one of the following would fix this:
 // CHECK-NEXT: movs pc, r0
-// CHECK: note: operand must be a register in range [r0, r14]
-// CHECK-NEXT: movs r0, pc
-// CHECK: note: invalid operand for instruction
+// CHECK: error: invalid instruction, any one of the following would fix this:
 // CHECK-NEXT: movs r0, pc
-// CHECK: error: invalid instruction
+// CHECK: error: invalid operand for instruction
 // CHECK-NEXT: movs pc, pc
 
         // mov.w selects t2MOVr
@@ -39,13 +37,11 @@
         movs.w pc, r0
         movs.w r0, pc
         movs.w pc, pc
-// CHECK: error: operand must be a register in range [r0, r14]
+// CHECK: error: invalid instruction, any one of the following would fix this:
 // CHECK-NEXT: movs.w pc, r0
-// CHECK: note: operand must be a register in range [r0, r14]
-// CHECK-NEXT: movs.w r0, pc
-// CHECK: note: invalid operand for instruction
+// CHECK: error: invalid instruction, any one of the following would fix this:
 // CHECK-NEXT: movs.w r0, pc
-// CHECK: error: invalid instruction
+// CHECK: error: invalid operand for instruction
 // CHECK-NEXT: movs.w pc, pc
 
 
@@ -104,3 +100,11 @@
         mov.w r0, sp
 // CHECK: mov.w sp, r0                @ encoding: [0x4f,0xea,0x00,0x0d]
 // CHECK: mov.w r0, sp                @ encoding: [0x4f,0xea,0x0d,0x00]
+
+        // `movs pc, lr` is an alias for `subs pc, lr, #0`.
+        movs   pc, lr
+        movs.w pc, lr
+// CHECK-V7: subs pc, lr, #0             @ encoding: [0xde,0xf3,0x00,0x8f]
+// CHECK-V7: subs pc, lr, #0             @ encoding: [0xde,0xf3,0x00,0x8f]
+// CHECK-V8: eret                        @ encoding: [0xde,0xf3,0x00,0x8f]
+// CHECK-V8: eret                        @ encoding: [0xde,0xf3,0x00,0x8f]
Index: llvm/test/MC/ARM/lsl-zero-errors.s
===================================================================
--- llvm/test/MC/ARM/lsl-zero-errors.s
+++ llvm/test/MC/ARM/lsl-zero-errors.s
@@ -72,8 +72,7 @@
 // CHECK-THUMBV7: note: operand must be a register in range [r0, r12] or r14
 // CHECK-THUMBV8: note: operand must be a register in range [r0, r14]
 
-// CHECK-THUMBV7: error: operand must be a register in range [r0, r12] or r14
-// CHECK-THUMBV8: error: operand must be a register in range [r0, r14]
+// CHECK-NONARM: error: invalid instruction, any one of the following would fix this:
 // CHECK-NONARM-NEXT: movs pc, r0, lsl #0
 
 // CHECK-NONARM: error: invalid instruction, any one of the following would fix this:
@@ -82,8 +81,7 @@
 // CHECK-NONARM: note: invalid operand for instruction
 // CHECK-NONARM: note: invalid operand for instruction
 
-// CHECK-THUMBV7: error: operand must be a register in range [r0, r12] or r14
-// CHECK-THUMBV8: error: operand must be a register in range [r0, r14]
+// CHECK-NONARM: error: invalid instruction, any one of the following would fix this:
 // CHECK-NONARM-NEXT: movs pc, pc, lsl #0
 
 // CHECK-ARM: mov pc, r0                @ encoding: [0x00,0xf0,0xa0,0xe1]
Index: llvm/lib/Target/ARM/ARMInstrThumb2.td
===================================================================
--- llvm/lib/Target/ARM/ARMInstrThumb2.td
+++ llvm/lib/Target/ARM/ARMInstrThumb2.td
@@ -4144,6 +4144,8 @@
   bits<8> imm;
   let Inst{7-0} = imm;
 }
+def : t2InstAlias<"movs{$p}\tpc, lr", (t2SUBS_PC_LR 0, pred:$p)>;
+def : t2InstAlias<"movs{$p}.w\tpc, lr", (t2SUBS_PC_LR 0, pred:$p)>;
 
 // Hypervisor Call is a system instruction.
 let isCall = 1 in {


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