[llvm] [ARM] Validate STREX instruction in the assembler (PR #85074)

[via llvm-commits]

https://github.com/adamszilagyi created https://github.com/llvm/llvm-project/pull/85074

Based on the ARM Architecture Reference Manual:

```
**Use of R15** Specifying R15 for register <Rd>, <Rn>, or <Rm> has UNPREDICTABLE results.
**Operand restrictions** <Rd> must be distinct from both <Rm> and <Rn>, otherwise the results are UNPREDICTABLE.
```

>From 9191717aaa76c762ab48b51c3160138a098511f1 Mon Sep 17 00:00:00 2001
From: Adam Szilagyi <szilagyi.adam97 at gmail.com>
Date: Wed, 13 Mar 2024 14:23:36 +0100
Subject: [PATCH] [ARM] Validate STREX instruction in the assembler

---
 .../lib/Target/ARM/AsmParser/ARMAsmParser.cpp | 33 ++++++++++++
 llvm/test/MC/ARM/diagnostics.s                | 52 +++++++++++++++++++
 2 files changed, 85 insertions(+)

diff --git a/llvm/lib/Target/ARM/AsmParser/ARMAsmParser.cpp b/llvm/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
index c320bf723c88bb..8c96cce7a5cf55 100644
--- a/llvm/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
+++ b/llvm/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
@@ -7629,6 +7629,39 @@ bool ARMAsmParser::validateInstruction(MCInst &Inst,
     }
     return false;
   }
+  case ARM::t2STREXB:
+  case ARM::t2STREXH:
+  case ARM::t2STREX:
+  case ARM::STREXB:
+  case ARM::STREXH:
+  case ARM::STREX:
+  case ARM::STREXD: {
+    unsigned Rd = MRI->getEncodingValue(Inst.getOperand(0).getReg());
+    unsigned Rm = MRI->getEncodingValue(Inst.getOperand(1).getReg());
+    unsigned Rn = MRI->getEncodingValue(Inst.getOperand(2).getReg());
+
+    if (Rd == 15 || Rm == 15 || Rn == 15)
+      return Error(Operands[3]->getStartLoc(), "operand can't be R15");
+
+    if (Rd == Rm || Rd == Rn || (Opcode == ARM::STREXD && Rd == Rm + 1))
+      return Error(Operands[3]->getStartLoc(),
+                   "destination operand can't be identical to source operand");
+    return false;
+  }
+  case ARM::t2STREXD: {
+    unsigned Rd = MRI->getEncodingValue(Inst.getOperand(0).getReg());
+    unsigned Rm1 = MRI->getEncodingValue(Inst.getOperand(1).getReg());
+    unsigned Rm2 = MRI->getEncodingValue(Inst.getOperand(2).getReg());
+    unsigned Rn = MRI->getEncodingValue(Inst.getOperand(3).getReg());
+
+    if (Rd == 15 || Rn == 15)
+      return Error(Operands[4]->getStartLoc(), "operand can't be R15");
+
+    if (Rd == Rm1 || Rd == Rm2 || Rd == Rn)
+      return Error(Operands[4]->getStartLoc(),
+                   "destination operand can't be identical to source operand");
+    return false;
+  }
   case ARM::t2IT: {
     // Encoding is unpredictable if it ever results in a notional 'NV'
     // predicate. Since we don't parse 'NV' directly this means an 'AL'
diff --git a/llvm/test/MC/ARM/diagnostics.s b/llvm/test/MC/ARM/diagnostics.s
index e6d80ea7a6280c..f29be4e3bafcc8 100644
--- a/llvm/test/MC/ARM/diagnostics.s
+++ b/llvm/test/MC/ARM/diagnostics.s
@@ -336,6 +336,58 @@
 @ CHECK-ERRORS:         strexd  r6, r5, r3, [r8]
 @ CHECK-ERRORS:                         ^
 
+        @ Invalid Rm/Rn operands for strex
+        strex r1, r2, [r1]
+        strex r1, r1, [r2]
+
+@ CHECK-ERRORS: error: destination operand can't be identical to source operand
+@ CHECK-ERRORS:         strex r1, r2, [r1]
+@ CHECK-ERRORS:                     ^
+@ CHECK-ERRORS: error: destination operand can't be identical to source operand
+@ CHECK-ERRORS:         strex r1, r1, [r2]
+@ CHECK-ERRORS:                     ^
+
+        @ Can not use R15 as operand for strex
+        strex r15, r2, [r1]
+        strex r1, r15, [r2]
+        strex r1, r2, [r15]
+
+@ CHECK-ERRORS: error: operand can't be R15
+@ CHECK-ERRORS:         strex r15, r2, [r1]
+@ CHECK-ERRORS:                    ^
+@ CHECK-ERRORS: error: operand can't be R15
+@ CHECK-ERRORS:         strex r1, r15, [r2]
+@ CHECK-ERRORS:                   ^
+@ CHECK-ERRORS: error: operand can't be R15
+@ CHECK-ERRORS:         strex r1, r2, [r15]
+@ CHECK-ERRORS:                   ^
+
+        @ Can not use R15 as operand for strexd
+        strexd r15, r0, r1, [r6]
+        strexd r2, r0, r1, [r15]
+
+@ CHECK-ERRORS: error: operand can't be R15
+@ CHECK-ERRORS:         strexd r15, r0, r1, [r6]
+@ CHECK-ERRORS:                     ^
+@ CHECK-ERRORS: error: operand can't be R15
+@ CHECK-ERRORS:         strexd r2, r0, r1, [r15]
+@ CHECK-ERRORS:                    ^
+
+        @ Invalid Rm/Rn operands for strexd
+        strexd r1, r0, r1, [r6]
+        strexd r2, r2, r3, [r6]
+        strexd r4, r0, r1, [r4]
+
+@ CHECK-ERRORS: error: destination operand can't be identical to source operand
+@ CHECK-ERRORS:         strexd r1, r0, r1, [r6]
+@ CHECK-ERRORS:                    ^
+@ CHECK-ERRORS: error: destination operand can't be identical to source operand
+@ CHECK-ERRORS:         strexd r2, r2, r3, [r6]
+@ CHECK-ERRORS:                    ^
+@ CHECK-ERRORS: error: destination operand can't be identical to source operand
+@ CHECK-ERRORS:         strexd r4, r0, r1, [r4]
+@ CHECK-ERRORS:                        ^
+
         @ Illegal rotate operators for extend instructions
         sxtb r8, r3, #8
         sxtb r8, r3, ror 24