[AsmParser] Fix crash when hex literal exceeds 16-bit float range (#172669)

Fixes #172650.

Author: milos1397

llvm/lib/AsmParser/LLLexer.cpp

@@ -1129,16 +1129,26 @@ lltok::Kind LLLexer::Lex0x() {
     HexToIntPair(TokStart+3, CurPtr, Pair);
     APFloatVal = APFloat(APFloat::PPCDoubleDouble(), APInt(128, Pair));
     return lltok::APFloat;
-  case 'H':
-    APFloatVal = APFloat(APFloat::IEEEhalf(),
-                         APInt(16,HexIntToVal(TokStart+3, CurPtr)));
+  case 'H': {
+    uint64_t Val = HexIntToVal(TokStart + 3, CurPtr);
+    if (!llvm::isUInt<16>(Val)) {
+      LexError("hexadecimal constant too large for half (16-bit)");
+      return lltok::Error;
+    }
+    APFloatVal = APFloat(APFloat::IEEEhalf(), APInt(16, Val));
     return lltok::APFloat;
-  case 'R':
+  }
+  case 'R': {
     // Brain floating point
-    APFloatVal = APFloat(APFloat::BFloat(),
-                         APInt(16, HexIntToVal(TokStart + 3, CurPtr)));
+    uint64_t Val = HexIntToVal(TokStart + 3, CurPtr);
+    if (!llvm::isUInt<16>(Val)) {
+      LexError("hexadecimal constant too large for bfloat (16-bit)");
+      return lltok::Error;
+    }
+    APFloatVal = APFloat(APFloat::BFloat(), APInt(16, Val));
     return lltok::APFloat;
   }
+  }
 }
 
 /// Lex tokens for a label or a numeric constant, possibly starting with -.

llvm/test/Assembler/hex-float-overflow.ll

@@ -0,0 +1,22 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 6
+; RUN: split-file %s %t
+; RUN: not opt -S -disable-output < %t/half.ll 2>&1 | FileCheck %s --check-prefix=HALF
+; RUN: not opt -S -disable-output < %t/bfloat.ll 2>&1 | FileCheck %s --check-prefix=BFLOAT
+
+; Test that providing a hex literal larger than 16 bits for half-precision
+; triggers a proper error message instead of a compiler crash.
+
+;--- half.ll
+define half @test_half_overflow() {
+; HALF: error: hexadecimal constant too large for half (16-bit)
+  %1 = fadd half 0xH5F2F00, 0xH0000
+  ret half %1
+}
+
+;--- bfloat.ll
+define bfloat @test_bfloat_overflow() {
+; BFLOAT: error: hexadecimal constant too large for bfloat (16-bit)
+  %1 = fadd bfloat 0xR5F2F00, 0xR0000
+  ret bfloat %1
+}
+