[llvm] [X86] Match ENDBR immediates in little-endian order (PR #208754)

[Phoebe Wang via llvm-commits]

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@@ -926,22 +926,30 @@ static bool isCalleeLoad(SDValue Callee, SDValue &Chain, bool HasCallSeq) {
   }
 }
 
-static bool isEndbrImm64(uint64_t Imm) {
-// There may be some other prefix bytes between 0xF3 and 0x0F1EFA.
-// i.g: 0xF3660F1EFA, 0xF3670F1EFA
-  if ((Imm & 0x00FFFFFF) != 0x0F1EFA)
+static bool isEndbrImm(uint64_t Imm, unsigned BitWidth) {
+  assert(BitWidth <= 64 && BitWidth % 8 == 0 && "Unexpected immediate size");
+
+  const unsigned NumBytes = BitWidth / 8;
+  if (NumBytes < 4)
     return false;
 
-  uint8_t OptionalPrefixBytes [] = {0x26, 0x2e, 0x36, 0x3e, 0x64,
-                                    0x65, 0x66, 0x67, 0xf0, 0xf2};
-  int i = 24; // 24bit 0x0F1EFA has matched
-  while (i < 64) {
-    uint8_t Byte = (Imm >> i) & 0xFF;
-    if (Byte == 0xF3)
+  const uint8_t OptionalPrefixBytes[] = {0x26, 0x2e, 0x36, 0x3e, 0x64,
+                                         0x65, 0x66, 0x67, 0xf0, 0xf2};
+  uint8_t Bytes[8];
+  for (unsigned I = 0; I != NumBytes; ++I)
+    Bytes[I] = (Imm >> (I * 8)) & 0xFF;
+
+  for (unsigned I = 0; I + 3 < NumBytes; ++I) {
+    if (Bytes[I] != 0xf3)
+      continue;
+
+    unsigned J = I + 1;
+    while (J < NumBytes && llvm::is_contained(OptionalPrefixBytes, Bytes[J]))
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phoebewang wrote:

Lack tests for optional prefix.

https://github.com/llvm/llvm-project/pull/208754