[x86] avoid printing unnecessary sign bits of hex immediates in asm comments (PR20347)

It would be better to check the valid/expected size of the immediate operand, but this is
generally better than what we print right now.

Differential Revision: http://reviews.llvm.org/D20385

llvm-svn: 271114

1 files changed, 13 insertions, 4 deletions

diff --git a/llvm/lib/Target/X86/InstPrinter/X86ATTInstPrinter.cpp b/llvm/lib/Target/X86/InstPrinter/X86ATTInstPrinter.cpp
index 855e108a2bc..3a5d056888a 100644
--- a/llvm/lib/Target/X86/InstPrinter/X86ATTInstPrinter.cpp
+++ b/llvm/lib/Target/X86/InstPrinter/X86ATTInstPrinter.cpp
@@ -165,16 +165,25 @@ void X86ATTInstPrinter::printOperand(const MCInst *MI, unsigned OpNo,
   if (Op.isReg()) {
     printRegName(O, Op.getReg());
   } else if (Op.isImm()) {
-    // Print X86 immediates as signed values.
+    // Print immediates as signed values.
     int64_t Imm = Op.getImm();
     O << markup("<imm:") << '$' << formatImm(Imm) << markup(">");
 
+    // TODO: This should be in a helper function in the base class, so it can
+    // be used by other printers.
+
     // If there are no instruction-specific comments, add a comment clarifying
     // the hex value of the immediate operand when it isn't in the range
     // [-256,255].
-    if (CommentStream && !HasCustomInstComment && (Imm > 255 || Imm < -256))
-      *CommentStream << format("imm = 0x%" PRIX64 "\n", (uint64_t)Imm);
-
+    if (CommentStream && !HasCustomInstComment && (Imm > 255 || Imm < -256)) {
+      // Don't print unnecessary hex sign bits. 
+      if (Imm == (int16_t)(Imm))
+        *CommentStream << format("imm = 0x%" PRIX16 "\n", (uint16_t)Imm);
+      else if (Imm == (int32_t)(Imm))
+        *CommentStream << format("imm = 0x%" PRIX32 "\n", (uint32_t)Imm);
+      else
+        *CommentStream << format("imm = 0x%" PRIX64 "\n", (uint64_t)Imm);
+    }
   } else {
     assert(Op.isExpr() && "unknown operand kind in printOperand");
     O << markup("<imm:") << '$';