[llvm] 1a1448e - [X86] Merge X86MCInstLowering's maxLongNopLength into emitNop and remove check for FeatureNOPL.

[Craig Topper via llvm-commits]

Author: Craig Topper
Date: 2020-07-25T22:11:47-07:00
New Revision: 1a1448e6568d9b11f198e510fa9c4cb6b1f4216a

URL: https://github.com/llvm/llvm-project/commit/1a1448e6568d9b11f198e510fa9c4cb6b1f4216a
DIFF: https://github.com/llvm/llvm-project/commit/1a1448e6568d9b11f198e510fa9c4cb6b1f4216a.diff

LOG: [X86] Merge X86MCInstLowering's maxLongNopLength into emitNop and remove check for FeatureNOPL.

The switch in emitNop uses 64-bit registers for nops exceeding
2 bytes. This isn't valid outside 64-bit mode. We could fix this
easily enough, but there are no users that ask for more than 2
bytes outside 64-bit mode.

Inlining the method to make the coupling between the two methods
more explicit.

Added: 
    

Modified: 
    llvm/lib/Target/X86/X86MCInstLower.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Target/X86/X86MCInstLower.cpp b/llvm/lib/Target/X86/X86MCInstLower.cpp
index b4db72e15060..8f3e32727371 100644
--- a/llvm/lib/Target/X86/X86MCInstLower.cpp
+++ b/llvm/lib/Target/X86/X86MCInstLower.cpp
@@ -1079,29 +1079,27 @@ void X86AsmPrinter::LowerTlsAddr(X86MCInstLower &MCInstLowering,
   }
 }
 
-/// Return the longest nop which can be efficiently decoded for the given
-/// target cpu.  15-bytes is the longest single NOP instruction, but some
-/// platforms can't decode the longest forms efficiently.
-static unsigned maxLongNopLength(const X86Subtarget *Subtarget) {
-  if (Subtarget->getFeatureBits()[X86::FeatureFast7ByteNOP])
-    return 7;
-  if (Subtarget->getFeatureBits()[X86::FeatureFast15ByteNOP])
-    return 15;
-  if (Subtarget->getFeatureBits()[X86::FeatureFast11ByteNOP])
-    return 11;
-  if (Subtarget->getFeatureBits()[X86::FeatureNOPL] || Subtarget->is64Bit())
-    return 10;
-  if (Subtarget->is32Bit())
-    return 2;
-  return 1;
-}
-
 /// Emit the largest nop instruction smaller than or equal to \p NumBytes
 /// bytes.  Return the size of nop emitted.
 static unsigned emitNop(MCStreamer &OS, unsigned NumBytes,
                         const X86Subtarget *Subtarget) {
+  unsigned MaxNopLength = 1;
+  if (Subtarget->is64Bit()) {
+    // FIXME: We can use NOOPL on 32-bit targets with FeatureNOPL, but the
+    // IndexReg/BaseReg below need to be updated.
+    if (Subtarget->hasFeature(X86::FeatureFast7ByteNOP))
+      MaxNopLength = 7;
+    else if (Subtarget->hasFeature(X86::FeatureFast15ByteNOP))
+      MaxNopLength = 15;
+    else if (Subtarget->hasFeature(X86::FeatureFast11ByteNOP))
+      MaxNopLength = 11;
+    else
+      MaxNopLength = 10;
+  } if (Subtarget->is32Bit())
+    MaxNopLength = 2;
+
   // Cap a single nop emission at the profitable value for the target
-  NumBytes = std::min(NumBytes, maxLongNopLength(Subtarget));
+  NumBytes = std::min(NumBytes, MaxNopLength);
 
   unsigned NopSize;
   unsigned Opc, BaseReg, ScaleVal, IndexReg, Displacement, SegmentReg;