[PATCH] D36559: [ARM] Clarify legal addressing modes for ARM and Thumb2. NFC

[Eli Friedman via Phabricator via llvm-commits]

efriedma created this revision.
Herald added subscribers: kristof.beyls, javed.absar, aemerson.

The existing code is very clever, but not clear, which seems like the wrong tradeoff here.


Repository:
  rL LLVM

https://reviews.llvm.org/D36559

Files:
  lib/Target/ARM/ARMISelLowering.cpp


Index: lib/Target/ARM/ARMISelLowering.cpp
===================================================================
--- lib/Target/ARM/ARMISelLowering.cpp
+++ lib/Target/ARM/ARMISelLowering.cpp
@@ -12357,8 +12357,13 @@
     Scale = Scale & ~1;
     return Scale == 2 || Scale == 4 || Scale == 8;
   case MVT::i64:
+    // FIXME: What are we trying to model here? ldrd doesn't have an r + r
+    // version in Thumb mode.
     // r + r
-    if (((unsigned)AM.HasBaseReg + Scale) <= 2)
+    if (Scale == 1)
+      return true;
+    // r * 2 (this can be lowered to r + r).
+    if (!AM.HasBaseReg && Scale == 2)
       return true;
     return false;
   case MVT::isVoid:
@@ -12416,8 +12421,11 @@
       return isPowerOf2_32(Scale & ~1);
     case MVT::i16:
     case MVT::i64:
-      // r + r
-      if (((unsigned)AM.HasBaseReg + Scale) <= 2)
+      // r +/- r
+      if (Scale == 1 || (AM.HasBaseReg && Scale == -1))
+        return true;
+      // r * 2 (this can be lowered to r + r).
+      if (!AM.HasBaseReg && Scale == 2)
         return true;
       return false;
 


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