[PATCH] D100149: [AMDGPU][GlobalISel] Legalize and select G_SBFX and G_UBFX

[Jay Foad via Phabricator via llvm-commits]

foad added inline comments.


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Comment at: llvm/lib/CodeGen/GlobalISel/GISelKnownBits.cpp:498-499
   }
+  case TargetOpcode::G_SBFX:
+  case TargetOpcode::G_UBFX: {
+    Register SrcReg = MI.getOperand(1).getReg();
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This should really go in as a separate patch with unit tests in unittests/CodeGen/GlobalISel/KnownBitsTest.cpp.


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Comment at: llvm/lib/CodeGen/GlobalISel/GISelKnownBits.cpp:518
+          /*Add*/ false, /*NSW*/ false, ExtKnown, WidthKnown);
+      Known = KnownBits::ashr(KnownBits::shl(Known, ShiftKnown), ShiftKnown);
+    }
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This looks technically correct but I can't help feeling you'd get more precise results (when Width isn't exactly known) from a specialized KnownBits::sext function. On the other hand, maybe it's not worth optimizing for the case where Width isn't exactly known.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D100149/new/

https://reviews.llvm.org/D100149