[PATCH] D99541: GlobalISel: Check for powers of 2 for inverse funnel shift lowering

[Matt Arsenault via Phabricator via llvm-commits]

arsenm created this revision.
arsenm added reviewers: foad, aemerson, paquette.
Herald added subscribers: hiraditya, rovka.
arsenm requested review of this revision.
Herald added a subscriber: wdng.
Herald added a project: LLVM.

This doesn't make a practical difference since it would only be broken
if a target actually had a legal non-power-of-2 inverse shift.


https://reviews.llvm.org/D99541

Files:
  llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp


Index: llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
===================================================================
--- llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
+++ llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
@@ -5248,6 +5248,10 @@
   LLT ShTy = MRI.getType(Z);
 
   unsigned BW = Ty.getScalarSizeInBits();
+
+  if (!isPowerOf2_32(BW))
+    return UnableToLegalize;
+
   const bool IsFSHL = MI.getOpcode() == TargetOpcode::G_FSHL;
   unsigned RevOpcode = IsFSHL ? TargetOpcode::G_FSHR : TargetOpcode::G_FSHL;
 
@@ -5346,8 +5350,13 @@
 
   bool IsFSHL = MI.getOpcode() == TargetOpcode::G_FSHL;
   unsigned RevOpcode = IsFSHL ? TargetOpcode::G_FSHR : TargetOpcode::G_FSHL;
-  if (LI.getAction({RevOpcode, {Ty, ShTy}}).Action == Lower)
-    return lowerFunnelShiftAsShifts(MI);
+  if (LI.getAction({RevOpcode, {Ty, ShTy}}).Action == Lower) {
+    // This only works for powers of 2, fallback to shifts if it fails.
+    LegalizerHelper::LegalizeResult Result = lowerFunnelShiftAsShifts(MI);
+    if (Result != UnableToLegalize)
+      return Result;
+  }
+
   return lowerFunnelShiftWithInverse(MI);
 }
 


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D99541.333985.patch
Type: text/x-patch
Size: 1120 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20210329/39adf257/attachment.bin>