commit 5263bf583a26f3f99c2ac34843e89d210bb4fe26
author Mirko Brkusanin <Mirko.Brkusanin@amd.com> Tue Sep 07 16:18:19 2021 +0200
committer Mirko Brkusanin <Mirko.Brkusanin@amd.com> Tue Sep 07 16:33:24 2021 +0200
tree 4b8546da16b6f44d99ff8cc52e0ac8ec67e30d72
parent 0d48ee27749c79b260ce8ce0d047b52aef8a3435

[AMDGPU][GlobalISel] Legalization of G_ROTL and G_ROTR

Add implementation for the legalization of G_ROTL and G_ROTR machine
instructions. They are very similar to funnel shift instructions, the only
difference is funnel shifts have 3 operands, whereas rotate instructions have
two operands, the first being the register that is being rotated and the second
being the number of shifts. The legalization of G_ROTL/G_ROTR is just lowering
them into funnel shift instructions if they are legal.

Patch by: Mateja Marjanovic

Differential Revision: https://reviews.llvm.org/D105347

llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp

diff --git a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
index 315c199..ca7fe92 100644
--- a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
@@ -4434,6 +4434,8 @@
   case G_FMAXIMUM:
   case G_FSHL:
   case G_FSHR:
+  case G_ROTL:
+  case G_ROTR:
   case G_FREEZE:
   case G_SADDSAT:
   case G_SSUBSAT:
@@ -6079,6 +6081,27 @@
       isPowerOf2_32(EltSizeInBits))
     return lowerRotateWithReverseRotate(MI);
 
+  // If a funnel shift is supported, use it.
+  unsigned FShOpc = IsLeft ? TargetOpcode::G_FSHL : TargetOpcode::G_FSHR;
+  unsigned RevFsh = !IsLeft ? TargetOpcode::G_FSHL : TargetOpcode::G_FSHR;
+  bool IsFShLegal = false;
+  if ((IsFShLegal = LI.isLegalOrCustom({FShOpc, {DstTy, AmtTy}})) ||
+      LI.isLegalOrCustom({RevFsh, {DstTy, AmtTy}})) {
+    auto buildFunnelShift = [&](unsigned Opc, Register R1, Register R2,
+                                Register R3) {
+      MIRBuilder.buildInstr(Opc, {R1}, {R2, R2, R3});
+      MI.eraseFromParent();
+      return Legalized;
+    };
+    // If a funnel shift in the other direction is supported, use it.
+    if (IsFShLegal) {
+      return buildFunnelShift(FShOpc, Dst, Src, Amt);
+    } else if (isPowerOf2_32(EltSizeInBits)) {
+      Amt = MIRBuilder.buildNeg(DstTy, Amt).getReg(0);
+      return buildFunnelShift(RevFsh, Dst, Src, Amt);
+    }
+  }
+
   auto Zero = MIRBuilder.buildConstant(AmtTy, 0);
   unsigned ShOpc = IsLeft ? TargetOpcode::G_SHL : TargetOpcode::G_LSHR;
   unsigned RevShiftOpc = IsLeft ? TargetOpcode::G_LSHR : TargetOpcode::G_SHL;