[PATCH] D25521: [PPC] Shorter sequence to load 64bit constant with same hi/lo words

[Guozhi Wei via llvm-commits]

Carrot updated this revision to Diff 74452.
Carrot marked an inline comment as done.
Carrot added a comment.

Updated the test case with full related code sequence.


https://reviews.llvm.org/D25521

Files:
  lib/Target/PowerPC/PPCISelDAGToDAG.cpp
  test/CodeGen/PowerPC/pr30640.ll


Index: test/CodeGen/PowerPC/pr30640.ll
===================================================================
--- test/CodeGen/PowerPC/pr30640.ll
+++ test/CodeGen/PowerPC/pr30640.ll
@@ -0,0 +1,11 @@
+; RUN: llc -O2  -march=ppc64 -mcpu=pwr8 < %s | FileCheck %s
+
+define i64 @foo() {
+entry:
+  ret i64 -3617008641903833651
+
+; CHECK: lis 3, -12851
+; CHECK: ori 3, 3, 52685
+; CHECK: rldimi 3, 3, 32, 0
+}
+
Index: lib/Target/PowerPC/PPCISelDAGToDAG.cpp
===================================================================
--- lib/Target/PowerPC/PPCISelDAGToDAG.cpp
+++ lib/Target/PowerPC/PPCISelDAGToDAG.cpp
@@ -633,6 +633,13 @@
   // If no shift, we're done.
   if (!Shift) return Result;
 
+  // If Hi word == Lo word,
+  // we can use rldimi to insert the Lo word into Hi word.
+  if ((unsigned)(Imm & 0xFFFFFFFF) == Remainder) {
+    ++Result;
+    return Result;
+  }
+
   // Shift for next step if the upper 32-bits were not zero.
   if (Imm)
     ++Result;
@@ -731,6 +738,14 @@
   // If no shift, we're done.
   if (!Shift) return Result;
 
+  // If Hi word == Lo word,
+  // we can use rldimi to insert the Lo word into Hi word.
+  if ((unsigned)(Imm & 0xFFFFFFFF) == Remainder) {
+    SDValue Ops[] =
+      { SDValue(Result, 0), SDValue(Result, 0), getI32Imm(Shift), getI32Imm(0)};
+    return CurDAG->getMachineNode(PPC::RLDIMI, dl, MVT::i64, Ops);
+  }
+
   // Shift for next step if the upper 32-bits were not zero.
   if (Imm) {
     Result = CurDAG->getMachineNode(PPC::RLDICR, dl, MVT::i64,
@@ -1659,9 +1674,12 @@
 
       unsigned NumRLInsts = 0;
       bool FirstBG = true;
+      bool MoreBG = false;
       for (auto &BG : BitGroups) {
-        if (!MatchingBG(BG))
+        if (!MatchingBG(BG)) {
+          MoreBG = true;
           continue;
+        }
         NumRLInsts +=
           SelectRotMask64Count(BG.RLAmt, BG.Repl32, BG.StartIdx, BG.EndIdx,
                                !FirstBG);
@@ -1679,7 +1697,10 @@
       // because that exposes more opportunities for CSE.
       if (NumAndInsts > NumRLInsts)
         continue;
-      if (Use32BitInsts && NumAndInsts == NumRLInsts)
+      // When merging multiple bit groups, instruction or is used.
+      // But when rotate is used, rldimi can inert the rotated value into any
+      // register, so instruction or can be avoided.
+      if ((Use32BitInsts || MoreBG) && NumAndInsts == NumRLInsts)
         continue;
 
       DEBUG(dbgs() << "\t\t\t\tusing masking\n");


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