[PATCH] D127439: [PowerPC] Fix combine step for shufflevector.

[Stefan Pintilie via Phabricator via llvm-commits]

stefanp created this revision.
stefanp added reviewers: lei, nemanjai.
Herald added subscribers: shchenz, kbarton, hiraditya.
Herald added a project: All.
stefanp requested review of this revision.
Herald added a project: LLVM.

The combine step for shufflevector will sometimes replace undef in the mask
with a defined value. This can cause an infinite loop in some cases as another
combine will then put the undef back in the mask.

This patch fixes the issue so that undefs are not replaced when doing a combine.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D127439

Files:
  llvm/lib/Target/PowerPC/PPCISelLowering.cpp


Index: llvm/lib/Target/PowerPC/PPCISelLowering.cpp
===================================================================
--- llvm/lib/Target/PowerPC/PPCISelLowering.cpp
+++ llvm/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -14972,24 +14972,36 @@
     // Example (even elements from first vector):
     // vector_shuffle<0,16,1,17,2,18,3,19,4,20,5,21,6,22,7,23> t1, <zero>
     if (Mask[0] < NumElts)
-      for (int i = 1, e = Mask.size(); i < e; i += 2)
+      for (int i = 1, e = Mask.size(); i < e; i += 2) {
+        if (ShuffV[i] < 0)
+          continue;
         ShuffV[i] = (ShuffV[i - 1] + NumElts);
+      }
     // Example (odd elements from first vector):
     // vector_shuffle<16,0,17,1,18,2,19,3,20,4,21,5,22,6,23,7> t1, <zero>
     else
-      for (int i = 0, e = Mask.size(); i < e; i += 2)
+      for (int i = 0, e = Mask.size(); i < e; i += 2) {
+        if (ShuffV[i] < 0)
+          continue;
         ShuffV[i] = (ShuffV[i + 1] + NumElts);
+      }
   } else {
     // Example (even elements from first vector):
     // vector_shuffle<0,16,1,17,2,18,3,19,4,20,5,21,6,22,7,23> <zero>, t1
     if (Mask[0] < NumElts)
-      for (int i = 0, e = Mask.size(); i < e; i += 2)
+      for (int i = 0, e = Mask.size(); i < e; i += 2) {
+        if (ShuffV[i] < 0)
+          continue;
         ShuffV[i] = ShuffV[i + 1] - NumElts;
+      }
     // Example (odd elements from first vector):
     // vector_shuffle<16,0,17,1,18,2,19,3,20,4,21,5,22,6,23,7> <zero>, t1
     else
-      for (int i = 1, e = Mask.size(); i < e; i += 2)
+      for (int i = 1, e = Mask.size(); i < e; i += 2) {
+        if (ShuffV[i] < 0)
+          continue;
         ShuffV[i] = ShuffV[i - 1] - NumElts;
+      }
   }
 
   // If the RHS has undefs, we need to remove them since we may have created


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D127439.435668.patch
Type: text/x-patch
Size: 1784 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20220609/35662fed/attachment.bin>