[PATCH] D39108: [DAGCombine] Don't combine sext with extload if sextload is not supported and extload has multi users

[Guozhi Wei via Phabricator via llvm-commits]

Carrot updated this revision to Diff 120662.
Carrot marked 2 inline comments as done.

https://reviews.llvm.org/D39108

Files:
  lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  test/CodeGen/PowerPC/selectiondag-sextload.ll


Index: test/CodeGen/PowerPC/selectiondag-sextload.ll
===================================================================
--- test/CodeGen/PowerPC/selectiondag-sextload.ll
+++ test/CodeGen/PowerPC/selectiondag-sextload.ll
@@ -0,0 +1,26 @@
+; RUN: llc --mtriple=powerpc64le-linux-gnu < %s | FileCheck %s
+
+; It tests in function DAGCombiner::visitSIGN_EXTEND_INREG
+; signext will not be combined with extload, and causes extra zext.
+
+declare void @g(i32 signext)
+
+define void @foo(i8* %p) {
+entry:
+  br label %while.body
+
+while.body:
+  %0 = load i8, i8* %p, align 1
+  %conv = zext i8 %0 to i32
+  %cmp = icmp sgt i8 %0, 0
+  br i1 %cmp, label %if.then, label %while.body
+; CHECK:     lbz
+; CHECK:     extsb.
+; CHECK-NOT: rlwinm
+; CHECK:     ble
+
+if.then:
+  tail call void @g(i32 signext %conv)
+  br label %while.body
+}
+
Index: lib/CodeGen/SelectionDAG/DAGCombiner.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -8274,10 +8274,14 @@
   }
 
   // fold (sext_inreg (extload x)) -> (sextload x)
+  // If sextload is not supported by target, we can only do the combine when
+  // load has one use. Doing otherwise can block folding the extload with other
+  // extends that the target does support.
   if (ISD::isEXTLoad(N0.getNode()) &&
       ISD::isUNINDEXEDLoad(N0.getNode()) &&
       EVT == cast<LoadSDNode>(N0)->getMemoryVT() &&
-      ((!LegalOperations && !cast<LoadSDNode>(N0)->isVolatile()) ||
+      ((!LegalOperations && !cast<LoadSDNode>(N0)->isVolatile() &&
+        N0.hasOneUse()) ||
        TLI.isLoadExtLegal(ISD::SEXTLOAD, VT, EVT))) {
     LoadSDNode *LN0 = cast<LoadSDNode>(N0);
     SDValue ExtLoad = DAG.getExtLoad(ISD::SEXTLOAD, SDLoc(N), VT,


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D39108.120662.patch
Type: text/x-patch
Size: 1801 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20171027/2320d8a1/attachment.bin>