[PATCH] D101257: [InstCombine] C - ctpop(a) - > ctpop(~a)) if C is bitwidth (PR50104)

[Dávid Bolvanský via Phabricator via llvm-commits]

xbolva00 created this revision.
xbolva00 added reviewers: spatel, nikic.
Herald added a subscriber: hiraditya.
xbolva00 requested review of this revision.
Herald added a project: LLVM.
Herald added a subscriber: llvm-commits.

Proof: https://alive2.llvm.org/ce/z/mncA9K
Solves https://bugs.llvm.org/show_bug.cgi?id=50104


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D101257

Files:
  llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
  llvm/test/Transforms/InstCombine/ctpop.ll


Index: llvm/test/Transforms/InstCombine/ctpop.ll
===================================================================
--- llvm/test/Transforms/InstCombine/ctpop.ll
+++ llvm/test/Transforms/InstCombine/ctpop.ll
@@ -292,9 +292,9 @@
 
 define i8 @sub_ctpop(i8 %a)  {
 ; CHECK-LABEL: @sub_ctpop(
-; CHECK-NEXT:    [[CNT:%.*]] = tail call i8 @llvm.ctpop.i8(i8 [[A:%.*]]), !range [[RNG0]]
-; CHECK-NEXT:    [[RES:%.*]] = sub nuw nsw i8 8, [[CNT]]
-; CHECK-NEXT:    ret i8 [[RES]]
+; CHECK-NEXT:    [[TMP1:%.*]] = xor i8 [[A:%.*]], -1
+; CHECK-NEXT:    [[TMP2:%.*]] = call i8 @llvm.ctpop.i8(i8 [[TMP1]]), !range [[RNG0]]
+; CHECK-NEXT:    ret i8 [[TMP2]]
 ;
   %cnt = tail call i8 @llvm.ctpop.i8(i8 %a)
   %res = sub i8 8, %cnt
@@ -325,9 +325,9 @@
 
 define <2 x i32> @sub_ctpop_vec(<2 x i32> %a) {
 ; CHECK-LABEL: @sub_ctpop_vec(
-; CHECK-NEXT:    [[CNT:%.*]] = tail call <2 x i32> @llvm.ctpop.v2i32(<2 x i32> [[A:%.*]])
-; CHECK-NEXT:    [[RES:%.*]] = sub nuw nsw <2 x i32> <i32 32, i32 32>, [[CNT]]
-; CHECK-NEXT:    ret <2 x i32> [[RES]]
+; CHECK-NEXT:    [[TMP1:%.*]] = xor <2 x i32> [[A:%.*]], <i32 -1, i32 -1>
+; CHECK-NEXT:    [[TMP2:%.*]] = call <2 x i32> @llvm.ctpop.v2i32(<2 x i32> [[TMP1]])
+; CHECK-NEXT:    ret <2 x i32> [[TMP2]]
 ;
   %cnt = tail call <2 x i32> @llvm.ctpop.v2i32(<2 x i32> %a)
   %res = sub <2 x i32> <i32 32, i32 32>, %cnt
Index: llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -2112,6 +2112,13 @@
     return replaceInstUsesWith(
         I, Builder.CreateIntrinsic(Intrinsic::umin, {I.getType()}, {Op0, Y}));
 
+  // C - ctpop(X) => ctpop(~X) if C is bitwidth
+  if (match(Op0, m_SpecificInt(Ty->getScalarSizeInBits())) &&
+      match(Op1, m_OneUse(m_Intrinsic<Intrinsic::ctpop>(m_Value(X)))))
+    return replaceInstUsesWith(
+        I, Builder.CreateIntrinsic(Intrinsic::ctpop, {I.getType()},
+                                   {Builder.CreateNot(X)}));
+
   return TryToNarrowDeduceFlags();
 }
 


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