[PATCH] D110488: [InstCombine] Fold ctpop((x & -x ) - 1) -> cttz(x, false) (PR51784)

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon created this revision.
RKSimon added reviewers: spatel, lebedev.ri.
Herald added a subscriber: hiraditya.
RKSimon requested review of this revision.
Herald added a project: LLVM.

Alive2: https://alive2.llvm.org/ce/z/8Yr3XG


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D110488

Files:
  llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
  llvm/test/Transforms/InstCombine/ctpop-cttz.ll


Index: llvm/test/Transforms/InstCombine/ctpop-cttz.ll
===================================================================
--- llvm/test/Transforms/InstCombine/ctpop-cttz.ll
+++ llvm/test/Transforms/InstCombine/ctpop-cttz.ll
@@ -94,11 +94,8 @@
 ; __builtin_popcount((i & -i) - 1) -> __builtin_cttz(i, false)
 define i32 @ctpop3(i32 %0) {
 ; CHECK-LABEL: @ctpop3(
-; CHECK-NEXT:    [[TMP2:%.*]] = sub i32 0, [[TMP0:%.*]]
-; CHECK-NEXT:    [[TMP3:%.*]] = and i32 [[TMP2]], [[TMP0]]
-; CHECK-NEXT:    [[TMP4:%.*]] = add i32 [[TMP3]], -1
-; CHECK-NEXT:    [[TMP5:%.*]] = tail call i32 @llvm.ctpop.i32(i32 [[TMP4]]), !range [[RNG0]]
-; CHECK-NEXT:    ret i32 [[TMP5]]
+; CHECK-NEXT:    [[TMP2:%.*]] = call i32 @llvm.cttz.i32(i32 [[TMP0:%.*]], i1 false), !range [[RNG0]]
+; CHECK-NEXT:    ret i32 [[TMP2]]
 ;
   %2 = sub i32 0, %0
   %3 = and i32 %2, %0
@@ -109,11 +106,8 @@
 
 define <2 x i32> @ctpop3v(<2 x i32> %0) {
 ; CHECK-LABEL: @ctpop3v(
-; CHECK-NEXT:    [[TMP2:%.*]] = sub <2 x i32> zeroinitializer, [[TMP0:%.*]]
-; CHECK-NEXT:    [[TMP3:%.*]] = and <2 x i32> [[TMP2]], [[TMP0]]
-; CHECK-NEXT:    [[TMP4:%.*]] = add <2 x i32> [[TMP3]], <i32 -1, i32 -1>
-; CHECK-NEXT:    [[TMP5:%.*]] = tail call <2 x i32> @llvm.ctpop.v2i32(<2 x i32> [[TMP4]])
-; CHECK-NEXT:    ret <2 x i32> [[TMP5]]
+; CHECK-NEXT:    [[TMP2:%.*]] = call <2 x i32> @llvm.cttz.v2i32(<2 x i32> [[TMP0:%.*]], i1 false)
+; CHECK-NEXT:    ret <2 x i32> [[TMP2]]
 ;
   %2 = sub <2 x i32> zeroinitializer, %0
   %3 = and <2 x i32> %2, %0
@@ -124,11 +118,8 @@
 
 define <2 x i32> @ctpop3v_undef(<2 x i32> %0) {
 ; CHECK-LABEL: @ctpop3v_undef(
-; CHECK-NEXT:    [[TMP2:%.*]] = sub <2 x i32> zeroinitializer, [[TMP0:%.*]]
-; CHECK-NEXT:    [[TMP3:%.*]] = and <2 x i32> [[TMP2]], [[TMP0]]
-; CHECK-NEXT:    [[TMP4:%.*]] = add <2 x i32> [[TMP3]], <i32 -1, i32 undef>
-; CHECK-NEXT:    [[TMP5:%.*]] = tail call <2 x i32> @llvm.ctpop.v2i32(<2 x i32> [[TMP4]])
-; CHECK-NEXT:    ret <2 x i32> [[TMP5]]
+; CHECK-NEXT:    [[TMP2:%.*]] = call <2 x i32> @llvm.cttz.v2i32(<2 x i32> [[TMP0:%.*]], i1 false)
+; CHECK-NEXT:    ret <2 x i32> [[TMP2]]
 ;
   %2 = sub <2 x i32> zeroinitializer, %0
   %3 = and <2 x i32> %2, %0
Index: llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -565,8 +565,11 @@
   }
 
   // ctpop(~x & (x - 1)) -> cttz(x, false)
+  // ctpop((x & -x ) - 1) -> cttz(x, false)
   if (match(Op0,
-            m_c_And(m_Not(m_Value(X)), m_Add(m_Deferred(X), m_AllOnes())))) {
+            m_c_And(m_Not(m_Value(X)), m_Add(m_Deferred(X), m_AllOnes()))) ||
+      match(Op0,
+            m_Add(m_c_And(m_Value(X), m_Neg(m_Deferred(X))), m_AllOnes()))) {
     Function *F =
         Intrinsic::getDeclaration(II.getModule(), Intrinsic::cttz, Ty);
     return CallInst::Create(F, {X, IC.Builder.getFalse()});


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