[PATCH] D109786: [SCEV] (udiv X, Y) * Y is always NUW

[Philip Reames via Phabricator via llvm-commits]

reames created this revision.
reames added reviewers: nikic, fhahn, mkazantsev, efriedma.
Herald added subscribers: bollu, hiraditya, mcrosier.
reames requested review of this revision.
Herald added a project: LLVM.

Motivated by the removal done in D109782 <https://reviews.llvm.org/D109782>.  This implements the correct flag part generically.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D109786

Files:
  llvm/lib/Analysis/ScalarEvolution.cpp
  llvm/test/Analysis/ScalarEvolution/extract-highbits-variablemask.ll
  llvm/test/Analysis/ScalarEvolution/mul.ll


Index: llvm/test/Analysis/ScalarEvolution/mul.ll
===================================================================
--- /dev/null
+++ llvm/test/Analysis/ScalarEvolution/mul.ll
@@ -0,0 +1,16 @@
+; NOTE: Assertions have been autogenerated by utils/update_analyze_test_checks.py
+; RUN: opt < %s "-passes=print<scalar-evolution>" -disable-output 2>&1 | FileCheck %s
+
+define i8 @test(i8 %x, i8 %y) {
+; CHECK-LABEL: 'test'
+; CHECK-NEXT:  Classifying expressions for: @test
+; CHECK-NEXT:    %udiv = udiv i8 %x, %y
+; CHECK-NEXT:    --> (%x /u %y) U: full-set S: full-set
+; CHECK-NEXT:    %res = mul i8 %udiv, %y
+; CHECK-NEXT:    --> ((%x /u %y) * %y)<nuw> U: full-set S: full-set
+; CHECK-NEXT:  Determining loop execution counts for: @test
+;
+  %udiv = udiv i8 %x, %y
+  %res = mul i8 %udiv, %y
+  ret i8 %res
+}
Index: llvm/test/Analysis/ScalarEvolution/extract-highbits-variablemask.ll
===================================================================
--- llvm/test/Analysis/ScalarEvolution/extract-highbits-variablemask.ll
+++ llvm/test/Analysis/ScalarEvolution/extract-highbits-variablemask.ll
@@ -10,7 +10,7 @@
 ; CHECK-NEXT:    %tmp1 = udiv i32 %val, %num
 ; CHECK-NEXT:    -->  (%val /u %num) U: full-set S: full-set
 ; CHECK-NEXT:    %tmp2 = mul i32 %tmp1, %num
-; CHECK-NEXT:    -->  ((%val /u %num) * %num) U: full-set S: full-set
+; CHECK-NEXT:    -->  ((%val /u %num) * %num)<nuw> U: full-set S: full-set
 ; CHECK-NEXT:  Determining loop execution counts for: @div
 ;
   %tmp1 = udiv i32 %val, %num
Index: llvm/lib/Analysis/ScalarEvolution.cpp
===================================================================
--- llvm/lib/Analysis/ScalarEvolution.cpp
+++ llvm/lib/Analysis/ScalarEvolution.cpp
@@ -2397,6 +2397,14 @@
       Ops[0]->isZero() && IsKnownNonNegative(Ops[1]))
     Flags = ScalarEvolution::setFlags(Flags, SCEV::FlagNUW);
 
+  // (udiv X, Y) * Y is always NUW
+  if (Type == scMulExpr && !ScalarEvolution::hasFlags(Flags, SCEV::FlagNUW) &&
+      Ops.size() == 2) {
+    auto *UDiv = dyn_cast<SCEVUDivExpr>(Ops[0]);
+    if (UDiv && UDiv->getNumOperands() == 2 && UDiv->getOperand(1) == Ops[1])
+      Flags = ScalarEvolution::setFlags(Flags, SCEV::FlagNUW);
+  }
+
   return Flags;
 }
 


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