[PATCH] D89821: [SCEV] Match 'zext (trunc A to iB) to iY' as URem.

[Florian Hahn via Phabricator via llvm-commits]

fhahn created this revision.
fhahn added reviewers: reames, mkazantsev, sanjoy.google.
Herald added subscribers: pengfei, hiraditya.
Herald added a project: LLVM.
fhahn requested review of this revision.

URem operations with constant power-of-2 second operands are modeled as
such. This patch on its own has very little impact (e.g. no changes in
CodeGen for MultiSource/SPEC2000/SPEC2006 on X86 -O3 -flto), but I'll
soon post follow-up patches that make use of it to more accurately
determine the trip multiple.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D89821

Files:
  llvm/lib/Analysis/ScalarEvolution.cpp
  llvm/unittests/Analysis/ScalarEvolutionTest.cpp


Index: llvm/unittests/Analysis/ScalarEvolutionTest.cpp
===================================================================
--- llvm/unittests/Analysis/ScalarEvolutionTest.cpp
+++ llvm/unittests/Analysis/ScalarEvolutionTest.cpp
@@ -63,6 +63,11 @@
                                                    const SCEV *RHS) {
     return SE.computeConstantDifference(LHS, RHS);
   }
+
+  bool matchURem(ScalarEvolution &SE, const SCEV *Expr, const SCEV *&LHS,
+                 const SCEV *&RHS) {
+    return SE.matchURem(Expr, LHS, RHS);
+  }
 };
 
 TEST_F(ScalarEvolutionsTest, SCEVUnknownRAUW) {
@@ -1316,4 +1321,34 @@
   });
 }
 
+TEST_F(ScalarEvolutionsTest, MatchURem) {
+  LLVMContext C;
+  SMDiagnostic Err;
+  std::unique_ptr<Module> M = parseAssemblyString(
+      "target datalayout = \"e-m:e-p:32:32-f64:32:64-f80:32-n8:16:32-S128\" "
+      " "
+      "define void @test(i32 %a, i32 %b) {"
+      "entry: "
+      "  %rem1 = urem i32 %a, 2"
+      "  %rem2 = urem i32 %a, 5"
+      "  %rem3 = urem i32 %a, %b"
+      "  ret void "
+      "} ",
+      Err, C);
+
+  assert(M && "Could not parse module?");
+  assert(!verifyModule(*M) && "Must have been well formed!");
+
+  runWithSE(*M, "test", [&](Function &F, LoopInfo &LI, ScalarEvolution &SE) {
+    for (auto *N : {"rem1", "rem2", "rem3"}) {
+      auto *URemI = getInstructionByName(F, N);
+      auto *S = SE.getSCEV(URemI);
+      const SCEV *LHS, *RHS;
+      EXPECT_TRUE(matchURem(SE, S, LHS, RHS));
+      EXPECT_EQ(LHS, SE.getSCEV(URemI->getOperand(0)));
+      EXPECT_EQ(RHS, SE.getSCEV(URemI->getOperand(1)));
+    }
+  });
+}
+
 }  // end namespace llvm
Index: llvm/lib/Analysis/ScalarEvolution.cpp
===================================================================
--- llvm/lib/Analysis/ScalarEvolution.cpp
+++ llvm/lib/Analysis/ScalarEvolution.cpp
@@ -12750,11 +12750,25 @@
 }
 
 // Match the mathematical pattern A - (A / B) * B, where A and B can be
-// arbitrary expressions.
+// arbitrary expressions. Also match zext (trunc A to iB) to iY, which is used
+// for URem with constant power-of-2 second operands.
 // It's not always easy, as A and B can be folded (imagine A is X / 2, and B is
 // 4, A / B becomes X / 8).
 bool ScalarEvolution::matchURem(const SCEV *Expr, const SCEV *&LHS,
                                 const SCEV *&RHS) {
+  // Try to match 'zext (trunc A to iB) to iY', which is used
+  // for URem with constant power-of-2 second operands. Make sure the size of
+  // the operand A matches the size of the whole expressions.
+  if (const auto *ZExt = dyn_cast<SCEVZeroExtendExpr>(Expr)) {
+    const auto *Trunc = dyn_cast<SCEVTruncateExpr>(ZExt->getOperand(0));
+    if (Trunc && getTypeSizeInBits(Trunc->getOperand()->getType()) ==
+                     getTypeSizeInBits(Expr->getType())) {
+      LHS = Trunc->getOperand();
+      RHS = getConstant(Expr->getType(),
+                        1u << getTypeSizeInBits(Trunc->getType()));
+      return true;
+    }
+  }
   const auto *Add = dyn_cast<SCEVAddExpr>(Expr);
   if (Add == nullptr || Add->getNumOperands() != 2)
     return false;


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