From 5d066ff7f0845abd224a4b60cd9bf9f7516b04a6 Mon Sep 17 00:00:00 2001
From: Dan Gohman <gohman@apple.com>
Date: Mon, 17 Sep 2007 17:31:57 +0000
Subject: [PATCH] Instcombine x-((x/y)*y) into a remainder operator.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@42035 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Scalar/InstructionCombining.cpp | 13 ++++++++++++-
 test/Transforms/InstCombine/srem.ll            |  8 ++++++++
 test/Transforms/InstCombine/urem.ll            |  8 ++++++++
 3 files changed, 28 insertions(+), 1 deletion(-)
 create mode 100644 test/Transforms/InstCombine/srem.ll
 create mode 100644 test/Transforms/InstCombine/urem.ll

diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index 787a3d5ccf5..55ef0a80985 100644
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -2257,6 +2257,17 @@ Instruction *InstCombiner::visitSub(BinaryOperator &I) {
         Constant *CP1 = Subtract(ConstantInt::get(I.getType(), 1), C2);
         return BinaryOperator::createMul(Op0, CP1);
       }
+
+      // X - ((X / Y) * Y) --> X % Y
+      if (Op1I->getOpcode() == Instruction::Mul)
+        if (Instruction *I = dyn_cast<Instruction>(Op1I->getOperand(0)))
+          if (Op0 == I->getOperand(0) &&
+              Op1I->getOperand(1) == I->getOperand(1)) {
+            if (I->getOpcode() == Instruction::SDiv)
+              return BinaryOperator::createSRem(Op0, Op1I->getOperand(1));
+            if (I->getOpcode() == Instruction::UDiv)
+              return BinaryOperator::createURem(Op0, Op1I->getOperand(1));
+          }
     }
   }
 
@@ -2902,7 +2913,7 @@ static unsigned getICmpCode(const ICmpInst *ICI) {
 
 /// getICmpValue - This is the complement of getICmpCode, which turns an
 /// opcode and two operands into either a constant true or false, or a brand 
-/// new /// ICmp instruction. The sign is passed in to determine which kind
+/// new ICmp instruction. The sign is passed in to determine which kind
 /// of predicate to use in new icmp instructions.
 static Value *getICmpValue(bool sign, unsigned code, Value *LHS, Value *RHS) {
   switch (code) {
diff --git a/test/Transforms/InstCombine/srem.ll b/test/Transforms/InstCombine/srem.ll
new file mode 100644
index 00000000000..864775ae08a
--- /dev/null
+++ b/test/Transforms/InstCombine/srem.ll
@@ -0,0 +1,8 @@
+; RUN: llvm-as < %s | opt -instcombine | llvm-dis | grep srem
+
+define i64 @foo(i64 %x1, i64 %y2) {
+	%r = sdiv i64 %x1, %y2
+	%r7 = mul i64 %r, %y2
+	%r8 = sub i64 %x1, %r7
+	ret i64 %r8
+}
diff --git a/test/Transforms/InstCombine/urem.ll b/test/Transforms/InstCombine/urem.ll
new file mode 100644
index 00000000000..24e7463cbaf
--- /dev/null
+++ b/test/Transforms/InstCombine/urem.ll
@@ -0,0 +1,8 @@
+; RUN: llvm-as < %s | opt -instcombine | llvm-dis | grep urem
+
+define i64 @rem_unsigned(i64 %x1, i64 %y2) {
+	%r = udiv i64 %x1, %y2
+	%r7 = mul i64 %r, %y2
+	%r8 = sub i64 %x1, %r7
+	ret i64 %r8
+}