From c65c747bc4ee7d3ca8463d33708bbb2aed38a809 Mon Sep 17 00:00:00 2001
From: Duncan Sands <baldrick@free.fr>
Date: Fri, 28 Oct 2011 18:17:44 +0000
Subject: [PATCH] Fold icmp ugt (udiv X, Y), X to false.  Spotted by my
 super-optimizer in 186.crafty.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@143209 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Analysis/InstructionSimplify.cpp    | 12 ++++++++++++
 test/Transforms/InstSimplify/compare.ll | 24 ++++++++++++++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/lib/Analysis/InstructionSimplify.cpp b/lib/Analysis/InstructionSimplify.cpp
index 31cbbba5962..6bef0aedeec 100644
--- a/lib/Analysis/InstructionSimplify.cpp
+++ b/lib/Analysis/InstructionSimplify.cpp
@@ -1574,6 +1574,9 @@ static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
       // 'srem x, CI2' produces (-|CI2|, |CI2|).
       Upper = CI2->getValue().abs();
       Lower = (-Upper) + 1;
+    } else if (match(LHS, m_UDiv(m_ConstantInt(CI2), m_Value()))) {
+      // 'udiv CI2, x' produces [0, CI2].
+      Upper = CI2->getValue();
     } else if (match(LHS, m_UDiv(m_Value(), m_ConstantInt(CI2)))) {
       // 'udiv x, CI2' produces [0, UINT_MAX / CI2].
       APInt NegOne = APInt::getAllOnesValue(Width);
@@ -1880,6 +1883,15 @@ static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
     }
   }
 
+  // x udiv y <=u x.
+  if (LBO && match(LBO, m_UDiv(m_Specific(RHS), m_Value()))) {
+    // icmp pred (X /u Y), X
+    if (Pred == ICmpInst::ICMP_UGT)
+      return getFalse(ITy);
+    if (Pred == ICmpInst::ICMP_ULE)
+      return getTrue(ITy);
+  }
+
   if (MaxRecurse && LBO && RBO && LBO->getOpcode() == RBO->getOpcode() &&
       LBO->getOperand(1) == RBO->getOperand(1)) {
     switch (LBO->getOpcode()) {
diff --git a/test/Transforms/InstSimplify/compare.ll b/test/Transforms/InstSimplify/compare.ll
index 3ece1189025..57727c9ab76 100644
--- a/test/Transforms/InstSimplify/compare.ll
+++ b/test/Transforms/InstSimplify/compare.ll
@@ -300,6 +300,30 @@ define i1 @udiv2(i32 %X, i32 %Y, i32 %Z) {
 ; CHECK: ret i1 true
 }
 
+define i1 @udiv3(i32 %X, i32 %Y) {
+; CHECK: @udiv3
+  %A = udiv i32 %X, %Y
+  %C = icmp ugt i32 %A, %X
+  ret i1 %C
+; CHECK: ret i1 false
+}
+
+define i1 @udiv4(i32 %X, i32 %Y) {
+; CHECK: @udiv4
+  %A = udiv i32 %X, %Y
+  %C = icmp ule i32 %A, %X
+  ret i1 %C
+; CHECK: ret i1 true
+}
+
+define i1 @udiv5(i32 %X) {
+; CHECK: @udiv5
+  %A = udiv i32 123, %X
+  %C = icmp ugt i32 %A, 124
+  ret i1 %C
+; CHECK: ret i1 false
+}
+
 define i1 @sdiv1(i32 %X) {
 ; CHECK: @sdiv1
   %A = sdiv i32 %X, 1000000
-- 
2.34.1