From 786792784e898f29febb3e7270d54b0e21e3c904 Mon Sep 17 00:00:00 2001
From: Nick Lewycky <nicholas@mxc.ca>
Date: Fri, 4 Mar 2011 10:06:52 +0000
Subject: [PATCH] Fold "icmp pred (srem X, Y), Y" like we do for urem. Handle
 signed comparisons in the urem case, though not the other way around. This is
 enough to get #3 from PR9343!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@126991 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Analysis/InstructionSimplify.cpp    | 31 ++++++++++++++++++++++++-
 test/Transforms/InstCombine/icmp.ll     | 13 +++++++++--
 test/Transforms/InstSimplify/compare.ll | 18 ++++++++++++++
 3 files changed, 59 insertions(+), 3 deletions(-)

diff --git a/lib/Analysis/InstructionSimplify.cpp b/lib/Analysis/InstructionSimplify.cpp
index 3cfb2b7637e..44b0247e5ae 100644
--- a/lib/Analysis/InstructionSimplify.cpp
+++ b/lib/Analysis/InstructionSimplify.cpp
@@ -1671,14 +1671,28 @@ static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
     }
   }
 
-  if (LBO && match(LBO, m_URem(m_Value(), m_Specific(RHS)))) {
+  Value *V;
+  if (LBO && match(LBO, m_URem(m_Value(V), m_Specific(RHS)))) {
+    bool KnownNonNegative, KnownNegative;
     switch (Pred) {
     default:
       break;
+    case ICmpInst::ICMP_SGT:
+    case ICmpInst::ICMP_SGE:
+      ComputeSignBit(LHS, KnownNonNegative, KnownNegative, TD);
+      if (!KnownNonNegative)
+        break;
+      // fall-through
     case ICmpInst::ICMP_EQ:
     case ICmpInst::ICMP_UGT:
     case ICmpInst::ICMP_UGE:
       return ConstantInt::getFalse(RHS->getContext());
+    case ICmpInst::ICMP_SLT:
+    case ICmpInst::ICMP_SLE:
+      ComputeSignBit(LHS, KnownNonNegative, KnownNegative, TD);
+      if (!KnownNonNegative)
+        break;
+      // fall-through
     case ICmpInst::ICMP_NE:
     case ICmpInst::ICMP_ULT:
     case ICmpInst::ICMP_ULE:
@@ -1686,6 +1700,21 @@ static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
     }
   }
 
+  if (LBO && match(LBO, m_SRem(m_Value(), m_Specific(RHS)))) {
+    switch (Pred) {
+    default:
+      break;
+    case ICmpInst::ICMP_EQ:
+    case ICmpInst::ICMP_SGT:
+    case ICmpInst::ICMP_SGE:
+      return ConstantInt::getFalse(RHS->getContext());
+    case ICmpInst::ICMP_NE:
+    case ICmpInst::ICMP_SLT:
+    case ICmpInst::ICMP_SLE:
+      return ConstantInt::getTrue(RHS->getContext());
+    }
+  }
+
   // If the comparison is with the result of a select instruction, check whether
   // comparing with either branch of the select always yields the same value.
   if (isa<SelectInst>(LHS) || isa<SelectInst>(RHS))
diff --git a/test/Transforms/InstCombine/icmp.ll b/test/Transforms/InstCombine/icmp.ll
index ff11bbff77c..fba273550b1 100644
--- a/test/Transforms/InstCombine/icmp.ll
+++ b/test/Transforms/InstCombine/icmp.ll
@@ -379,7 +379,7 @@ define i1 @test38(i32 %x, i32 %y, i32 %z) {
 }
 
 ; PR9343 #1
-; CHECK: test39
+; CHECK: @test39
 ; CHECK %B = icmp eq i32 %X, 0
 define i1 @test39(i32 %X, i32 %Y) {
   %A = ashr exact i32 %X, %Y
@@ -387,10 +387,19 @@ define i1 @test39(i32 %X, i32 %Y) {
   ret i1 %B
 }
 
-; CHECK: test40
+; CHECK: @test40
 ; CHECK: %B = icmp ne i32 %X, 0
 define i1 @test40(i32 %X, i32 %Y) {
   %A = lshr exact i32 %X, %Y
   %B = icmp ne i32 %A, 0
   ret i1 %B
 }
+
+; PR9343 #3
+; CHECK: @test41
+; CHECK: ret i1 true
+define i1 @test41(i32 %X, i32 %Y) {
+  %A = urem i32 %X, %Y
+  %B = icmp ugt i32 %Y, %A
+  ret i1 %B
+}
diff --git a/test/Transforms/InstSimplify/compare.ll b/test/Transforms/InstSimplify/compare.ll
index 44c678c6f11..11295b7072b 100644
--- a/test/Transforms/InstSimplify/compare.ll
+++ b/test/Transforms/InstSimplify/compare.ll
@@ -236,6 +236,15 @@ define i1 @urem4(i32 %X) {
 ; CHECK: ret i1 %B
 }
 
+define i1 @urem5(i16 %X, i32 %Y) {
+; CHECK: @urem5
+  %A = zext i16 %X to i32
+  %B = urem i32 %A, %Y
+  %C = icmp slt i32 %B, %Y
+  ret i1 %C
+; CHECK: ret i1 true
+}
+
 define i1 @srem1(i32 %X) {
 ; CHECK: @srem1
   %A = srem i32 %X, -5
@@ -244,6 +253,15 @@ define i1 @srem1(i32 %X) {
 ; CHECK: ret i1 false
 }
 
+define i1 @srem2(i32 %X, i32 %Y) {
+; CHECK: @srem2
+  %neg = sub i32 %Y, 0
+  %A = srem i32 %X, %Y
+  %B = icmp slt i32 %A, %neg
+  ret i1 %B
+; CHECK: ret i1 true
+}
+
 define i1 @udiv1(i32 %X) {
 ; CHECK: @udiv1
   %A = udiv i32 %X, 1000000