From 668c2aa51740da56f26a7488348362916fc77b2c Mon Sep 17 00:00:00 2001
From: Erik Verbruggen <erikjv@me.com>
Date: Thu, 27 Mar 2014 11:16:05 +0000
Subject: [PATCH] InstCombine: merge constants in both operands of icmp.

Transform:
    icmp X+Cst2, Cst
into:
    icmp X, Cst-Cst2
when Cst-Cst2 does not overflow, and the add has nsw.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204912 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Target/README.txt                         | 12 -----
 .../InstCombine/InstCombineCompares.cpp       | 13 +++++
 test/Transforms/InstCombine/icmp.ll           | 53 +++++++++++++++++++
 3 files changed, 66 insertions(+), 12 deletions(-)

diff --git a/lib/Target/README.txt b/lib/Target/README.txt
index a9aab86abda..4ecacf9d010 100644
--- a/lib/Target/README.txt
+++ b/lib/Target/README.txt
@@ -930,18 +930,6 @@ optimized with "clang -emit-llvm-bc | opt -std-compile-opts".
 
 //===---------------------------------------------------------------------===//
 
-int g(int x) { return (x - 10) < 0; }
-Should combine to "x <= 9" (the sub has nsw).  Currently not
-optimized with "clang -emit-llvm-bc | opt -std-compile-opts".
-
-//===---------------------------------------------------------------------===//
-
-int g(int x) { return (x + 10) < 0; }
-Should combine to "x < -10" (the add has nsw).  Currently not
-optimized with "clang -emit-llvm-bc | opt -std-compile-opts".
-
-//===---------------------------------------------------------------------===//
-
 int f(int i, int j) { return i < j + 1; }
 int g(int i, int j) { return j > i - 1; }
 Should combine to "i <= j" (the add/sub has nsw).  Currently not
diff --git a/lib/Transforms/InstCombine/InstCombineCompares.cpp b/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 8c0ad525980..9bf38189542 100644
--- a/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -3008,6 +3008,19 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
     // icmp X, X+Cst
     if (match(Op1, m_Add(m_Value(X), m_ConstantInt(Cst))) && Op0 == X)
       return FoldICmpAddOpCst(I, X, Cst, I.getSwappedPredicate());
+
+    ConstantInt *Cst2;
+    if (match(Op1, m_ConstantInt(Cst)) &&
+        match(Op0, m_Add(m_Value(X), m_ConstantInt(Cst2))) &&
+        cast<BinaryOperator>(Op0)->hasNoSignedWrap()) {
+      // icmp X+Cst2, Cst --> icmp X, Cst-Cst2
+      // iff Cst-Cst2 does not overflow
+      bool Overflow;
+      APInt NewCst = Cst->getValue().ssub_ov(Cst2->getValue(), Overflow);
+      if (!Overflow)
+        return new ICmpInst(I.getPredicate(), X,
+                            ConstantInt::get(Cst->getType(), NewCst));
+    }
   }
   return Changed ? &I : 0;
 }
diff --git a/test/Transforms/InstCombine/icmp.ll b/test/Transforms/InstCombine/icmp.ll
index 12a4744cc0f..2e3ff24f6ba 100644
--- a/test/Transforms/InstCombine/icmp.ll
+++ b/test/Transforms/InstCombine/icmp.ll
@@ -1356,3 +1356,56 @@ define i1 @icmp_ashr_ashr_ne(i32 %a, i32 %b) nounwind {
  %z = icmp ne i32 %x, %y
  ret i1 %z
 }
+
+; CHECK-LABEL: icmp_add_const_const1
+; CHECK: %cmp = icmp slt i32 %x, -10
+; CHECK-NOT: %add = add nsw i32 %x, 10
+define i32 @icmp_add_const_const1(i32 %x) nounwind ssp uwtable {
+entry:
+  %add = add nsw i32 %x, 10
+  %cmp = icmp slt i32 %add, 0
+  %conv = zext i1 %cmp to i32
+  ret i32 %conv
+}
+
+; CHECK-LABEL: icmp_add_const_const2
+; CHECK: %cmp = icmp slt i32 %x, -10
+; CHECK-NOT: %add = add nsw i32 %x, 10
+define i32 @icmp_add_const_const2(i32 %x) nounwind ssp uwtable {
+entry:
+  %add = add nsw i32 10, %x
+  %cmp = icmp sgt i32 0, %add
+  %conv = zext i1 %cmp to i32
+  ret i32 %conv
+}
+
+; CHECK-LABEL: icmp_add_const_const3
+; CHECK: %cmp = icmp slt i32 %x, 20
+; CHECK-NOT: %sub = add nsw i32 %x, -10
+define i32 @icmp_add_const_const3(i32 %x) nounwind ssp uwtable {
+entry:
+  %add = add nsw i32 -10, %x
+  %cmp = icmp sgt i32 10, %add
+  %conv = zext i1 %cmp to i32
+  ret i32 %conv
+}
+
+; CHECK-LABEL: icmp_add_const_intmin
+; CHECK: %cmp = icmp ne i32 %x, 2147483638
+define i32 @icmp_add_const_intmin(i32 %x) nounwind ssp uwtable {
+entry:
+  %add = add nsw i32 %x, 10
+  %cmp = icmp sgt i32 %add, -2147483648
+  %conv = zext i1 %cmp to i32
+  ret i32 %conv
+}
+
+; CHECK-LABEL: icmp_add_const_intmax
+; CHECK: %cmp = icmp ne i32 %x, 2147483637
+define i32 @icmp_add_const_intmax(i32 %x) nounwind ssp uwtable {
+entry:
+  %add = add nsw i32 %x, 10
+  %cmp = icmp slt i32 %add, 2147483647
+  %conv = zext i1 %cmp to i32
+  ret i32 %conv
+}
-- 
2.34.1