From 1bb93a912199bda15214d1ee7f3c731b8e9b648d Mon Sep 17 00:00:00 2001
From: "Arnaud A. de Grandmaison" <arnaud.adegm@gmail.com>
Date: Mon, 25 Mar 2013 11:47:38 +0000
Subject: [PATCH] Address issues found by Duncan during post-commit review of
 r177856.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@177863 91177308-0d34-0410-b5e6-96231b3b80d8
---
 .../InstCombine/InstCombineCompares.cpp       | 51 +++++++------------
 test/Transforms/InstCombine/icmp.ll           |  4 +-
 2 files changed, 21 insertions(+), 34 deletions(-)

diff --git a/lib/Transforms/InstCombine/InstCombineCompares.cpp b/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 24af2bfaf52..a96e754f3dd 100644
--- a/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -139,38 +139,27 @@ static bool isSignBitCheck(ICmpInst::Predicate pred, ConstantInt *RHS,
   }
 }
 
-/// Returns true if the exploded icmp can be expressed as a comparison to zero
-/// and update the predicate accordingly. The signedness of the comparison is
+/// Returns true if the exploded icmp can be expressed as a signed comparison
+/// to zero and updates the predicate accordingly.
+/// The signedness of the comparison is preserved.
 static bool isSignTest(ICmpInst::Predicate &pred, const ConstantInt *RHS) {
   if (!ICmpInst::isSigned(pred))
     return false;
 
   if (RHS->isZero())
-    return true;
+    return ICmpInst::isRelational(pred);
 
-  if (RHS->isOne())
-    switch (pred) {
-    case ICmpInst::ICMP_SGE:
-      pred = ICmpInst::ICMP_SGT;
-      return true;
-    case ICmpInst::ICMP_SLT:
+  if (RHS->isOne()) {
+    if (pred == ICmpInst::ICMP_SLT) {
       pred = ICmpInst::ICMP_SLE;
       return true;
-    default:
-      return false;
     }
-
-  if (RHS->isAllOnesValue())
-    switch (pred) {
-    case ICmpInst::ICMP_SLE:
-      pred = ICmpInst::ICMP_SLT;
-      return true;
-    case ICmpInst::ICMP_SGT:
+  } else if (RHS->isAllOnesValue()) {
+    if (pred == ICmpInst::ICMP_SGT) {
       pred = ICmpInst::ICMP_SGE;
       return true;
-    default:
-      return false;
     }
+  }
 
   return false;
 }
@@ -1322,17 +1311,15 @@ Instruction *InstCombiner::visitICmpInstWithInstAndIntCst(ICmpInst &ICI,
     ConstantInt *Val = dyn_cast<ConstantInt>(LHSI->getOperand(1));
     if (!Val) break;
 
-    if (!ICI.isEquality()) {
-      // If this is a signed comparison to 0 and the mul is sign preserving,
-      // use the mul LHS operand instead.
-      ICmpInst::Predicate pred = ICI.getPredicate();
-      if (isSignTest(pred, RHS) && !Val->isZero() &&
-          cast<BinaryOperator>(LHSI)->hasNoSignedWrap())
-          return new ICmpInst(Val->isNegative() ?
-                                  ICmpInst::getSwappedPredicate(pred) : pred,
-                              LHSI->getOperand(0),
-                              Constant::getNullValue(RHS->getType()));
-    }
+    // If this is a signed comparison to 0 and the mul is sign preserving,
+    // use the mul LHS operand instead.
+    ICmpInst::Predicate pred = ICI.getPredicate();
+    if (isSignTest(pred, RHS) && !Val->isZero() &&
+        cast<BinaryOperator>(LHSI)->hasNoSignedWrap())
+      return new ICmpInst(Val->isNegative() ?
+                          ICmpInst::getSwappedPredicate(pred) : pred,
+                          LHSI->getOperand(0),
+                          Constant::getNullValue(RHS->getType()));
 
     break;
   }
@@ -1613,7 +1600,7 @@ Instruction *InstCombiner::visitICmpInstWithInstAndIntCst(ICmpInst &ICI,
         }
         break;
       case Instruction::Mul:
-        if (RHSV == 0) {
+        if (RHSV == 0 && BO->hasNoSignedWrap()) {
           if (ConstantInt *BOC = dyn_cast<ConstantInt>(BO->getOperand(1))) {
             // The trivial case (mul X, 0) is handled by InstSimplify
             // General case : (mul X, C) != 0 iff X != 0
diff --git a/test/Transforms/InstCombine/icmp.ll b/test/Transforms/InstCombine/icmp.ll
index 2bfdb5c70bb..446c0e01dca 100644
--- a/test/Transforms/InstCombine/icmp.ll
+++ b/test/Transforms/InstCombine/icmp.ll
@@ -858,7 +858,7 @@ define i1 @icmp_mul(i32 %x) {
 ; CHECK: @icmp_mul_neq0
 ; CHECK-NEXT: icmp ne i32 %x, 0
 define i1 @icmp_mul_neq0(i32 %x) {
-  %mul = mul i32 %x, -12
+  %mul = mul nsw i32 %x, -12
   %cmp = icmp ne i32 %mul, 0
   ret i1 %cmp
 }
@@ -866,7 +866,7 @@ define i1 @icmp_mul_neq0(i32 %x) {
 ; CHECK: @icmp_mul_eq0
 ; CHECK-NEXT: icmp eq i32 %x, 0
 define i1 @icmp_mul_eq0(i32 %x) {
-  %mul = mul i32 %x, 12
+  %mul = mul nsw i32 %x, 12
   %cmp = icmp eq i32 %mul, 0
   ret i1 %cmp
 }
-- 
2.34.1