Added instcombine pattern to spot comparing -val or val against 0.

(val != 0) == (-val != 0) so "abs(val) != 0" becomes "val != 0"

Fixes <rdar://problem/10482509>

llvm-svn: 145563

2 files changed, 24 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 274758ccb4b..cebe37b7b0a 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -1795,6 +1795,20 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
   if (Value *V = SimplifyICmpInst(I.getPredicate(), Op0, Op1, TD))
     return ReplaceInstUsesWith(I, V);
 
+  // comparing -val or val with non-zero is the same as just comparing val
+  // ie, (val != 0) == (-val != 0)
+  if (I.getPredicate() == ICmpInst::ICMP_NE && match(Op1, m_Zero()))
+  {
+    Value *Cond, *SubSrc, *SelectFalse;
+    if (match(Op0, m_Select(m_Value(Cond), m_Sub(m_Zero(), m_Value(SubSrc)),
+                            m_Value(SelectFalse)))) {
+      if (SubSrc == SelectFalse) {
+        return CmpInst::Create(Instruction::ICmp, I.getPredicate(),
+                               SubSrc, Op1);
+      }
+    }
+  }
+
   Type *Ty = Op0->getType();
 
   // icmp's with boolean values can always be turned into bitwise operations
diff --git a/llvm/test/Transforms/InstCombine/compare-abs-nonzero.ll b/llvm/test/Transforms/InstCombine/compare-abs-nonzero.ll
new file mode 100644
index 00000000000..49cd688bda0
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/compare-abs-nonzero.ll
@@ -0,0 +1,10 @@
+; RUN: opt < %s -instcombine -S | grep -v {select}
+
+define zeroext i1 @cmpabs(i64 %val) nounwind uwtable readnone ssp {
+entry:
+  %sub = sub nsw i64 0, %val
+  %cmp = icmp slt i64 %val, 0
+  %sub.val = select i1 %cmp, i64 %sub, i64 %val
+  %tobool = icmp ne i64 %sub.val, 0
+  ret i1 %tobool
+}