canonicalize:

-%a + 42
into
42 - %a

previously we were emitting:
-(%a + 42)

This fixes the infinite loop in PR12338. The generated code is still not perfect, though.
Will work on that next

llvm-svn: 158237

2 files changed, 29 insertions, 4 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index c88ceede1f2..00f99741259 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -170,10 +170,11 @@ Instruction *InstCombiner::visitAdd(BinaryOperator &I) {
   // -A + B  -->  B - A
   // -A + -B  -->  -(A + B)
   if (Value *LHSV = dyn_castNegVal(LHS)) {
-    if (Value *RHSV = dyn_castNegVal(RHS)) {
-      Value *NewAdd = Builder->CreateAdd(LHSV, RHSV, "sum");
-      return BinaryOperator::CreateNeg(NewAdd);
-    }
+    if (!isa<Constant>(RHS))
+      if (Value *RHSV = dyn_castNegVal(RHS)) {
+        Value *NewAdd = Builder->CreateAdd(LHSV, RHSV, "sum");
+        return BinaryOperator::CreateNeg(NewAdd);
+      }
     
     return BinaryOperator::CreateSub(RHS, LHSV);
   }
diff --git a/llvm/test/Transforms/InstCombine/pr12338.ll b/llvm/test/Transforms/InstCombine/pr12338.ll
new file mode 100644
index 00000000000..2b5c8f8a74e
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/pr12338.ll
@@ -0,0 +1,24 @@
+; RUN: opt < %s -instcombine -S | FileCheck %s
+
+define void @entry() nounwind {

+entry:

+  br label %for.cond

+

+for.cond:

+  %local = phi <1 x i32> [ <i32 0>, %entry ], [ %phi2, %cond.end47 ]
+; CHECK: sub <1 x i32> <i32 92>, %local

+  %phi3 = sub <1 x i32> zeroinitializer, %local

+  br label %cond.end

+

+cond.false:

+  br label %cond.end

+

+cond.end:

+  %cond = phi <1 x i32> [ %phi3, %for.cond ], [ undef, %cond.false ]

+  br label %cond.end47

+

+cond.end47:

+  %sum = add <1 x i32> %cond, <i32 92>

+  %phi2 = sub <1 x i32> zeroinitializer, %sum

+  br label %for.cond

+}