Add an instcombine for constructs like a | -(b != c); a select is more

canonical, and generally leads to better code.  Found while looking at
an article about saturating arithmetic.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@129545 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 27 insertions, 1 deletions

diff --git a/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index 1cb18e12ee..6cf405328a 100644
--- a/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -2003,7 +2003,14 @@ Instruction *InstCombiner::visitOr(BinaryOperator &I) {
       }
     }
   }
-  
+
+  // or(sext(A), B) -> A ? -1 : B where A is an i1
+  // or(A, sext(B)) -> B ? -1 : A where B is an i1
+  if (match(Op0, m_SExt(m_Value(A))) && A->getType()->isIntegerTy(1))
+    return SelectInst::Create(A, ConstantInt::getSigned(I.getType(), -1), Op1);
+  if (match(Op1, m_SExt(m_Value(A))) && A->getType()->isIntegerTy(1))
+    return SelectInst::Create(A, ConstantInt::getSigned(I.getType(), -1), Op0);
+
   // Note: If we've gotten to the point of visiting the outer OR, then the
   // inner one couldn't be simplified.  If it was a constant, then it won't
   // be simplified by a later pass either, so we try swapping the inner/outer
diff --git a/test/Transforms/InstCombine/or.ll b/test/Transforms/InstCombine/or.ll
index f82f9faab2..94a5732186 100644
--- a/test/Transforms/InstCombine/or.ll
+++ b/test/Transforms/InstCombine/or.ll
@@ -390,3 +390,22 @@ define i1 @test36(i32 %x) {
 ; CHECK-NEXT: ret i1
 }
 
+define i32 @test37(i32* %xp, i32 %y) {
+; CHECK: @test37
+; CHECK: select i1 %tobool, i32 -1, i32 %x
+  %tobool = icmp ne i32 %y, 0
+  %sext = sext i1 %tobool to i32
+  %x = load i32* %xp
+  %or = or i32 %sext, %x
+  ret i32 %or
+}
+
+define i32 @test38(i32* %xp, i32 %y) {
+; CHECK: @test38
+; CHECK: select i1 %tobool, i32 -1, i32 %x
+  %tobool = icmp ne i32 %y, 0
+  %sext = sext i1 %tobool to i32
+  %x = load i32* %xp
+  %or = or i32 %x, %sext
+  ret i32 %or
+}