Add back commit r210029.

The code was actually correct. Sorry for the confusion. I have expanded the
comment saying why the analysis is valid to avoid me misunderstaning it
again in the future.

llvm-svn: 210052

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index c37a9cf..15803f2 100644 (file)
--- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -898,10 +898,20 @@ bool InstCombiner::WillNotOverflowSignedAdd(Value *LHS, Value *RHS) {
   // There are different heuristics we can use for this.  Here are some simple
   // ones.
 
-  // Add has the property that adding any two 2's complement numbers can only
-  // have one carry bit which can change a sign.  As such, if LHS and RHS each
-  // have at least two sign bits, we know that the addition of the two values
-  // will sign extend fine.
+  // If LHS and RHS each have at least two sign bits, the addition will look
+  // like
+  //
+  // XX..... +
+  // YY.....
+  //
+  // If the carry into the most significant position is 0, X and Y can't both
+  // be 1 and therefore the carry out of the addition is also 0.
+  //
+  // If the carry into the most significant position is 1, X and Y can't both
+  // be 0 and therefore the carry out of the addition is also 1.
+  //
+  // Since the carry into the most significant position is always equal to
+  // the carry out of the addition, there is no signed overflow.
   if (ComputeNumSignBits(LHS) > 1 && ComputeNumSignBits(RHS) > 1)
     return true;
 
@@ -1191,6 +1201,11 @@ Instruction *InstCombiner::visitAdd(BinaryOperator &I) {
       return BinaryOperator::CreateOr(A, B);
   }
 
+  if (!I.hasNoSignedWrap() && WillNotOverflowSignedAdd(LHS, RHS)) {
+    Changed = true;
+    I.setHasNoSignedWrap(true);
+  }
+
   return Changed ? &I : nullptr;
 }
 

diff --git a/llvm/test/Transforms/InstCombine/cast.ll b/llvm/test/Transforms/InstCombine/cast.ll
index 4fab92f..0cbfbb0 100644 (file)
--- a/llvm/test/Transforms/InstCombine/cast.ll
+++ b/llvm/test/Transforms/InstCombine/cast.ll
@@ -370,7 +370,7 @@ define zeroext i64 @test43(i8 zeroext %on_off) nounwind readonly {
        ret i64 %C  ;; Should be (add (zext i8 -> i64), -1)
 ; CHECK-LABEL: @test43(
 ; CHECK-NEXT: %A = zext i8 %on_off to i64
-; CHECK-NEXT: %B = add i64 %A, -1
+; CHECK-NEXT: %B = add nsw i64 %A, -1
 ; CHECK-NEXT: ret i64 %B
 }
 

diff --git a/llvm/test/Transforms/InstCombine/ffs-1.ll b/llvm/test/Transforms/InstCombine/ffs-1.ll
index 1dec11d..261f488 100644 (file)
--- a/llvm/test/Transforms/InstCombine/ffs-1.ll
+++ b/llvm/test/Transforms/InstCombine/ffs-1.ll
@@ -103,7 +103,7 @@ define i32 @test_simplify13(i32 %x) {
 ; CHECK-LABEL: @test_simplify13(
   %ret = call i32 @ffs(i32 %x)
 ; CHECK-NEXT: [[CTTZ:%[a-z0-9]+]] = call i32 @llvm.cttz.i32(i32 %x, i1 false)
-; CHECK-NEXT: [[INC:%[a-z0-9]+]] = add i32 [[CTTZ]], 1
+; CHECK-NEXT: [[INC:%[a-z0-9]+]] = add nsw i32 [[CTTZ]], 1
 ; CHECK-NEXT: [[CMP:%[a-z0-9]+]] = icmp ne i32 %x, 0
 ; CHECK-NEXT: [[RET:%[a-z0-9]+]] = select i1 [[CMP]], i32 [[INC]], i32 0
   ret i32 %ret
@@ -114,7 +114,7 @@ define i32 @test_simplify14(i32 %x) {
 ; CHECK-LINUX-LABEL: @test_simplify14(
   %ret = call i32 @ffsl(i32 %x)
 ; CHECK-LINUX-NEXT: [[CTTZ:%[a-z0-9]+]] = call i32 @llvm.cttz.i32(i32 %x, i1 false)
-; CHECK-LINUX-NEXT: [[INC:%[a-z0-9]+]] = add i32 [[CTTZ]], 1
+; CHECK-LINUX-NEXT: [[INC:%[a-z0-9]+]] = add nsw i32 [[CTTZ]], 1
 ; CHECK-LINUX-NEXT: [[CMP:%[a-z0-9]+]] = icmp ne i32 %x, 0
 ; CHECK-LINUX-NEXT: [[RET:%[a-z0-9]+]] = select i1 [[CMP]], i32 [[INC]], i32 0
   ret i32 %ret
@@ -125,7 +125,7 @@ define i32 @test_simplify15(i64 %x) {
 ; CHECK-LINUX-LABEL: @test_simplify15(
   %ret = call i32 @ffsll(i64 %x)
 ; CHECK-LINUX-NEXT: [[CTTZ:%[a-z0-9]+]] = call i64 @llvm.cttz.i64(i64 %x, i1 false)
-; CHECK-LINUX-NEXT: [[INC:%[a-z0-9]+]] = add i64 [[CTTZ]], 1
+; CHECK-LINUX-NEXT: [[INC:%[a-z0-9]+]] = add nsw i64 [[CTTZ]], 1
 ; CHECK-LINUX-NEXT: [[TRUNC:%[a-z0-9]+]] = trunc i64 [[INC]] to i32
 ; CHECK-LINUX-NEXT: [[CMP:%[a-z0-9]+]] = icmp ne i64 %x, 0
 ; CHECK-LINUX-NEXT: [[RET:%[a-z0-9]+]] = select i1 [[CMP]], i32 [[TRUNC]], i32 0

diff --git a/llvm/test/Transforms/InstCombine/rem.ll b/llvm/test/Transforms/InstCombine/rem.ll
index 9f07702..0595a67 100644 (file)
--- a/llvm/test/Transforms/InstCombine/rem.ll
+++ b/llvm/test/Transforms/InstCombine/rem.ll
@@ -127,7 +127,7 @@ define i64 @test14(i64 %x, i32 %y) {
 ; CHECK-LABEL: @test14(
 ; CHECK-NEXT: [[SHL:%.*]] = shl i32 1, %y
 ; CHECK-NEXT: [[ZEXT:%.*]] = zext i32 [[SHL]] to i64
-; CHECK-NEXT: [[ADD:%.*]] = add i64 [[ZEXT]], -1
+; CHECK-NEXT: [[ADD:%.*]] = add nsw i64 [[ZEXT]], -1
 ; CHECK-NEXT: [[AND:%.*]] = and i64 [[ADD]], %x
 ; CHECK-NEXT: ret i64 [[AND]]
        %shl = shl i32 1, %y

diff --git a/llvm/test/Transforms/InstCombine/select.ll b/llvm/test/Transforms/InstCombine/select.ll
index 23a891a..762a9da 100644 (file)
--- a/llvm/test/Transforms/InstCombine/select.ll
+++ b/llvm/test/Transforms/InstCombine/select.ll
@@ -281,7 +281,7 @@ define i32 @test15i(i32 %X) {
 ; CHECK-NEXT: %t1 = shl i32 %X, 8
 ; CHECK-NEXT: %1 = and i32 %t1, 512
 ; CHECK-NEXT: %2 = xor i32 %1, 512
-; CHECK-NEXT: %3 = add i32 %2, 577
+; CHECK-NEXT: %3 = add nsw i32 %2, 577
 ; CHECK-NEXT: ret i32 %3
 }
 
@@ -294,7 +294,7 @@ define i32 @test15j(i32 %X) {
 ; CHECK-LABEL: @test15j(
 ; CHECK-NEXT: %t1 = shl i32 %X, 8
 ; CHECK-NEXT: %1 = and i32 %t1, 512
-; CHECK-NEXT: %2 = add i32 %1, 577
+; CHECK-NEXT: %2 = add nsw i32 %1, 577
 ; CHECK-NEXT: ret i32 %2
 }
 
@@ -521,7 +521,7 @@ define i32 @test35(i32 %x) {
 ; CHECK-LABEL: @test35(
 ; CHECK: ashr i32 %x, 31
 ; CHECK: and i32 {{.*}}, 40
-; CHECK: add i32 {{.*}}, 60
+; CHECK: add nsw i32 {{.*}}, 60
 ; CHECK: ret
 }
 
@@ -532,7 +532,7 @@ define i32 @test36(i32 %x) {
 ; CHECK-LABEL: @test36(
 ; CHECK: ashr i32 %x, 31
 ; CHECK: and i32 {{.*}}, -40
-; CHECK: add i32 {{.*}}, 100
+; CHECK: add nsw i32 {{.*}}, 100
 ; CHECK: ret
 }
 

diff --git a/llvm/test/Transforms/InstCombine/sext.ll b/llvm/test/Transforms/InstCombine/sext.ll
index b8dfe22..f04afcc 100644 (file)
--- a/llvm/test/Transforms/InstCombine/sext.ll
+++ b/llvm/test/Transforms/InstCombine/sext.ll
@@ -145,7 +145,7 @@ define i32 @test13(i32 %x) nounwind {
 ; CHECK-LABEL: @test13(
 ; CHECK-NEXT: %and = lshr i32 %x, 3
 ; CHECK-NEXT: %1 = and i32 %and, 1
-; CHECK-NEXT: %sext = add i32 %1, -1
+; CHECK-NEXT: %sext = add nsw i32 %1, -1
 ; CHECK-NEXT: ret i32 %sext
 }
 
@@ -157,7 +157,7 @@ define i32 @test14(i16 %x) nounwind {
 ; CHECK-LABEL: @test14(
 ; CHECK-NEXT: %and = lshr i16 %x, 4
 ; CHECK-NEXT: %1 = and i16 %and, 1
-; CHECK-NEXT: %sext = add i16 %1, -1
+; CHECK-NEXT: %sext = add nsw i16 %1, -1
 ; CHECK-NEXT: %ext = sext i16 %sext to i32
 ; CHECK-NEXT: ret i32 %ext
 }

diff --git a/llvm/test/Transforms/InstCombine/zext-bool-add-sub.ll b/llvm/test/Transforms/InstCombine/zext-bool-add-sub.ll
index d7f338b..6fa4d70 100644 (file)
--- a/llvm/test/Transforms/InstCombine/zext-bool-add-sub.ll
+++ b/llvm/test/Transforms/InstCombine/zext-bool-add-sub.ll
@@ -6,7 +6,7 @@ entry:
 ; CHECK-LABEL: @a(
 ; CHECK: [[TMP1:%.*]] = sext i1 %y to i32
 ; CHECK: [[TMP2:%.*]] = select i1 %x, i32 2, i32 1
-; CHECK-NEXT: add i32 [[TMP2]], [[TMP1]]
+; CHECK-NEXT: add nsw i32 [[TMP2]], [[TMP1]]
   %conv = zext i1 %x to i32
   %conv3 = zext i1 %y to i32
   %conv3.neg = sub i32 0, %conv3